Download ASTR-100 - Jiri Brezina Teaching

ASTR-100
Introduction to ASTRONOMY
17 Jan – 9 Mar 06
Tu, Th (Sa); 17:00 – 19:45h
LECTURER: Dr. Jiri Brezina,
phone/fax (civilian):
06223-7014/-3421
Heidelberger Str 68, Waldhilsbach
email:
[email protected]
69 151 Neckargemünd
Teaching homepage: http://teaching.grano.de/
GPS: N 49° 22’ 40.3687” = 49.377880205°;
E 8° 46’ 08.5719” = 8.769047770°
TEXTBOOK: Horizons - Exploring the Universe, by Seeds; Brooks/Cole, Pacific Grove, CA 9th edition 2006
Amateur Astronomy, by Colin Ronan (ed.); Hamlyn, 1989, 256 pages;
Stars & Stripes $9.95
OPTIONAL
Go Skywatching, by Ian Ridpath; Hamlyn, 1987, 160 pages;
Stars & Stripes $6.95
READING:
Monthly magazines Astronomy, The Planetary Report, Scientific American, Science,
Science Digest, National Geographic; weekly magazine Science News, etc.
Dance of Planets, a PC program from: ARC-Simulation Software, Loveland, CO 80539-1974 (V. 2.71: $50)
Kaiserslautern ROB, Bld. 285, Rm. 4
INTERNET:
http://www.arcscience.com/dance.htm; Encyclopaedia Britannica: http://www.eb.com
Your eMail Subject must always start with:
Main document:
A0+1_ROB_J-M06_TuTh:█<your subject> █= space; 0 is zero, not the capital O (as in ROB)
D:\P2_300MHz_HOME\P2_DAT E\Docs\Ww\Umd\Astr-100\A0GD06.doc

Printed: Sun, 7 May 17, 10:08h
http://teaching.grano.de/A0GD05.doc
Decimal numbers refer to textbook figures, boxes, etc.
bold numbers to textbook Chapters,
numbers to textbook pages;
TG = this Textbook Guide
TEXTBOOK GUIDE
Class-Meeting
#
Date
1 Error! Reference source not found., Error! Reference source not found. Error! Reference
source not found. 06
ASTRONOMY (Greek: astron = star; -nomos from Greek nemein = to arrange; Greek “astronomos” = star-arranger).
The New Columbia Encyclopedia (4th edition of The Columbia Encyclopedia, Columbia University Press, New York - London, 1975, 3052 pages):
Branch of science that studies the motion and nature of celestial bodies, such as planets, stars, and galaxies; more generally, the study of matter and energy
in the universe at large. A. is perhaps the oldest of the pure sciences. It originated from man’s search for his position in the world using observation, but it
had a lot of practical functions too, such as a basis for the calendar, for navigation and time-keeping, etc.. Modern astronomy’s new and powerful tool,
space research, has resulted in great progress in computers, communication etc..
The Scale of the Cosmos (1, 2-8): optional. http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ http://www.wordwizz.com/pwrsof10.htm
Search in Google for Charles Eames (1907-1978): http://www.powersof10.com/ http://www.powersof10.com/powers/space/station_244
The EARTH & SKY (2 & 3, 9 - 39)
Stars are grouped into 88 constellations (asterisms, 14-16) on the sky; a rectangular area around each
constellation can be used for a rough position of an object in the sky; object’s position can be more
specified by referring to the closest constellation star. A constellation is a pattern of stars as seen from the Earth (Fig. 2-3,
15); these stars are not physically associated, and, due to their motion relative to the solar system, the pattern changes slowly.
In order of decreasing apparent brightness (intensity), or increasing “class-order” defined as apparent
visual magnitude (16-18, Fig. 2-6, 16), Greek letters identify the constellation stars (Fig. 2-4, 15,: the
brightest star is designated  [alpha], the second brightest  [beta], and so on). Norman Pogson (1856)
has adjusted the Hipparchus' “six magnitude classes” to the actually measured brightness (intensity). He
defined these two scales by the following relationship (Reasoning with Numbers 2-1, 17):
magnitude = -lognbrightness = -n x logBRI. This reads “magnitude equals to the negative logarithm (to
the base n) of the brightness” where n is the base of the logarithm and equals to the brightness (intensity)
ratio for a magnitude difference of 1: n = 1000.2 = 1001/5 = 2.511886432. Conversely, brightness =
nmagnitude = 100MAG/5. Therefore, a magnitude difference of 5 corresponds to a brightness ratio of 100; a
magnitude difference of 1 corresponds to a brightness ratio of n = 1000.2 = 100(1/5) = 2.511886432.
To divide the visible stars into six brightness values was no personal idiosyncrasy of Hipparchus. It was due, although he did not realize it, to an in-built
human physical mechanism of perception which operates on any change of stimulus on a logarithmic scale (the Weber - Fechner law).
Magnitude (Tab. 2-1, p. 17: extend it for negative values as on Fig. 2-6; p. 16) is related to brightness as follows:
brightness:
magnitude:
1 000 000
-15
10 000
-10
100
-5
1
0
0.01
+5
0.000 1
+10
0.000 001
+15
Position of an object in the sky (celestial sphere). Coordinates on the Earth are known as latitude
(angular distance north or south of equator [= 0°]) and longitude (angular distance east or west of the
prime meridian through Greenwich; a meridian is a great circle that passes through both poles). On the
celestial sphere, declination (abbreviated as DEC or ) is used instead of latitude, right ascension
(abbreviated as RA or , measured in units of time [hours] eastward from vernal equinox (28 top, TG p.
2) is used instead of longitude, it is. Position of Polaris (the North Star) changes very little (due to the Earth’s precession, 1819) because it lies nearly directly over the North Pole, on the extended axis of the Earth’s rotation. Textbook mistake: vernall
comes from the Latin ver, -is, n. = spring (from the Greek er, eros); vernalis; vernus, -a, -um = spring related (not green: green = viridis in Latin
= verde in Spanish. Equinox comes from the Latin aequinoctium: aequus, -a, -um = equal, nox, noctis f. = night.
The mean distance Earth – Sun, known as astronomical unit, AU, is about 150 million km (Fig. 1-6, 6; exactly
149,597,870 km, Celestial Profile 2, 383); this distance is passed by light within 499.0047815 sec = 8.316746358
min  8 min 19 sec. A greater distance unit is parsec, pc (TG-p. 17): the distance at which a star would have a
parallax of one second of arc (parallax is the half observation angle using a base line of 2 AU, i.e. at six-monthly
interval). A popular distance unit is a light-year, a distance light (and any elmag radiation) travels in one year =
9.51012 km. 1 parsec = 3.26 light years (the light speed in vacuum is c = 299,792.458 meter/sec [PTB,
Braunschweig, November 1983]; the inverse value, 1/c = c-1 = the time during which the light passes 1 meter =
3.335,640,95210-9 sec/meter, defines the standard length of meter). The wavelength  (lambda) of an elmag
radiation is related to its frequency f as follows: f = c [meter/second]. This way, the frequency can be
calculated from the wavelength and vice versa: f = c/, = c/f. More about the elmag radiation (light is one type
of it only): TG-p. 4. The mean distance between the Earth and Moon is = 384,401 km; it also equals 0.002569562
AU, 1 AU = 389.171,386 of the Moon – Earth distance.
1
Part 1: Earth + Sky, Kepler’s+ Newton‘s laws.
Matter + radiation, astronomical tools
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printed: 7-May-17, 10:08h
The MOVING EARTH, MOON & PLANETS (3)
The Earth, our observation site, performs multiple motion which changes the observed portion of the
sky: rotation on its axis (one full period equals a sidereal day with respect to the stars, in contrary to the
current solar day which is the period of the Earth’s rotation with respect to the Sun) and revolution
(orbiting) about the Sun (one full period equals an astronomical year).
The Earth’s rotational velocity on equator is the equator’s length per day = 40,074/24 km/hour = 1669.8 km/hour = 464 meter/second;
the Earth’s rotational velocity at our (50°) latitude = 464cos50° meter/second = 464 0.64279 meter/second = 298 meter/second.
Ecliptic (26, 28) is the plane of the Earth’s orbit (its projection on the sky; it corresponds to the yearly
apparent path of the Sun on the sky). The daily angular motion is 360° divided by 365.2564 days =
approx. 1°/day (twice the Sun’s angular diameter). The average orbital velocity is 29.79 km/sec. The
celestial equator is tipped by 23.45° to the ecliptic (28, top). These two planes cross at places of equal
day and night, equinoxes: vernal equinox is the place where the Sun moves northward (about 21
March), it marks the beginning of spring, and the autumnal equinox is the place where it crosses moving
southward (about 21 Sep.), it marks the beginning of fall. The sun is farthest north at the point called the
summer solstice about 21 June, (the longest day, beginning of summer on the North Hemisphere), the
sun is farthest south at the winter solstice, about 21 Dec. (the shortest day, beginning of winter on the
North Hemisphere). These seasons alternate on the North and South Hemispheres, this is why they are
called hemispheric seasons. The changing distance planet – Sun, due to the planet’s elliptical orbit,
influences the whole planet’s temperature; the resulting seasons are called global seasons (see below).
Looking ‘down’ on the Earth’s North Pole, both its axial rotation and revolution (orbiting) are counterclockwise (ccw). This is termed direct rotation, while the word retrograde is applied to the rotation if
opposite to the revolution. Objects with retrograde rotation have inclination to orbit greater than 90°
(such as Venus, 177.3°; Uranus, 97.86°; and Pluto 112.52°; C. D. MURRAY & S. F. DERMOTT (CUP, 1999), Solar System
Dynamics, Tab. A.4, p. 531). The revolution (orbiting) is ccw when seen from north on all planets and most of
their satellites; the axial rotation is ccw when seen from north only on 6 from 9 planets and on several of
their 131 satellites. Since the stars seem to make 366 revolutions in a year (365 due to the rotation of the
Earth on its axis, and one extra rotation because the Earth has orbited once round the Sun), the sidereal
day is shorter than the solar day (23 hours 56 minutes 4.1 seconds of mean solar time). This is why the
stars appear to rise about 4 minutes (24 hours divided by 365.2564 days) earlier each night - the sky
moves eastward. Sun, most outer planets (exceptions are retrograde loops, Figs. 4-3, 4-4, 4-6; 50-8) and
particularly Moon drift eastward from day to day.
The Earth’s rotational axis is tilted by 23.45° to the perpendicular of ecliptic, the Earth’s orbital plane.
Whereas the tilt is almost constant, the axis direction slowly precedes. The precession period is about
26,000 years (0.014°/year). The Earth’s axis traces out a cone in space (Fig. 2.7, 18-9), due to
gravitational influence of the Sun and Moon on the Earth’s equatorial bulge: it is trying to make the
Earth spin upright (in respect to its orbit).
A solar system body may experience two types of seasons:
1. Alternating hemispheric seasons caused by a tilt of the object’s rotational axis to the perpendicular
of its orbital plane (26-7). This type of seasons is reversed on the north & south hemispheres, dominates
on the Earth, and is effective on Mars. Then: summer is warmer than winter because (28-9):
a) summer sun shines longer than the winter sun;
b) summer sun shines higher, strikes the surface more perpendicularly, its light is more concentrated per
area, casts shorter shadows (Figs. on top of the page 29).
2. Global seasons caused by changing distance from the Sun due to object’s elliptical (eccentric) orbit;
they occur simultaneously overall an object, on both hemispheres. Global seasons dominate on Mars,
Mercury, and Pluto. Because the Earth’s orbit is slightly elliptic (Earth is closest to the Sun around 4
January, farthest around 4 July), this global seasonal effect makes the dominating hemispheric seasons
slightly milder on the Northern Hemisphere, and slightly stronger on the Southern Hemisphere (“Inquire
1 Review 1 Analyze”, 30).
2 Error! Reference source not found., Error! Reference source not found. Jan 06MOTIONS
Moon (30-40, 387-395) is the nearest celestial body: mean distance 384,401 km (light reaches it within
1.28222 sec). Its mean diameter of 3476.2 km (a little more than a quarter of the Earth’s diameter) places it
among the largest satellites in the solar system: it is larger than Pluto [3100 km], Europa [3130 km]
(Jupiter’s satellite), and Triton [2704 km] (Neptune’s satellite). Slightly larger solar bodies than the
Moon are: Io [3640 km] & Callisto [4840 km] (both Jupiter’s satellites), Mercury [4878 km], Titan
[5150 km] (Saturn’s satellite), and the biggest satellite Ganymede [5280 km] (Jupiter’s one). Moon’s
mass is 0.0123 of the Earth’s mass, Moon’s surface gravity is 0.167 of the Earth’s one; Moons mean
density is 3.36 g/cm3.
Seen from the Earth, the Moon’s side is illuminated by Sun in a periodically repeating cycle of phases
(31, Fig. 3.3): new moon, new (waxing) crescent, first quarter, first (waxing) gibbous, full moon, last
(waning) gibbous, last (third) quarter, old (waning) crescent. Whereas the new moon occurs nearby the
Sun, the full moon appears on the opposite side to the Sun.
Part 1: Earth + Sky, Kepler’s+ Newton’s laws.
Matter + radiation, astronomical tools
3
ASTR-100, «EDC»
printed: 7-May-17, 10:08h
The Moon orbits Earth in 27.321661 days (Moon’s sidereal orbital period; 33, 391), the Earth orbits Sun
in 365.2564 days in the same (counter-clockwise, eastward) direction. See: http://www.nationmaster.com/encyclopedia/Sidereal-year
During the Moon’s sidereal period, the sun moves eastward about 1°/day (360°/365.2564 days) = about
27° (26.928474° more exactly) eastward; this is why the moon needs slightly more than two days to
catch up with the sun to reach the same phase. Thus one cycle of lunar phases takes 29.53 days (Moon’s
synodic [phase] period; 33).
The Moon occurs within or outside of the space between the Earth and Sun. Because the Moon’s orbit
around the Earth is slightly tilted (5.15°) to the ecliptic, the Moon does not occur on the Earth-Sun line
on each full and new moon, and the three bodies do not always occult each other (Fig. 3-13, 39). Only
during some new and full moons, the eclipse of Sun and Moon respectively can occur. This happens at
the intersection of the Moon’s orbital plain with the ecliptic when the intersection line (the line of
Moon’s orbital nodes, 39, Fig. 3.14, 40) passes the Sun. This occurs twice a year, during an interval of
about two weeks (called eclipse season, 39), and when the Moon passes the ecliptic (at new and full
moons). In fact, the lunar eclipse is no real eclipse of the Moon, it is only its shadowing. Therefore,
when it occurs, it is visible from almost the whole Earth’s hemisphere where the full moon is visible. An
observer on the Moon would observe the Sun eclipsed by the Earth.
If the Moon’s orbital plane were fixed in space, the eclipse seasons would always occur at the same time each year. However, because of the gravitational
pull of the Sun on the Moon, the Moon’s orbit precedes slowly westwards completing one rotation in 18.61 years. Therefore, the eclipse seasons occur
about three weeks earlier each year. The precessional motion of the line of nodes, combined with the lunar phase periodicity, means that every 18 years, 11
+ 1/3 days (6585.32 days = 223 synodic months = about 19 eclipse years) the eclipse seasons start over: the same pattern of eclipses repeats (Saros cycle).
Tides on the Earth (67, 70-71) are caused by gravity pull of the Moon and the Sun. Tides refer not only
to rising and sinking of waters but of atmosphere and of the “solid” crust. Because the bulging is
changing due to the Earth’s rotation and changing its distance from the Sun and Moon, these motions
cause friction and heating which may explain subsurface magmatism & volcanism (see TG.-p. 7 [Earth], 10-11);
Carl D. MURRAY & Stanley F. DERMOTT, Solar System Dynamics; Cambridge University Press, 1999, 592 pages; ISBN 0-521-57597-4.
Terrestrial planets and many satellites of the solar system are not perfectly rigid. If they are subject to a changing gravity pull
from neighbor bodies in direction and/or strength, they deform, a this deformation constantly changes (flexing). For
example, the gravity fields of the Moon and the Sun draw up the near side rocky surface of the Earth rotating daily on its axis,
into a bulge a few inches high (page 70). The deformation change (driven by orbiting and spinning energies of all involved
bodies) is resisted by internal friction, which causes heating. This way, the rotational (and, if applicable orbiting) energy is
consumed and the driving motions become slower.
The tidal heating can be remotely observed only if a resulting volcanism can be observed, which may form as follows: the tidally generated heat cumulates
in the subsurface material (the overlying material insulates from heat losses) and causes its melting, eventually degassing or partial vaporization. These
results are known on several solid bodies of the Solar system. Planetologists call them volcanism, even if the melting/vaporization takes place at a very low
temperature (such as that on Triton – at –210°C [=63 Kelvin]).
On the Earth, magmatic chambers are located shallow within the crust and are slowly rising due to convection currents of the magma. The hot magma
rises to the chamber’s ceiling; the ceiling rocks melt and cool the magma which sinks to the chamber’s bottom and crystallizes into igneous (magmatic)
rocks. The magma contains a great percentage of (volcanic) gases dissolved under high pressure. As a magmatic chamber rises, the pressure acting on the
magma from overlaying rocks decreases. When this pressure becomes lower than the magmatic gas pressure, the compressed dissolved gases abruptly
separate from the solution, form bubbles: an explosion takes place and forms a volcano.
Tidal heating slows the bodies' rotation until it becomes tidally locked, and the tidal bulge does not change any more.
Two (from many) examples of tidal heating:
Moon’s rotation, originally faster than now (the Moon showed all sides earlier), has been tidally locked to the Earth since 3.5
bill. y. ago (29), thus it does not have any active volcanism since that time .
Io (the closest Galilean moon of Jupiter). The heat driving Io’s strong volcanism (strongest in the solar system) comes from tidal
heating (377-8). Io is subject to constantly changing deformation (flexing) by its rotation in its orbit around Jupiter (in its strong gravity
field), and by closely approaching Ganymede (the largest solar system satellite) and Europa. In fact, these tidal heating causes are three:
1 Io rotates in the Jupiter’s strong gravity field;
2 Io’s neighbor satellites Ganymede and Europa flex Io at every conjunction with Io;
3 Ganymede, the biggest satellite of the solar system, pulls Io’s orbit into elliptical (eccentric) one at each conjunction with Io.
Pluto + its satellite Charon, each is tidally locked to other (Pluto’s day = Charon’s orbit period = Charon’s day = 6 days, 9 hours, and 18 minutes; 394;
Astronomy, July 1986, page 17); therefore, the gravity pull of Charon does not change on Pluto, and there is no tidal heating on Pluto. Of course, Pluto’s
extremely eccentric orbit (the strongest among the solar system planets), may cause some tidal heating on Pluto; however, such an effect has not yet been
observed due to very limited knowledge about Pluto (the only planet not visited by a man-made spacecraft).
3 Error! Reference source not found., Error! Reference source not found. Jan 06QUIZ 1 (30 minutes)
Position of an object on sky - identified by: 1 the object’s location in a constellation (and within it, by a reference to the nearest star); 2 co-ordinates of the
celestial sphere (declination, similar to the Earth’s latitude, and right ascension in hours eastwards from vernal equinox, similar to the Earth’s longitude).
Celestial poles & celestial equator. Ecliptic. Magnitude & brightness. Seasons on the Earth. Solar & lunar eclipses (explanation of their frequency), tides.
Kepler’s laws of orbital motion (4.4)
Johannes KEPLER (57-60; born 27-Dec-1571 in Magstadt [18km SW from Stuttgart, SW Germany, Württemberg; Kepler’s museum is nearby in Weil der
Stadt: http://www.kepler-museum.de/d/links.html, http://www.kepler.arc.nasa.gov/kepler_sites.html], died 15 Nov. 1630 in Regensburg, SE Germany,
Bavaria) studied in Tübingen (S Germany) to become a Lutheran pastor. During his last year of study, Kepler accepted a job in Graz (Austria) teaching
mathematics and astronomy and preparing an annual almanac that contained astronomical, astrological and weather predictions. Good luck in weather
predictions 1595 gave him a reputation as an astrologer and seer. While still a college student, Kepler had become a believer in the Copernican heliocentric
hypothesis and at Graz he used his spare time to study astronomy. Tycho de Brahe invited him to Prague, the capital of Bohemia in 1600. Tycho’s sudden
death in 1601 left Kepler in a position to analyze the motions of the planets as an imperial mathematician to the Holy Roman Emperor Rudolph II. He began
by studying the motion of Mars and soon abandoned the 2001-year-old belief in the circular and uniform motion of the planets. Also, he recognized that the
planets are kept in their orbits by the gravity of Sun but could not include this force into his formulas (this did Isaac Newton).
His main discoveries are now recognized as Kepler’s three laws of planetary motion (Tab. 4.1, 59):
1 The orbits of planets (light objects) are ellipses with the Sun (massive object) at one focus.
Ellipse is a geometric place of points their sum of distances from two points called foci (singular: focus) is constant. The eccentricity e is a measure of
the extent to which an ellipse departs from a circle. It is given by the ratio c/2a where c is the distance between the focal points of the ellipse and 2a is
the length of the major axis (a refers to the major semi-axis). For a circle, the two foci merge, c = 0, and e = 0. Most planets have orbits with a low
eccentricity, i.e. almost circles, such as Venus 0.0068, Neptune 0.00858, Earth 0.0167, Uranus 0.0461, Jupiter 0.0484, Saturn 0.05565; higher
eccentricities have: Mars (0.093377), Mercury (0.205628) and Pluto (0.249). Mutual gravitational influence of bodies orbiting around a common
massive body (Sun) usually results into a gradual reduction of eccentricity (making the eccentricity vary over a long period; e.g., the Earth’s
eccentricity varies between 0.005 to 0.06 in a period of about 100,000 years). This has been observed on rings of jovian planets (TG-p. 13) and may
be applicable to the orbiting of stars (not open clusters) in galaxies (TG-p. 20).
2
A line from the planet (light object) to the Sun (massive object) sweeps over equal areas in equal
intervals of time (Fig. 4-10, 58).
The motion of a planet (light object) on an ellipse is not uniform: its speed is inversely proportional to the distance from the massive object. Only the
motion on a circle is uniform (the speed is constant because the distance is constant).
3
Part 1: Earth + Sky, Kepler’s+ Newton'‘ laws.
Matter + radiation, astronomical tools
3
ASTR-100, «EDC»
printed: : 7-May-17, 10:08h
4
A planet’s orbital period squared is proportional to its average distance from the Sun cubed:
P2 = a3 .
The units for both quantities must be consistent; the simplest units refer to the Earth’s orbit: orbital period in the Earth’s years, the distance
in Earth’s to Sun distances, i.e. in astronomical units, AU. Because the average distance of the planet (light object) from the Sun (massive
object) equals the major semi-axis, the orbital period is independent of the minor semi-axis. For example, a circular orbit has the same
orbital period as an elliptical with the major semi-axis equal to the circle radius.
Newton’s laws of motion and gravity (64 - 66) http://userwww.sfsu.edu/~rsauzier/Newton.html
Sir Isaac NEWTON (1642 - 1727), English mathematician and natural philosopher (physicist), perhaps the greatest scientist that ever lived. His most
important discoveries were made during two-year period from 1664 to 66, when the university (Cambridge) was closed and he retired to his hometown of
Woolsthorpe. At that time he discovered the law of universal gravitation, began to develop the calculus, and discovered that white light is composed of all
the colors of the spectrum. These findings enabled him to make fundamental contributions to mathematics, astronomy, and theoretical and experimental
physics. He summarized his discoveries in terrestrial and celestial mechanics in his Philosophiae naturalis principia mathematica [1687].
Newton’s law of gravity (66):
F = -GMm/r2
where F is the force of gravity between
two masses (M and m) at a distance r; G is the gravitational constant 6.6710-11 Nm2/kg2.
This inverse square relation (Fig 8.4, 149) shows that intensity of fields (such as magnetic, electric and
gravity fields) and of energy, spreading from one point homogeneously to all directions (e.g. radiant
energy such as light) is inversely proportional to the square of distance because the dissipation of the
fields and energy is directly proportional to the square of distance.
Starlight & Atoms (6, 102-121)
ATOM (from the Greek a-, not + tomos, part, volume [temnein = to cut]: “not splitable”) is the smallest unit of matter no
more splitable by weak physical (mechanical) means. Atoms of the same kind form simple substances, elements. There are
only a few more than 100 elements, each defined by specific atoms. The approximate diameter of an atom is 10 -8 centimeter.
Each atom consists of a nucleus and shell(s) around, separated by extremely large empty space (104).
The nucleus represents the most of the atom’s mass; it consists of a specific number of +charged protons
and a similar or greater number of neutrons (only hydrogen, defined by a single proton in the nucleus, has usually no
neutron in the nucleus). The number of protons in the nucleus defines the element = atomic number [Z].
The number of protons in the nucleus allows the atom to carry the same total number of electrons in the shell(s). Each
electron bears the same amount of electric charge as each proton but with the opposite (negative) sign. This is why the atoms
in which the number of (negatively charged) electrons equals the number of (positively charged) protons are electrically
neutral from outside. Each electron takes a specific position (energy level, shell/sub-shell, orbit around the nucleus), which
controls the chemical properties and activity of the element.
Temperature corresponds to the kinetic energy of vibration of atoms or molecules per atom or molecule. At absolute zero temperature (-273.15°C = 0 K [K
stands for kelvin] = -459.67°F) there would be no vibration of the matter particles and the matter could not exist: this is why also the absolute zero
temperature can not exist, it may be approached only.
If receive energy (106 - 7), the electrons jump from a lower to a higher energy level (orbit); then they
jump immediately back to the original level, and release that energy in form of radiant energy, photon,
which is considered the electromagnetic (further abbreviated elmag) radiation unit (78). The photon
energy is directly proportional to frequency and inversely proportional to wavelength of the elmag
radiation (78-9). Due to the above-absolute-zero-temperature, any object radiates elmag radiation: the
wavelength of the maximum intensity radiation is diagnostic for the object’s temperature (black body
radiation, 108, Reasoning with Numbers 6.1, Fig. 6.6; Balmer series thermometer, 109, 111-4).
Wavelength (and the inversely proportional frequency) is the fundamental property of the elmag
radiation (78). Twelve kinds of elmag waves are recognized
The terminology (such as that in the Fig. 5.2, 79) is not consistent. Some expressions, such as FM & AM (frequency & amplitude modulation), are not
related to wavelength but to the method of coding information; other expressions describe frequency, such as UHF [ultra high frequency] and VHF [very
high frequency]). Below is a list of twelve consistent elmag radiation types:
Longest wavelength, lowest frequency:
1
2
3
4
long radio waves
medium radio waves
(AM)
short radio waves
very short radio waves (FM)
5
6
7
8
ultra short radio waves (TV)
microwaves (radar)
millimeter waves (MW)
infrared (IR) light
9
10
11
12
visible light
ultraviolet (UV) light
X-rays
gamma rays
Shortest wavelength, highest frequency
Within the range of visible (visual) light - six main colors can be distinguished:
(longest wavelength:) red, orange, yellow, green, blue, violet (shortest wavelength)
Elmag radiation forms by accelerating electric charge. Due to the natural frequency of radiating objects,
long elmag (radio) waves are generated by alternating (high frequency) electrical field on relatively
large objects, antennas; much shorter elmag waves, visible & invisible light, form by accelerating
electrically charged particles of atomic and subatomic size; even shorter elmag radiation (X and gamma
rays) forms by strongest acceleration of subatomic particles (atomic nuclei).
Three main types of objects generate elmag radiation with various wavelength/frequency:
objects
generated elmag radiation
a Antennas
radio waves up to shortest microwaves
b electrons, atoms, molecules and ions
infrared light (+microwaves) through ultraviolet light
c atomic nuclei, high energy electrons
X- through gamma rays
Similarly, elmag radiation passes only those objects their size is smaller than its wavelength. The
atmosphere allows only two narrow wavelengths (bands) of the elmag radiation to pass and reach the
Earth’s surface (two “atmospheric windows”, 79, Fig. 5-2):
a Visible light
b shortest radio waves (centimeter through about 1 meter wavelength)
4
Part 1: Earth + Sky, Kepler’s+ Newton’s laws.
Matter + radiation, astronomical tools
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The spectral (wavelength) analysis (of elmag radiation) can provide three main results at least
(other ones - see TG p. 17-18):
1) chemical composition: diagnostic wavelengths (emission/absorption light), each specific to a certain
atom’s electron, define elements; their intensities give percentages of each element (117 - 8);
2) temperature: by the wavelength (UV to IR light) of maximum intensity (black body radiation: red
objects are “cool”, blue ones “hot”; 108) and by the intensity of the Balmer series wavelengths (111,
114); (ultraviolet to infrared light);
3) radial velocity according to the Doppler’s effect (115-7, Reasoning with Numbers 6.2, Fig. 6.11), by
shortening or stretching of the wavelength of element spectrum (“blue” or “red” shifts denote the
changed position of the wavelength recorded as a line, either toward the blue or red margins of color
spectra, i. e. toward the shorter or longer wavelength respectively). The Earth orbiting mean speed
around the Sun is 30 km/sec (29.865 km/sec); thus the spectral shifts 6 months apart are due to the
Earth’s speed difference of ±30 km/sec = 60 km/sec of radial velocity.
4 Error! Reference source not found., ERROR! REFERENCE SOURCE NOT FOUND. JAN
06 Astronomical Tools (5)
The elmag radiation is the only information source about objects outside of the solar system, and still the
main source of observations within the solar system. Telescopes are the most popular and important
astronomic tools. Two types of optical telescopes that operate within the range of light (both visible and
invisible) are distinguished (80 - 2):
a) Reflectors (use one or more mirrors for objective): shorter, largest diameter (easier produced), no
chromatic aberration (except for an eyepiece which consists of lenses; used in most telescopes);
b) Refractors (use one or more lenses for objective): longer, limited diameter possible to produce,
chromatic aberration.
Review for the Test 1 (Test 1 to be Error! Reference source not found., 31 Jan 06).
Chapter
page
2: Position of an object on the sky - two methods.
11, 18; TG p. 1
Magnitude and brightness - relationship of their scales.
13, Fig. 2-6, 14, Tab. 2-1
3: Ecliptic - explanation.
22 - 3, Fig. 3.1, 3.2, 3.3; TG. p. 2
Seasons - explanation.
(23, Figs. 3.2 + 3.3), TG. p. 2
Lunar periods: orbital (sidereal) and phase (synodic) - explanation (their difference).
27 - 8; TG. p. 3
Tides - explanation; maximum high tide.
28 - 9; (TG. p. 3)
Solar & lunar eclipses, explanation of the frequency of their occurrence & visibility from the Earth (dependence on the observer’s position).
36 - 7; TG. p. 3
4: Kepler’s laws - explanation.
54 – 5, TG. p. 3
Newton’s law of gravity - explanation of the change of gravity force between two masses with distance.
61; TG. p. 3 - 4
5: Electromagnetic waves - sequence of their 12 wavelength types:
Long radio w., medium radio w., short radio w., very short radio w. (FM), ultra short radio w. (TV), microwaves (radar),
millimeter waves, infrared light (including millimeter waves), visible light, ultraviolet light, X-rays, gamma-rays.
(67), TG. p. 4
Three types of objects generating various electromagnetic waves.
TG p. 4
Property of the electromagnetic waves which controls their propagation past obstacles;
which condition is to be fulfilled (the wavelength must be longer than the obstacle’s size).
Two atmospheric windows for electromagnetic waves (visible light, shortest radio waves, 1 cm to 1 meter wavelength).
(67); TG. p. 4
Light telescopes - two basic types, their comparison (refractors, reflectors).
68 – 70, TG. p. 5
Visible light - explanation of colors and their arrangement in a spectrum.
67, Fig. 5.2, 80, Fig. 5.19; TG p. 4
6: Spectral analysis of stars - three major results from it, brief explanation of each.
(100 – 1), 104 - 5; TG. p. 5
Basic structure of atoms; their property defining an element (explanation); light emission & absorption (explanation).
91 - 98
5 Error! Reference source not found., 31 Jan 06:
TEST 1 (1h)
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SOLAR SYSTEM (16 through 19)
http//seds.lpl.arizona.edu/nineplanets/nineplanets.html
CD ROM: Views of the Solar System, National Science Teachers Association, Arlington, VA 22201-3000
The solar system includes Sun and diverse objects kept by gravity in orbits around Sun. Sun itself is a star,
and will be described later in this course (TGp 15, 122 – 43). The following body types are variously distributed
around the Sun:
a) Planets (with their >141 satellites) – orbits 0.4 to 40 AU from the Sun in a disk;
b) Asteroids – orbits centered at 2.77 AU from the Sun, mostly in a very broad ring;
c) Meteoroids - in the whole solar system (spherical) space (probably up to the van Oort belt);
d) Edgeworth – Kuiper’s Belt Objects (Gerard Kuiper) - orbits 38 to 200 AU from the Sun
(more than 400 KBOs
known today; the largest one, “2001 KX76”, has diameter 1200 – 1400km; Chiron & “QB1s”; Astronomy Aug 94, p. 26-33; Pluto is probably one of
the largest Kuiper’s disk members: Astronomy Dec. 97, p. 30); Pluto is a KBO (445-7): C. D. MURRAY & S. F. DERMOTT (CUP, 1999), Solar
System Dynamics, p. 14; 466-8;
e) Comets - in the whole solar system: short period comets up to about 40 AU in a thick disk, outside in a sphere (452-4,
459, 462-9);
f) Van Oort cloud – several trillions icy bodies (comets, without tails) within a hypothetical spherical zone 10,000 AU to
100,000 AU (long period comets) from the Sun (462-3).
The solar system is located in the Milky Way galaxy - the second largest star system in the close universe: it has
100 thousand light years in diameter, contains over 100 billion stars (252-76). Almost every celestial object
visible to our naked eyes is part of it, except Andromeda galaxy M31 (254), and two Magellanic Clouds (256,
285) in the southern sky, the galactic satellites. The solar system moves about 220 km/sec (Fig. 12-12, 263) in the
direction of Cygnus on circle with a radius of 10 kpc [32,600 light years] with an orbital period of 250 million
years.
Whereas the Sun has most of the mass, the planets with their satellites, asteroids, meteoroids, comets etc. have most of the angular momentum.
The solar system shows the following important properties, common to its bodies (367, Tab. 16-1):
1 Revolution (orbiting) of the planets with their satellites is nearly circular and nearly in the same
plane (3.4°: disk);
2 Revolution of all planets with almost all of their satellites, and rotation of most of the planets and
their satellites is counter-clockwise when seen from the north;
3 The age of the solar system is about 5 b. y. [billion years], currently 4.56 b. y. (measured on Earth,
meteorites, Moon; 367).
The planetary distances do not display an exact scheme, but, very approximately, the distance from the Sun of each next one is double of the previous
distance (Titius-Body law: C. D. MURRAY & S. F. DERMOTT (CUP, 1999), Solar System Dynamics, p. 5 – 9, Tab. 1.1, p. 6).
A few EXCEPTIONS (referring to the first two paragraph-#s above):
1a Excessive inclination to the ecliptic:
Pluto (17.2°), Mercury (7°);
1b Excessive eccentricity:
Pluto (0.25), Mercury (0.21), Mars (0.09);
2a Clockwise (retrograde) revolution (orbiting):
Triton (Neptune’s satellite),
Charon (Pluto’s satellite), 4 outermost satellites of Jupiter and one outermost satellite of Saturn;
2b Clockwise (retrograde) rotation (spinning on axis):
Venus, Uranus and Pluto.
Origin of the Solar System (356 - 9, Fig. 16-1)
According to the solar nebula theory, the solar system formed from a solar nebula about 4.6 by. ago.
Originally, about 5 by. ago, the solar nebula was a cloud of gas and dust - a fragment of an interstellar
gas cloud with about twice of its present total mass. A supernova explosion within 60 light years (18 pc)
away triggered the formation: the shell of gas ejected by a supernova could compress the surrounding
gas clouds. Approximately 5 main stages may be recognized (compare: 368 – 75):
1
Dust grains grew by condensation (atomic clustering such as in snow flakes) and accretion (such as snow ball rolling: the sticking together of solid
particles by carbon compounds and static electricity) and formed small planetesimals (diameter about a centimeter and larger objects). Gases + dust
are kept by a common gravity at the center into the space of spherical shape.
2
While the smallest dust grains were stirred up by the turbulent motion of gas, the planetesimals collapsed into the plane of the solar nebula about
0.01 AU thick– most of the material occurs in the space of a disk shape.
3
Gravitational instability broke the rotating disk of particles into small clouds, further concentrated trillions of the small into large planetesimals and
helped them coalesce into objects up to 100 km in diameter (large planetesimals).
4
The largest objects which exceeded this size, called protoplanets grew fastest by strongest gravity sweeping more and more material. Parallel motion
(the average orbital velocity in the solar system is about 30 km/sec) made head-on collisions (they would have pulverized the material) very
improbable: they merely rubbed shoulders at low relative velocities. The gravity of largest bodies may have been able to retain the fragments
produced in collisions, forming a layer of crushed rock which may have been effective in trapping smaller bodies. When massive enough, they
trapped some of the original nebula gas to form primitive atmospheres.
5
Inner protoplanets changing into true planets were subject to melting due to the terrific amount of energy given up by infalling material. Then the
material differentiated according to density: metals such as iron & nickel concentrated in core, lighter silicates float to the surface); gases released
from planets' interior formed the first atmosphere rich in carbon dioxide and water vapor (outgassing, 372).
As soon as the Sun became a luminous star, it began to clear the nebula blowing gas away and removing particles that had not become part of planets by
radiation pressure and solar wind (flow of ionized hydrogen and other atoms at about 600 km/sec); also the planets have been sweeping up the space debris.
This nebula clearing had been accomplished during the first billion years, planet building ended about 4 billion years ago.
The heating from the solar system’s center (the Sun) outwards resulted into chemical evolution and differentiation of the solar nebula. The temperature
decreasing from the nebula’s center outwards controlled the condensation sequence (369, Tab. 16-3): the inner planets condensed from high density
material with high melting points, such as metal oxides and pure metals; middle distant planets condensed from medium density materials with medium
melting and vaporization point, such as iron-magnesium silicates and aluminosilicates, and sodium, calcium + potassium aluminosilicates (Tab. 16.3, 369;
“silicates”, “feldspars”); in the cool outer region the lightest materials with the lowest melting and vaporization point condensed, such as ices of water,
carbon dioxide, ammonia, methane and nitrogen.
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Error! Reference source not found., 2 Feb 06EARTH-LIKE (INNER) PLANETS (17, 378 - 402):
Mercury, Venus, Earth and Mars
relatively small; as the Earth: composed largely of silicate rock (stony), similar densities; inner orbits, rotate
slowly on their axes. Among their satellites, the Moon is the only one of any appreciable size; the two satellites
of Mars are only a few km across (they are probably captured asteroids).
MERCURY (395-7)
Large metallic (iron + nickel) core (caused the greatest density; 395, 368, Celestial Profile 4, 395)
formed by meteoritic bombardment during the first billion years; this bombardment strongly heated and
expanded Mercury by about 10%; later the interior cooled and shrank; lobate scarps (Fig. 17-10, 396) up
to 3km high and 500km long formed. Weak magnetic field suggests the core is partially liquid (sulfur
impurity could lower the melting temperature). The tidal interaction with the Sun has caused 2 orbital
periods (each 87.969 days) to equal 3 axial rotations (each 58.646 days): spin-orbit coupling. Similar to
the Moon (black: albedo is 0.067%). No atmosphere, very hot days (300°C, max. 430°C, 700K), very
cool nights (-183°C, 90K); eccentric + inclined orbit; phases. 0 satellites. Astronomy, November 1988, 22 - 35.
http://www.seds.org/nineplanets/nineplanets/mercury.html;
VENUS (397 – 403)
David H. Grinspoon: Venus revealed; Addison Wesley Longman Inc., 1997
Atlas of Venus, by Peter CATTERMOLE & Patrick MOORE, Cambridge Univ. Press (http://www.cup.org), 1997, 160 pages; $29.95
Its diameter (12,104 km) and interior (core, mantle, & crust) are similar to those of the Earth but other
properties are very different. The strongest atmosphere (90 bar, 397) compensates temperature
variations, 96% is carbon dioxide, causes green house heating to 472°C; far more heavy hydrogen
(deuterium), 75-times more argon than on the Earth; variable content of sulfur dioxide; water deficiency
(0.01 - 0.1%); layered, white clouds of sulfuric acid (45km to 60km above the surface) completely hide
the surface (the yellowish tinge due to sulfur) cause the highest reflectivity from all planets (albedo .76).
Winds increase with altitude: at surface almost no wind (about 2 meter/second only), at 40km - 60km to
70 - 130 meter/sec. Retrograde (clockwise) slow rotation (243.01 days) tidally locked to the conjunction
with the Earth (orbital period: 0.61515 years = 224.68 days); active volcanism and limited horizontal
crust motion (folding) similar to plate tectonics (399-403); phases; 0 satellites.
Spacecraft Magellan launched 4 May 89 (Astronomy, Apr 89, 26-32, Apr 92, 20, 24-26) explored Venus by three 243-day (8 months)-long high resolution
radar imaging cycles (each consisted of 1000 polar highly elliptical orbits Aug 90 - 25 May 93): see pictures in Sci. Am., Oct 90, 11; The Planetary Report,
11/91, No. 3/May, Jun 8-13. Since 25 May 93, the 3 months were used for its aero-breaking to reach a low-altitude (200-600km) orbit which will make
possible a fifth cycle, of high-resolution gravity mapping (Astronomy Sep 93, 20). Venus is the evening star in Jun-Jul 05; http://www.spaceweather.com/.
EARTH (381 – 95)
http://bang.lanl.gov/solarsys/earth.htm
The largest Earth-like planet (12,756 km diameter). Partially liquid metallic (iron + nickel) core;
medium magnetic field; soft mantle; Moon’s (and Sun’s) tidal effects on water, air and on the main
body; the friction along major discontinuities within the main body is probably responsible for heating of
the subsurface crust & mantle which causes magmatism and volcanism; active plate tectonics; the only
planet with liquid water (which is one of the most important conditions of life): in oceans, glaciers,
lakes, rivers and clouds. The earlier atmosphere had no free oxygen; last 400 million years: nitrogen,
oxygen & argon atmosphere, carbon dioxide (recently only 0.035% CO2, which enables iced polar caps
& high mountain glaciers almost as during a few ice ages); 1 bar pressure. Mean year temperature 15°C
= 59°F; seasons due to equator-to-orbit tilt (23.5°); strong weathering, erosion & mountain formation
have erased most of the meteoritic cratering (only the youngest impact craters, up to 20 million y. ago,
can be recognized); well developed plant & animal life; 1 satellite. Early Earth - see Astronomy Jun 89.
The Earth & Moon interaction slows the Earth's rotation by about 2 milliseconds per century. 900 million years ago there were 481 18-hour days in a year.
MOON (387-95): diameter: 3,476km; mean distance from the Earth: 384,402 km; rigid interior; its crust is 40-60km thick
on the near side, 150km on the far side; most craters are meteoric (impact), few are volcanic. Because of the absence of
atmosphere and surface water the oldest surface features have been preserved and subject only to extremely slow wearing by
micro-meteorites and solar wind. Although geologically inactive at present, its surface shows signs of having once melted and
of having experienced many volcanic eruptions 3.2 - 4.3 billion years ago (basalt floods in marias) which overlapped the
oldest impact craters. Probably, a tidal heating (& hence volcanism) stopped since its rotation was tidally locked to the Earth
(it turns one side [with thinner crust] to the Earth only); phases; Moon’s & solar eclipses (TG-p. 2-3); 0 satellites. Moon’s
origin & evolution, large impact hypothesis (391-5): Astronomy Jul 94, 42-5. Annular solar eclipse: 3-OCT-05, Atlantic, Spain, Africa
(38). “Earthshine” yields clues to Earth's climate
http://spaceflightnow.com/news/n0104/18earthshine/
MARS (404 – 413)
Mars, The Story of the Red Planet, by Peter CATTERMOLE, Chapman & Hall 1993, 224 pp.; Astronomy Sep 93, 26-33, Dec. 93, 49-53
Internet: http://mpfwww.jpl.nasa.gov/mpf/marswatch.html http://mgs-www.jpl.nasa.gov/ Nat. Geogr., Feb. 2001.
Lowest density from the inner planets; 6,796km diameter (53% of the Earth’s d.). Thin atmosphere (7.4
mbar) can not compensate temperature variation which is due to both eccentric orbit (global seasons)
and the equator-to-orbit tilt (23°59'; hemispheric seasons). When Mars is closest to the Sun, surface
heating causes strong supersonic winds initiating fine silt storms which hide the surface during few
months: about 1/3 of the Sun radiation becomes absorbed be the clouds and the surface cools until the
winds calm and the atmosphere cleans. Temperature: yearly mean -43°C, min. winter -123°C (carbon
dioxide crystallizes), max. summer -+10°C; reddish due to hematite (highly oxidized iron: Fe2O3) which
could form by free oxygen only, but its atmosphere now almost lacks oxygen: 96% carbon dioxide, 2.5%
nitrogen, 1.5% argon (0.1% oxygen if any at all); similar to Earth in rotation period (24h37m23s) and
equator-to-orbit tilt; in the past: volcanic activity (Olympus Mons is the highest volcano in the solar
system, 407, Fig. 17.18; The Planetary Report, vol. 10/1990, 6/Nov-Dec), water erosion & deposition; more evidence of
water work (gullies, etc.) discovered recently; 2 small satellites (Phobos & Deimos, 411-2; captured
asteroids ?).
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Error! Reference source not found., 7 Jan 06:JOVIAN (OUTER) PLANETS (18, 418-47):
Jupiter, Saturn, Uranus, and Neptune
giants, low density, composed of gases (about 90% hydrogen and up to about 10% helium)
compressed to liquid form; they rotate rapidly on their axes, have 138 satellites and various types of
rings.
JUPITER (422 – 31)
Voyage to Jupiter by David Morrison & Jane Samz, NASA SP-439, 199 pages, 1980;
Internet: http://www.jpl.nasa.gov/galileo/Jovian.html
http://seds.lpl.arizona.edu/nineplanets/jupiter.html
Largest planet (11-times diameter, 1300-times volume, 318-times mass of the Earth) dominates the solar
system; low density (1.33 g/cm3); its average distance from Sun is 5.202561 AU; with Saturn, the fastest
rotation on axis (period 10 hours). Its atmosphere is in constant motion, driven by heat escaping from a
glowing interior as well as by sunlight. Energetic atomic particles stream around it, caught in a magnetic
field that reaches out nearly 10,000,000 km into the surrounding space, embracing the seven inner
satellites. From its deep interior through its seething clouds out to its pulsating magnetosphere (Fig. 182, 422), J. is a place where forces of incredible energy contend. Jupiter is evening star Jun - Jul 05.
Between July 15 and 22, 1994, Jupiter experienced a series of impacts of 20 fragments of the comet Shoemaker-Levy 9 (Astronomy, Oct 94, 40-45; see the
Report from Galileo probe in Astronomy, Oct. 95, p. 34-41, April 96, p. 42-5). The famous Italian astronomer Giovanni Cassini recorded a hit on Jupiter:
the spot evolved between December 5 and 23, 1690 (Astronomy May 97, p. 34+36).
At its birth, J. shone like a star. The energy released by infalling material from the solar nebula heated
its interior, and the larger it grew the hotter it became (when the nebular material was finally exhausted,
J. had probably a diameter more than ten times its present one, a central temperature of about 50 000 K,
and a luminosity about 1% as great as that of the Sun today). At this early stage, J. rivaled the Sun. Had
it been perhaps 70 times more massive than it was, it would have continued to contract and increase in
temperature, until self-sustaining nuclear reactions could ignite in its interior. If this had happened, the
Sun would have been a double star, and the Earth and the other planets might not have formed.
However, J. did not make it as a star: after a brief flash of glory, it began to cool. At first, J. continued to
collapse. Within the first ten million years of its life, the planet was reduced to nearly its present size,
with only a few percent additional shrinkage during the past 4.5 billion years. The luminosity also
dropped as internal heat was carried to the surface by convection and radiated away to space. After a
million years J. emitted only one-hundred thousandth as much radiation as the Sun, and today its
luminosity is only one-ten billionth of the Sun’s. Jupiter’s internal energy, although small by stellar
standards, has important effects on the planet. About 108 Gigawatts (1017 watts) of power, comparable to
that received by J. from the Sun, reach the surface from the still-luminous interior. The central
temperature is thought to be about 30,000 K, sufficient to maintain the interior in a molten state (J. is
probably an entirely fluid planet, with no solid core whatever). Because of its great mass, J. has been
undiscriminating in its composition. All gases and solids available in the early solar nebula were
attracted and held by its powerful gravity. Thus it has the same basic composition as the Sun, with both
bodies preserving a sample of the original cosmic material from which the solar system formed: 90%
hydrogen, 10% helium (ratio 0.11 close to that of the Sun, 0.12), traces of methane (CH4), ammonia
(NH3), water (H2O), ethane (C2H6), germane (GeH4), acetylene (C2H2), phosphine (PH3), carbon
monoxide (CO), hydrogen cyanide (HCN) and carbon dioxide (CO2).
Uppermost clouds are probably ammonia cirrus, layers of ammonium hydrosulfide (NH4SH), and water
probably exist at deeper levels. All these clouds are formed in the troposphere, the layer in which
convection takes place. The top of the ammonia cloud deck is thought to have a pressure of about 1
atmosphere and a temperature of about -113°C. Ammonia cirrus is white, yet Jupiter’s clouds display a
spectacular range of colors, perhaps due to trace impurities of organic polymers, formed from
atmospheric chemicals such as methane and ammonia that have reacted with lightning, are responsible
for the oranges and yellows. The color of the Great Red Spot (GRS) could be caused by red phosphorus
(P4). According to this theory, phosphine (PH3) from deep in Jupiter’s atmosphere is brought to high
altitudes by upwelling of the GRS. Sun’s ultraviolet light, penetrating the upper reaches of the GRS,
splits the phosphine molecules, and, through a series of chemical reactions, converts the phosphine into
pure phosphorus. However, this theory fails to explain the color of the smaller red spots which are not at
such high altitudes as the GRS (which is the highest and coldest of Jupiter’s visible clouds), so it is
unlikely that UV-light could react with any phosphine in these areas to produce red phosphorus. Various
forms of elemental sulfur might be responsible for the riot of color we see on Jupiter. Sulfur forms
polymers (S3, S4, S5, S8) which are yellow, red, and brown, but no sulfur in any form has been detected
on Jupiter. There are low temperatures over bright zones and higher temperatures over dark belts; a cold
area is visible up to the top of the troposphere above the GRS (this feature disturbs apparently the
atmosphere to very high altitudes). The minimum temperature of about -173°C occurs at a pressure level
of 0.1 atmosphere. Above this point lies the stratosphere, in which temperatures increase with altitude
as a results of sunlight absorbed by the gas or by aerosol particles resembling smog. At 70km above the
ammonia clouds, the temperature is about -113°C. Above this level, the temperature stays approximately
constant, although at extreme altitudes the temperature again rises in the ionosphere. Above this level,
the temperature stays approximately constant, although at extreme altitudes the temperature again rises
in the ionosphere.
The Voyager pictures reveal a planet of complex atmospheric motions. Spots chase after each other, meet, whirl around, mingle, and then split up again;
filamentary structures curl into spirals that open outward; feathery cloud systems reach out toward neighboring regions; cumulus clouds that look like
ostrich plumes may brighten suddenly as they float toward the east; spots stream around the GRS or get caught up in its vortical motion - all in an incredible
interplay of color, texture, and eastward flows. Such changes can be notices in the space of only a few Jovian days. On a broader time scale, greater
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changes on the face of J. can be seen. Features drift around the planet; even the large white ovals and the GRS slide along in their respective latitudes. Belts
of zones intrude upon each other, resulting in one of the banded structures splitting up or seeming to squeeze together and eventually disappear. Small
structures form, then die. The largest spots may slowly shrink in size, and the GRS itself changes its size and color. The Jupiter of Pioneers 10 and 11 was
quite unlike the planet seen by Voyager 1. At the time of the Pioneer exploration, the GRS, embedded in a huge white zone, was more uniformly colored,
and pale brown bands circled the northern hemisphere. In the intervening years, the south temperate latitudes have changed completely, developing the
complex turbulent clouds seen around the GRS by Voyager 1. Yet, even between the two Voyagers, Jupiter appeared to be undergoing a dynamic “facelift”. At a quick glance, Voyager 2 photographs showed the visage that had been familiar since early in 1979, but a closer look showed that it is not quite
the same. The white band below the GRS, fairly broad during the first fly-by, had become a thin white ribbon where it rims the southern edge of the Spot.
The turbulence to the west of the GRS had stretched out and become “blander” than it was before. Small rotating clouds seemed to be forming out of the
waves in this region. The cloud structure that had been east of the GRS during the Voyager 1 fly-by spread out, covering the northern boundary and
preventing small clouds from circling the huge red oval. The GRS itself also changed. Its northern boundary seemed - at least visually - to be more set off
from the clouds that surround it, and the feature appeared to be more uniform in color, perhaps reverting back to the personality it had in Pioneer days. The
most obvious features in the atmosphere of J., after the banded belts and zones, are the GRS and three white ovals. These have often been described as
“storms” in Jupiter’s atmosphere. The ovals are about the size of the Moon, and the GRS is 2.5× larger than the Earth. Voyager has revealed that in many
respects the white ovals, which formed in 1939, resemble their ancient red relative.
All four spots are southern hemispheric anticyclonic features that exhibit counter-clockwise motion; hence they are meteorologically similar. Other smaller
bright elliptical and circular spots also exhibit anticyclonic motion, rotating clockwise in the Northern Hemisphere and counter-clockwise in the Southern
Hemisphere. In general, these features are circled by filamentary rings that are darker than the spots they surround. Hints of interior spiral structure can be
seen in some of these spots. All the elliptical features in the Southern Hemisphere lie to the south of the strong westward-blowing jet streams. The spots tend
to become rounder the closer they are to the poles. Along the northern edge of the equator are number of cloud plumes, which appear to be regularly spaced
all around the planet. Some of the plumes have been observed to brighten rapidly, which may be an indication of convective activity; indeed, some of the
plume structures seem to resemble the convective storms that form in the Earth’s tropics. The plumes travel eastward at speeds ranging from about 100 to
150 meters per second, but they do not move as a unit. The most visible cloud interactions take place in the region of the GRS. Material within the GRS
rotates about once every six days. The GRS is a region of atmospheric upwelling, which extends to very high altitudes; however, the divergent flow
suggested by this upwelling seems to be very small - one bright feature was observed to circle the GRS for sixty days without appreciably changing its
distance from the spot’s center. During the Voyager 1 fly-by, spots were seen to move toward the GRS from the east, flow along its northern border, then
either flow on to the west past the GRS or into the outer regions of its vortex.
Despite all the turbulence in Jupiter’s atmosphere - this ever-changing chaotic mixture of cyclonic and
anticyclonic flows, of ovals and filaments, of reds, browns, and whites - a pattern may be emerging:
there is an underlying order to the seemingly random mixing of patterns in the Jovian atmosphere. First,
the changes are in some sense cyclic. Another order is in the alternating belts and zones: the cloudcovered zones are probably regions of rising air, and the belts are regions of descending air (slow
vertical circulation); in addition, there are horizontal or zonal flows - regular distribution of eastward
and westward jets around equator (speed ranges from -80 through +100 m/sec.). The long-time
persistence remains a mystery. The recent series of about 20 impacts of the broken comet ShoemakerLevy 9 in July ‘94 was recorded both few hours after the impacts from the Earth + Hubble’s Space
Telescope, and directly from the spacecraft Galileo; after the unique data will be processed, new insights
are expected.
Voyagers recorded several meteor trails in the dark side of Jupiter’s atmosphere. Traveling at roughly
60 km/sec as they entered, these fireballs brightened quickly and survived for about 1000 km before they
died. Frequently tremendous auroras (both in ultraviolet and visible light) in polar regions were
observed. The ultraviolet auroras are created when high-energy particles from the Io plasma torus spiral
toward J. on magnetic field lines. Clusters of lightning bolts - indicative of electrical storms - were also
discovered on Jupiter’s night-side, independent of latitude. Voyager 1 viewed 19 superbolts of lightning
simultaneously, Voyager 2 eight ones. Radio emissions (whistlers) accompany the lightning discharges.
Deep in the interior of J., the pressures are so great that liquid hydrogen becomes an electrical conductor, like a metal. Currents driven by the rapid rotation of the planet are thought to flow in this
metallic core. The result is a magnetic field that penetrates the space around J.. The strength of the
Jovian magnetic field is about 4000 times greater than that of the Earth. The di-pole axis is not at the
center of J. but offset by about 10,000 km and tipped by 11° from the axis of rotation. Each time the
planet spins, the field wobbles up and down, carrying with it the trapped plasma of the radiation belts.
The most gargantuan Jovian feature is its magnetosphere, which envelops the satellites and constantly
changes in size, pumping in and out at the whim of the solar wind. Its borders in the upwind solar
direction lie between 50 and 100 Jovian radii from J.. Downwind, away from the Sun, the
magnetosphere extends much farther, perhaps as far as the orbit of Saturn. Just inside of the
magnetosphere is the “hot spot” of the solar system: a 300 - 400 million degree plasma: “Even the
interior of the Sun is estimated to be less than 20 million degrees - the temperature of that Jovian plasma
is the highest yet measured anywhere in the solar system. Fortunately for Voyager, this region of
incredibly hot plasma is also one of the solar system’s best vacuums. The spacecraft was in little danger
because the bow shock of the magnetosphere protects this region from the solar wind, and most of the
particles in Jupiter’s magnetosphere are held in much closer to the planet.
3 bands of dark RINGS of dust around Jupiter (425, 428)
They extend from the upper atmosphere to a distance of 53,000 km above the cloud tops, 1.8 Jupiter’s radius
from its center; the main rings, however, are much narrower, spanning from 47,000 km to 53,000 km above
Jupiter. There are two main rings, a 5000 km wide segment, and a brighter, outer 800 km segment. The thickness
is less than 30 km, probably under 1 km. Apparently the individual particles that make up the rings are widely
dispersed (Pioneer 11 traversed the ring in 1974 with no obvious consequences); they are as fine as cigarette
smoke. The ring particles move around Jupiter in individual orbits, circling the planet in 5 - 7 hours.
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62 SATELLITES of Jupiter (428 – 30)
Satellites of Jupiter by David MORRISON (Inst. of Astron, Univ. Hawaii, Honolulu, HI; Editor),
Univ. of Arizona Press, Space Science Series, Tucson, AZ 1982, 974 pages
recent comprehensive results from the spacecraft Galileo and Hubble’s Space Telescope (HST):
Galileo turns geology upside down on Jupiter’s icy moons; Science (AAAS), vol. 274, 18 Oct. 96, p. 341; also p. 377 - 412;
http://www.jpl.nasa.gov/galileo/
http://www.planetary.org/html/news/articlearchive/headlines/2001/saturnmoons.html
The Jovian system is dominated by the 4 large Galilean satellites, which vary in size from just smaller
than Moon (Europa: 3130 km; density 3.04 g/ccm) to nearly as large as Mars (Ganymede: 5276 km;
density 1.93 g/ccm); the remaining two ones are Io (3640 km; density 3.55 g/ccm) and Callisto (4840
km; density 1.83 g/ccm). They are in nearly circular orbits in the same plane as the Jupiter’s equator, and
all lie within the inner magnetosphere of J., where they interact strongly with energetic particles and
plasma. Io is the most volcanically active body of the Solar System.
Laplace (Marquis de L.; title of Pierre Simon. 1749 – 1827. French mathematician & astronomer.) resonance of the orbital periods of
Io, Europa and Ganymede generates orbital alteration and tidal heating (378; particularly on Io)
resulting from non-circular motion in enormous gravitational field of Jupiter. The energy input (Io: 107 108 MW, Europa 105 - 106 MW) depends on the resonant coupling; as the resonance has evolved, the
heating has also changed with time. Tidal distortion into a prolate spheroid caused the Galilean satellites
to rotate synchronously with their orbital periods (as on our Moon). If these satellites were in exactly
circular orbits, the tidal bulge would be fixed and there would be no tidal flexing and therefore no
heating. Bulge on Io would be 8 km high.
Despite the fact that Io should undergo more intense meteoritic bombardment than any other satellites,
due to the 'focusing' effect of Jupiter’s gravitational field, not one impact crater can be found because the
surface is very young and geologically active. The volcanic plumes rise 70 to 280 km above the surface,
extensive lava flows and volcanic vents were discovered too. The lava consists of molten sulfur; the
volcanism is driven by sulfur dioxide. Polymers of sulfur are responsible for the striking red and orange
color; extensive white areas consist of sulfur dioxide snow. A small body such as Io, which is only
slightly larger than the Moon, should have long ago lost the heat generated during its accretion, and
negligible heat from radioactive decay.
However, the other Galilean satellites cause perturbations in Io’s orbit so that its distance from Jupiter
varies slightly (422,000km; orbital period: 1.769 days; no orbital eccentricity, negligible orbital
inclination; see A14). Jupiter’s gravitational field is so strong that even these small changes cause great
tidal distortions of Io, and thus produce sufficient heating of the interior for all the volcanic activity. Io
appears to consist of a molten silicate interior, just possibly with a solid core, overlain by a layer of
liquid sulfur several kilometers deep. Above this is a layer consisting of a mixture of solid sulfur and
liquid sulfur dioxide (SO2) covered by a solid crust of sulfur and sulfur dioxide. A number of localized
warm regions were found, the most dramatic being just south of the volcano Loki: a strange U-shaped
black feature of 17°C (room temperature), in contrast to the surrounding surface at -146°C. Perhaps the
dark feature was some sort of lava lake, either of molten rock or molten sulfur. The melting point of
sulfur is 112°C. Probably, there was a scum of solidifying sulfur on top of the “lake”.
Europa is the next satellite out from J. It is quite similar to Io (and Moon) in size and density, has a
weaker tidal heating (105 - 106 MW) but otherwise it is unique in the Solar System: only a few small
impact craters have been found; the rest of the surface is incredibly smooth. A network of straight,
curved or irregular dark markings covers the whole surface, and these range from less than 10 km to
about 70 km in width. There are also randomly located dark spots, but all these markings appear to have
quite negligible vertical height, so that the satellite has been described as 'a billiard ball covered in
scribbles from a felt-tipped pen'. Even stranger is yet another network of markings, this time faint and
light-colored, quite independent of the dark ones, and covering the whole satellite. These are only about
10 km wide, and they do show some vertical relief, although this is less than a few hundred meters.
However, the most surprising thing about these ridges is that they are not straight: they run across the
surface in a regular series of curves or scallops, ranging from about 100 to 300-400 km across. Parts of
the surface are covered with apparently freshwater frost, as well as traces of sulfur (almost certainly
derived from Io). However, there is fewer sulfur than would be expected, which may well indicate that
some has been buried beneath fresh frost deposits. These considerations, together with the lack of impact
craters, suggest that processes are still acting to smooth out the surface. Europa, like Io, is subject to
tidal forces, which could well maintain heating in the interior. Probably, a thick layer of water and ice
(perhaps about 100 km deep) covers a solid rocky core. Liquid water could escape to the surface through
the cracks and give rise to the frost deposits before the cracks themselves freeze over again, perhaps after
a few years. The low rigidity of the icy crust would account for the lack of impact craters. The darker
markings could well have been formed when the underlying water layer contained some mixture of other
substances at an earlier period in the body’s history.
Ganymede, the largest satellite in the Solar System (diameter: 5,276 km), and Callisto both have lower
densities than Io and Europa - about 1.93 g/ccm. This suggests that they be both comprised of roughly
half rock and half ice. They are thought to have rocky cores surrounded by water or icy layers with icy
crusts. The surface of Ganymede is very varied. The oldest regions consist of dark plains, one of which,
Regio Galileo, is as much as 4 000 km across and preserves signs of a major impact in a series of low
ridges (about 100 m high) spaced about 50 km apart. All this old terrain appears to have been fractured
into separate blocks, some of which have been displaced, and some completely replaced by younger,
lighter-colored material consisting of long parallel lines of valleys and ridges about 15 km across and
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1 km high. This 'grooved terrain' is highly complex in appearance, not only cutting into the old plains,
but also intersecting older areas of the same type, suggesting many mountain-building episodes. Still
other regions show rough mountainous terrain, and Ganymede’s surface seems to be the one place in the
Solar System to have undergone geological changes like those of the Earth’s plate tectonics. Some
craters appear relatively fresh, with bright haloes, presumably from ice or water ejected by the impact,
but most of the surface is actually very old. Crater counts suggest that the dark plains date back to about
4 billion years, and even the most recent grooved terrain seems to be about 3.5 billion years old - roughly
the same as the lunar highlands. The low relief probably results from a time when the interior was rather
warmer and the crust more plastic. Recent views from the spacecraft Galileo indicate signs of a possible volcanism.
Callisto (density 1.83 g/ccm) seems to posses an even thicker icy crust than Ganymede, and it is very heavily cratered.
However, all the craters are shallower than similar-sized ones on any other terrestrial planets. There are remnants of large
impacts, but they all have very little vertical relief. One, Valhalla, has a bright central region, about 600 km across, probably
representing the original impact crater, and is surrounded by an immense set of 'ripples' which makes its overall diameter
nearly 3000 km - far larger than any feature such as Mare Orientale on the Moon or the Caloris Basin on Mercury. It seems
certain that flow has occurred in the icy surface to obliterate many of the very old impact scars, and to reduce the height of the
remainder. Apart of this, however, there appears to have been very little true geologic activity on Callisto.
The next group of Jovian satellites consists of small, difficult-to-observe, objects (Lysithea, Elara, Himalia, and Leda).
They have similar orbits, varying in distance from J. between 11 and 12 million km (about 160 radii of J.). Like the outermost
group, they have orbits of high inclination; unlike the outer group, they move in proper, prograde direction around J. The
largest, Himalia (170 km in diameter) and Elara (80 km in diameter) are very dark, rocky objects, and it seems probable that
the others are similar.
The four outermost satellites (Sinope, Pasiphae, Carme, and Ananke), circle in highly inclinedn retrograde orbits,
distances from J.: 20 - 24 million km (290 - 333 radii of J.). These small bodies, none more than 30 km in diameter, require
nearly two years for each orbit. Probably, they are captured asteroids but nothing is known about their surface.
SATURN (431 – 7)
Second largest planet (9.45-times diameter of the Earth, 95 Earth masses); the lowest density of any
planet (0.70 g/ccm) indicating that much of Saturn is in a gaseous state; average distance from Sun is
9.551747 AU; with Jupiter, the fastest rotation on axis (period: 10h); tens of thousands rings; 17 larger
(+18 smaller) satellites (381) from which Titan is truly outstanding: intermediate in size (5150km
diameter) between Mercury and Mars, Titan (similar to Triton, the satellite of Neptune) is the only
satellite with thick atmosphere (1.6x thicker than Earth’s atmosphere) which consists of 85% nitrogen,
12% argon, 3% methane (possibly converted by Sun’s UV radiation into ethane & tarry organic
compounds which could be precursors of life), is opaque, with multiple layers of aerosols; surface is
completely hidden by a dense blanket of clouds 200 - 300 km above surface; its temperature is (-178°C)
almost certainly raised by some form of greenhouse effect. This temperature is close to that at which
methane is either solid or liquid, so that methane clouds in a nitrogen/methane atmosphere may be
raining methane down on to the surface. Radar echoes suggest that the surface consists both of
continents (formed by ices of water and carbon dioxide and rocks) and ocean of methane and ethane up
to 1 km deep. Iapetus, Saturn’s outermost large satellite, is tidally locked to Saturn and has a two-face
appearance: its leading side is black, its trailing side is white (Astronomy Dec. 97, p. 28, 30).
Interpretation of Saturn (& Jupiter’s) gases: The Planetary Report, vol. 10/1990, No. 6/NovemberDecember, p. 4-11. http://www.planetary.org/learn/solarsystem/moons.html
URANUS (437 – 42)
Uranus, The Planet, Rings and Satellites by Ellis D. MINER
(Jet Propulsion Laboratory, California Institute of Technology, Pasadena), Ellis Horwood Ltd, Chichester, England, 1990, 334 pages
Third largest planet (4-times diameter of the Earth, 14.6 Earth masses); the density is similar to that of
Jupiter (1.27 g/ccm); average distance from Sun: 19.21814 AU; it spins medium rapidly on axis (period
of rotation is 16.8h0.3h; Astronomy, May 1986, 10 [6-22]) which is more than 8° tilted below the plane
of its orbit, and thus retrograde; see Nat. Geogr. Magazine. Aug 86, p. 178-194; the magnetic field axis
is tipped 55° to the rotational axis, the total energy bound up in the Uranian magnetic field is about 1/10
that of the Saturn magnetic field, 1/400 that of Jupiter’s, and 50 times that of Earth’s magnetic field (the
presence of a strong and unusual magnetic field implies that Uranus contains some sort of circulating
conductive material, a “dynamo”); Uranus' overall density is considerably greater than Saturn’s, for
example, suggesting the planet has a molten silicate (“rock”) core about the size of Earth (13,000km in
diameter) enveloped in an 8,000km deep “ocean” composed primarily of water, and wrapped in an
11,000km thick hydrogen-helium atmosphere; currents in the water shell, driven by the heat of the
molten-rock core, could act as a dynamo for the magnetic field; 64 K atmosphere temperature; 10 thin
charcoal-black rings and hundreds of narrow, all-but-invisible ringlets; 27 satellites.
Miranda (369, Fig. 18-20b), the innermost moon, is a geologic enigma marked by several ovoids (389)
NEPTUNE (442 – 5)
Fourth largest planet: almost 4-times diameter of the Earth (Neptune’s equatorial diameter is 49,520 km,
Neptune’s volume could hold 57.7 Earths), 17 Earth masses; its low density is the highest from the Jovian planets (1.70 g/ccm). At an average distance of 4.5 billion km from the Sun, Neptune circles the Sun
once in 165 years; it spins on axis rapidly (slightly more than 16h). Neptune has a highly tilted (50° from
the rotational axis: similar to the 59° tilt of Uranus' dipole) and offset (by 0.4 of Neptune’s radius:
similar to the 0.3 Uranian radius offset) magnetic field (the magnetic north is in the southern
hemisphere). Its atmosphere is primarily hydrogen, helium, and methane. The methane gives the planet
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its lovely blue color Neptune’s cloud-tops show a surprising amount of variability, apparently due to an
energy source in its interior. While the large dark oval (its size is almost as the Earth), first seen in the
spring 1989, has remained relatively constant in position, a bright cloud to the north and east was seen to
separate from the dark spot. The strong winds on Neptune have different velocities at different latitudes,
as is the case for Jupiter (also for Saturn and slightly on Uranus). About three interrupted rings assumed
earlier (Astronomy, September 1987, p. 6-17) were confirmed together with a discovery of two
continuous rings during the Voyager 2 fly-by (the closest approach [4,850 km from cloud tops] 25
August 1989, 4:00h); in addition to the currently known 2 larger satellites (Triton & Nereid), the
Voyager 2 discovered 6 small moons probably interacting with the rings as the shepherd moons in
Saturn rings; the diameters of these moons are smaller than 600 km; they orbit close to Neptune: 52,000
km, 62,000 km, 73,000 km, & 117,650 km from the center of Neptune). Triton (Astronomy, February
1989, 20-6), orbital period 5.8768 days, the only large object in the Solar system with a retrograde
(clockwise) orbit; the orbit is circular and inclined 21o to the equator of Neptune, 355,200 km distant
from Neptune; mass: 9.310-4 Neptune (9.31019 metric tons), diameter 3,600km800km; surface
temperature 52 - 63 K; Voyager 2 discovered unexpected clouds casting shadows; relative stable
position of some of them compared with moving neighbor ones has been preliminarily explained as due
to a volcanism. Nereid, orbital period 359.4 days, orbital inclination 27.7o, extreme orbital eccentricity
(0.7545), diameter 940 km. The total number of satellites known to SEP-04: 13.
Results of the Voyager 2 fly-by 25 Aug 89 were published in: Newsweek, No. 36 4 Sep 89, 6-12; Aviation Week & Space Technology (McGraw-Hill Inc.),
No. 10, 4 Sep 89, 18-21, 60-64; Voyager Bulletin, Mission Status Reports (NASA, Jet Propulsion Laboratory, Calif. Inst. of Technology, Pasadena, CA;
phone recorded reports available by calling 818-354-0409; Public Information Office: 818-354-5011); Science, 15 Dec 89.
Future of the Voyager 2:
middle 1990:
its cameras, infrared detector and photopolarimeter turned off;
since then:
only fields and subatomic particles will be recorded;
Sep 1993:
Voy1 51AU, Voy2 40AU from the Sun; low frequency radio emissions detected from heliopause (interstellar/solar medium)
year 2010:
both Voyagers probably cross the heliopause (Astronomy Sep 93, 20);
year 2015:
probably silent;
after 42,000 y.:
it will come within 1.7 l. y. of the star Ross 248 (a cool red star, about 0.2 M _);
after 296,000 y.:
it will pass within 4.3 light years of Sirius, the dog star.
PLUTO - the outermost & smallest planet or a Kuiper’s Belt body? (445 –7);
Astronomy: Jul 86, 7-22; Jan 94, 40-47;
Alan STERN & Jacqueline MITTON, Pluto and Charon; Ice worlds on the ragged edge of the Solar System;
J. Wiley & Sons, N.Y., 1998; 223 pages; ISBN o-471-15297-8;
http://dosxx.colorado.edu/plutohome.html
http://bang.lanl.gov/solarphys/pluto.html
Pluto seems to be only slightly smaller (diameter: 2294 km; .002 Earth masses) than the Moon and to be
composed of methane & water ices mixed with rock (density 1.84 g/cm3; temperature 40 to 60 Kelvin = 233 to -213°C). Pluto’s orbit (its period = 247.7 years) is less circular and more highly inclined than
that of any planet in our solar system (17°9'3” to the ecliptic, i.e. more than double that of the greatest
planetary orbital inclination, Mercury: 7°). Its orbital eccentricity is 0.2484; its mean distance from the
Sun is 39.44 AU; since 21 January 1979 through 14 March 1999 Pluto was closer to the Sun than
Neptune: in 1989 it reached perihelion and was only 29.64 AU from the Sun; it ventures as far as 49.24
AU from the Sun at aphelion in the year 2112. At perihelion (when closest to the Sun), Pluto gets thin
atmosphere of nitrogen, carbon monoxide & methane. As Pluto moves farther from the Sun, its
atmosphere freezes, its surface gets white due to snow of methane. UV Sun radiation, over the years,
will turn it dark. Thus Pluto grows brighter as it moves away from the Sun. Pluto spins slowly on its
more than “horizontally” tilted (118°) axis: Pluto’s “day” is 6 E. days, 9 hours, 18 minutes. It has one
satellite, Charon: its orbit (similarly as its equator) is perpendicular to that of Pluto (Fig. 18-18, 446),
with the same orbital period as the Pluto’s day; therefore, for an observer on the Pluto’s surface, Charon
remains locked in the same position above the horizon and looks sixty times larger than Earth’s Moon.
Twice during each revolution of Pluto around the Sun, Charon’s orbital plane is edge-on to Earth; it was
during these times that we have seen Pluto and Charon eclipsing each other. Its recent eclipse cycle of 6
years, 1985-91, enabled to improve data on size & density of the both bodies and unique observations of
Pluto’s temporary atmosphere. Relatively to Pluto, Charon (about the half Pluto’s size) is the largest
satellites of the Solar system; thus, Pluto & Charon are almost a double (binary) planet, the common
center of revolution is between both the bodies. Pluto is the only planet, which has been not yet visited
by any spacecraft. Two special probes “Pluto Express” should be launched by NASA in 2001, to reach
Pluto at about 15,000 km distance in 2013, at an interval of about 6 months.
See: http://www.jpl.nasa.gov/pluto/ ; http://www.lpl.arizona.edu/pluto/ ;
http://spacelink.msf.nasa.gov/NASA.Projects/Planetary.Probes/Pluto.Fast.Flyby/ .
9 Th, 9 Jan 06:
METEOROIDS & METEORITES (452-458)
Meteoroids are small bodies derived from the asteroids or comets, and, similarly to them, they represent
samples of the original (unaltered) solar nebula. They eventually fall into Earth’s atmosphere and burst
into incandescent vapor about 80 km above the ground (shooting stars = meteors) because of friction
with the air. Most of them are produced by tiny bits of debris from comets (456-2, Fig. 19-3; meteor
showers Tab. 19.1, 414, A-12, 459). These are so small that they are vaporized completely in the
atmosphere and never reach the ground. Meteoroids, which survived the fiery passage, are known as
meteorites. During first two weeks of May 98 (peak May 4 - 5), meteor showers Eta Aquarids are famous for bright fireballs and long paths due to
their high speed of 65 km/sec (caused by Halley’s comet, similarly as the October Orionids): Astronomy May 98, p. 71.
Two broad categories can be distinguished: iron meteorites - chunks of a coarsely crystallized alloy of
iron and nickel (455, Fig. 19-2a), and stony meteorites (Fig. 19-2b) - silicate aggregates resembling
Earth rocks which appear never to have been heated to melting.
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Large crystals (Widmanstätten [Aloys von W., Austrian technologist, 1754-1849] pattern) of the iron meteorites suggest that
they cooled no faster than a few degrees per million years: their material could form within cores of large (ca 100km)
planetesimals due to heating, melting & differentiation - the outer layers of rock would insulate the iron-nickel core.
The stony meteorites can be classified into three types according to the degree to which they have been
heated (and altered):
1 Chondrites - containing chondrules (rounded bits of glassy rock not much larger than a pea, Fig. 19.2b), probably the first quickly solidified droplets of
matter which condensed out of the solar nebula (or drops of molten fragments from planetesimals collisions); they have been slightly heated to drive off
volatiles (carbon compounds and water).
2 Carbonaceous chondrites contain both chondrules and volatiles - therefore they represent the least altered remains of the solar nebula. Three types of
carbon grains (diamond, graphite & silicon carbide) recently discovered seem to be few million years older than the solar system (Sci. Am, Oct. 90, 14-5).
3 Achondrites - containing no chondrules and no volatiles - apparently most heated remains of the solar nebula (they are similar to the Earth’s lavas).
Internet:
http://bang.lanl.gov/solarsys/tercrate.html Terrestrial Impact Craters
ASTEROIDS (Minor Planets; 19.2, 458 - 461)
Total number estimated: several 100,000 stony bodies: maximum 1003km Ceres; 540km Pallas; 538km
Vesta (Astronomy Dec. 97, p. 30, 34); 240km Herculina (has a 50km satellite at about 975km); 53km
Achilles; 23km Eros; 16km Hidalgo; 243 Ida has a 1.5km baby Ida at 100km (Astronomy Jul 94, 18);
others are smaller than 1 km; more than 15,000 orbits are known (Dance of the Planets, 1995); 88% are
very dark (reflect 5% to 0.02% light) - correspond to carbonaceous chondrite meteorites; the other
major group (1%) is reddish and more reflective (10-20% albedo) correspond to stony-iron meteorites;
most are irregular in shape (such as the satellites of Mars: Phobos & Deimos, 412 ).
Nördlingen, “Ries Crater”
Possible FIELD TRIP
Meteor crater, 24 km diameter, 14.87 ±0.36 million years old (Miocene); impact of a lithic (stony) meteorite, diameter about 1 km, relative velocity of
more than 20 km/second, formed explosive energy of about 250,000 Hiroshima bombs. As a result, tektites, variety Moldavites in southern Bohemia
(about 400 km eastwards) are assumed to form by the impact.
Meeting: McDonalds, Heidelberg, Hebel Str. 4, 7:30h..
Nördlingen: from Heidelberg along A6 + A7, then B29; from Stuttgart along B29; meeting at the north city margin, parking
area “Kaiserwiese” 10:15h, then walking to the Rieskrater Museum, Eugene Schoemaker Platz 1 (phone 09081-273 8220;
director Dr. Michael Schieber), about 10:00 to 12:00h; lunch at Café Altreuter (at Daniel; Marktplatz 10; phone 09081-4319),
and 13:00 – 14:15h. “Kaiserwiese”. Return about 15:00 (latest 16:00h).
Near Earth Objects:
http://cfa-www.harvard.edu/iau/lists/Sizes.html
http://cfa-www.harvard.edu/iau/lists/Dangerous.html
http://cfa-www.harvard.edu/iau/lists/MPLists.html
their sizes
list of the dangerous ones
their list according to categories.
Van OORT CLOUD and COMETS (19.3, 459, 462 - 469)
A comet is a lump of “dirty” fluffy ices of water, carbon dioxide, etc. (the fluffy ices have a very low
density, 0.1 to 0.25 g/cm3: p. 410) only a dozen kilometers in diameter and orbiting on a very eccentric
ellipse around the Sun. Whenever it occurs within the inner solar system, the comet’s ices vaporize due
to the Sun radiation, dust is released and the molecules of the gas are broken into the atoms and ions we
see in the head (coma). The coma’s vast cloud of gas and dust may grow up to 100,000 km in diameter 7-times the diameter of the Earth (464). The gas in the coma is made up of water, carbon dioxide, carbon
monoxide, hydrogen, etc.. The tail springs from the coma and typically extends 10 to 100 million km
(max. 1 AU = 150 million km). More than 1,300 orbits of comets are known. The source of the comets
is assumed in the van Oort & Edgeworth - Kuiper belts (462-3, 446-7, 466).
Mysterious Sun grazers: comets plunge into the Sun - more common than once believed (Astronomy, 4/Apr 92, p. 46-49). Pieces of comet ShoemakerLevy 9 collided with Jupiter around July 21, 94. Over the course of several days, the comet fragments (there are at least 20) each came up from below
Jupiter and passed behind the planet as seen from Earth. As each piece plunged through the atmosphere, it exploded, creating a long-lived disturbance.
About 90 minutes after each collision, the impact site rotated into view (Jupiter rotates from left to right). The famous Italian astronomer Giovanni Cassini
recorded a hit on Jupiter: the spot evolved between December 5 and 23, 1690 (Astronomy May 97, p. 34+36).
The popular short-period comet Halley (period 76 years) has been observed ’85–‘86 by five spacecraft (462; its nucleus by Giotto,).
The comet of century, Hale-Bopp, had a perihelion on April 1, 97 (Astronomy, Mar ‘97, p. 56-61, 62-68, 69, 71). The maximum brightness was -1.8 mag.
http://www.ESO.org/comet-hale-bopp/;
http://www.halebopp/com
http://www.esa.int/science/giotto
Interstellar (“Rogue”) comets may appear (at a magnitude 22 - 25) one every few years, in the area of Hercules (Astronomy, Feb 97, p. 46-51). Relative
abundance of acetylene, hydrogen cyanide & isocyanate found on the comet Hyakutake indicate its interstellar origin (Astronomy May ’97, p. 36).
7 Sa, 4 Jan 06:
FIELD TRIP 1, to Pirmasens’ surroundings – geologic development of
the Earth;
take appropriate clothing & food.
Meeting: McDonalds,
10
Tu, 14 Feb 06, TEST 2
Ch. 16:
TOPICS
Survey of the solar system: 11 objects (incl. asteroids & van Oort cloud) orbiting around the Sun in autonomous orbits - their sequence in ascending order
from the Sun; rough distances from the Sun in AU (Mercury 0.4 AU, Venus 0.7 AU, Earth 1 AU, Mars 1.5 AU, Asteroids 3 AU, Jupiter 5 AU, Saturn 10
AU, Uranus 20 AU, Neptune 30 AU, Pluto 40 AU, van Oort cloud 2,000-20,000 AU)
361-375, Tab. 16.1
9 planets in a sequence of their decreasing size (expressed in the Earth’s diameters)
Appendix Tab. A-13, p. 503
3 basic common properties of the solar system (revolution in nearly the same plane, counter-clockwise when seen from north; age about 5 billion years);
exceptional orbit in inclination (Pluto, Mercury), eccentricity (Pluto, Mercury and Mars) and revolution direction (clockwise when seen from north: Triton,
Charon), rotational direction (clockwise when seen from north: Venus, Uranus, Pluto)
361-375, Tab. 16.2
2+1 planetary types - short description (terrestrial, Jovian; Pluto is extra)
362
3 types of bodies of the solar system in addition to the planets (space debris: asteroids, comets and meteoroids)
363-366
Solar nebula: event which triggered its origin (supernova explosion within 60 light years about 5 billion years ago; its chemical evolution (temperature
decreasing from its center controlled the condensation sequence)
16.1: 356-359
Ch. 17:
Evolution of terrestrial planets - 4 processes (stages), shortly describe each: differentiation, cratering, flooding by lava and/or water, slow surface evolution
382, Fig. 17-2
Geological activity of terrestrial planets - 3 types, shortly describe each: plate tectonics, volcanism, exogenic agents
382-387
Atmosphere on solar system bodies [except Jovian planets] (Venus, Earth, Mars, Titan, Triton), shortly describe each.
386-7, 397-402, 404-5, 433, 444-2
Ch 16, 17:
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Volcanism on solar system bodies (recent: steam + CO2 on Earth, (S?), CO2 + SO2, on Venus; S + SO2 on Io; water spraying on Europa and Enceladus;
liquid nitrogen eruptions on Triton; extinct: weak on Moon, strong on the Earth & Mars)
432, Fig. 18.11, 444, .
Tidal heating (explanation & importance; examples of the best evidence)
T.G. 3, 430-431
Terrestrial planets and many satellites of the solar system are not perfectly rigid. If they are subject to a changing gravity from neighbor bodies in direction
and/or strength, they deform, and this deformation constantly changes (=flexing). The flexing is resisted by friction, which causes heat.
The deformation change (driven by orbiting and spinning energies of the involved bodies), resisted by internal friction of the rocks, consumes a small
portion of the spinning and/or orbiting energies, which changes into heat, and the spinning and/or orbiting become slower. Tidal heating slows the bodies'
rotation until it becomes tidally locked to its orbiting period, the tidal bulge does not move (change) any more, and the heating stops.
The tidal heating can be remotely observed only if a resulting volcanism can be observed, which may form as follows: the tidally generated heat cumulates
in the subsurface material (the overlying material insulates from heat losses) and causes its melting, eventually degassing or partial vaporization. These
results are known on several solid bodies of the Solar system. Planetologists call them volcanism, even if the melting/vaporization takes place at a very low
temperature (such as that on Triton – at –210°C [=63 Kelvin]).
On the Earth, magmatic chambers are located shallow within the crust and are slowly rising due to convection currents in the magma. The hot magma
rises to the chamber’s ceiling; the ceiling rocks melt; the cooler magma sinks to the chamber’s bottom and crystallizes into igneous (magmatic) rocks. The
magma contains a great percentage of (volcanic) gases dissolved under high pressure. As a magmatic chamber rises, the pressure acting on the magma from
overlaying rocks decreases. When this environmental pressure becomes lower than the magmatic gas pressure, the compressed dissolved gases abruptly
separate from the solution in form of bubbles: an explosion takes place and forms a volcano.
Three (from many) examples:
1
The Moon. Moon’s rotation, originally faster than now (the Moon showed all sides), has been tidally locked to the Earth since 3.5 bill. y. ago (p. 70-1,
430), thus the Moon does not have any active volcanism since that time (the youngest volcanic rock and/or crater is 3.5 bill. y. old.
2
Io (the closest Galilean moon of Jupiter). The heat driving Io’s strong volcanism (strongest in the solar system) comes from tidal heating (p. 430). Io is
subject to constantly changing deformation (flexing). The other Galilean satellites Ganymede (the largest solar system satellite) and Europa cause
perturbations in Io’s orbit so that its distance from Jupiter varies slightly within the strong Jupiter’s gravity field. Though Io’s rotation (as that of the
other Galilean satellites) is tidally locked to Jupiter (such as the Earth’s moon keeps one side turned to the Earth), Jupiter’s gigantic gravitational field
is so strong that even slight Io’s orbital perturbations by Ganymede and Europa cause great tidal distortions of Io. This heating of Io’s interior is
sufficient for all the volcanic activity. In fact, Io’s neighbor satellites Ganymede and Europa:
flex Io at every conjunction with Io;
pull Io’s orbit into slightly elliptical (eccentric) one and thus the Jupiter’s changing gigantic gravity field flexes Io.
3
The Earth. The gravity fields of the Moon and the Sun draw up the near side rocky surface of the Earth rotating daily on its axis into bulges a few
inches high (p. 70). As the Earth rotates, these bulges, dragged by the Moon and/or Sun, move from east to west: they flex, and heat the Earth
materials by friction among the rock crystals. Because this friction is very strong, discontinuities, such as faults, preferably enable the motion at a
lower friction (slip), and leave the rocks largely undeformed; therefore the heating is concentrated onto these active faults, particularly oceanic plates
subject to subduction. This is why volcanic chains occur above a subducted plate (e. g.: Cascades, volcanoes in Chile, Alaska, etc.).
Pluto + its satellite Charon, each is tidally locked to other (Pluto’s day = Charon’s orbit period = Charon’s day = 6 days, 9 hours, and 18 minutes;
Astronomy, July 1986, page 17); therefore, the gravity pull of Charon does not change on Pluto, and there is no tidal heating on Pluto caused by Charon.
Of course, Pluto’s highly eccentric orbit (the strongest among the solar system planets), may cause some tidal heating on Pluto; however, such an effect has
not yet been observed due to very limited knowledge about Pluto (the only planet not visited by a man-made spacecraft).
SUN (7, 122-37)
Sunspots:
http://www.ncsa.uiuc.edu/Cyberia/Bima/flares.html
Eruptions:
http://kukui.ifa.hawaii.edu/
http://hesperia.gsfc.nasa.gov/sftheory/
http://www.spaceweather.com/
SOHO observation:
http://sohowww.nascom.nasa.gov
SOLARMAX observation:
http://guinan.gsfc.nasa.gov/docs/heasarc/missions/solarmax.html
1 THE SOLAR ATMOSPHERE (7.1, 124-9, Fig. 7.1, 124)
a PHOTOSPHERE = the visible surface, most of the light source: thin layer (500km thick)
Temperature 5800 - 6000 Kelvin (124, 126). Below the photosphere: the gas is denser & hotter - it
radiates more light but it is hidden by the photosphere. Photosphere’s density is about 0.1% that of the
Earth’s air at sea level (100% of the air’s density is about 70,000 km below the photosphere).
Photosphere provides an absorption spectrum (the continuous spectrum of the deeper photosphere is
filtered by the upper low density gases). Granulation is due to rising and sinking gas of convection cells
(Fig 7-2, 126) just below the photosphere; the bright cells have the diameter 1500 km, each lasts about
10 minutes).
b CHROMOSPHERE - (Greek chroma = color) - nearly invisible layer about 10,000 km thick
It is about 1000-times fainter than the photosphere; it is visible as a thin line of pink only during the
solar eclipse when the photosphere is covered by the Moon: it provides brilliant emission spectrum - red,
blue + violet Balmer lines of hydrogen (and few lines of other elements) indicate that the chromosphere
is much hotter and much less dense than the photosphere. The chromosphere projects by spicules
(flame-like structure) into the lowest corona: the spicules have diameter 100 - 1000 km, up to 10,000 km
high, last 5 - 15 minutes; relatively cool regions (about 10,000 Kelvin) extending into much hotter
corona (500,000 Kelvin). The spicules spring up around the edges of super-granules - Fig. 7.4b, 126-7.
c CORONA - outer atmosphere extending beyond the planets
Due to very high temperature (1,000,000 Kelvin), the high velocity of particles smears out any
absorption line - a continuous spectrum forms due to the Doppler’s shift. Lower (or K) corona: 500,000
to 1,000,000 Kelvin, outer (or F) corona: 2,000,000 Kelvin, 1 - 10 atoms/cm3. The outer corona is so
hot the Sun is unable to hold it - the flow of protons, electrons and ions of heavier elements at 300 - 800
[1000] km/sec = solar wind. The outer corona extends beyond the planets.
2 SOLAR ACTIVITY (7.2, 129-35)
a SUNSPOTS - dark (cool: about 4240 Kelvin, orange-red glow) areas of the photosphere
Single spots may last for a week, but mostly in groups up to 100 spots, which may last up to two
months; mean spot is about twice the Earth’s diameter. Caused by about 1000-times concentrated
magnetic field (Zeeman’s effect doubles single spectral lines), which inhibits gas motion just below the
photosphere, and rising currents cannot deliver their heat to the surface. However, according to the latest
research (Richard Wilson & Hugh Hudson [University of California at San Diego], see Nature, 28
April 1988, and Astronomy, October 1988, p. 22-31), more sunspots seem to mean a brighter Sun;
apparently, during the sunspots occurrence, more energy comes up from deep within the Sun that
appears in regions rather far removed from those of the spots, increasing the total Sun’s luminosity by
about 0.1%. There is no explanation of this observation yet. The number of sunspots varies with a period
of about 11 years - the sunspot cycle. At the beginning, the spots start to appear in the middle
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latitudes symmetrically 30°-35° north and south of the solar equator, and progressively approach the
equator within 5°-7° - the Maunder butterfly diagram (130, Fig. on the bottom); E. Walter Maunder
noticed that very few sunspots appeared 1645-1715 = Maunder Minimum which can be linked to the
“little ice age” (1430-1850).
b The MAGNETIC CYCLE includes a magnetic reversion of the sunspots.
Therefore, the magnetic cycle takes 22 years - double of the sunspot cycle. The magnetic reversals are
probably due to the Sun’s differential rotation: faster at the equator (25 days) than at a middle latitude,
45º (27.8 days). The winding of the magnetic field to explain the reversals has been suggested by
Babcock (133-4, Fig. 7-10). On 25-Feb-01, the magnetic cycle reached its maximum and flopped:
http://science.msfc.nasa.gov/headlines/y2001/ast15feb_1.htm .
c CHROMOSPHERIC & CORONAL ACTIVITY (134-5).
PROMINENCES (36-7, Fig. 3-7B, 134, 136) are clouds of ionized gas in the Sun’s upper
chromosphere/inner corona, with a higher density and at a lower temperature than their surroundings.
They are visible as bright red projections beyond the limb. When viewed against the brighter disc they
appear as dark absorption features and are termed filaments. Prominences are trapped in the twisted
magnetic fields of active regions. They exhibit a great diversity of structure and are most conveniently
classified according to their behavior, as either quiescent or active. Quiescent p.-s are particularly longlived and are among the most stable of all solar features. They may persist for several months before
breaking up or, less frequently, blowing up and have been known to reform at the same location with an
almost identical configuration. Typically, they are a couple of 100,000 km long, several 10,000 km high
and several 1000 km thick. They occur in high latitudes, where they are supported by the horizontal
magnetic field separating the polar field from the adjacent fields of opposite polarity. They attain their
greatest frequency a few years after the minimum of the sunspot cycle, when their average latitude is
around ±50°. Then they appear in increasingly high latitudes, reaching the polar regions shortly after
sunspot maximum. Then, after a brief discontinuity, they reappear around latitude ±50° and remain there
in small numbers until a few years after the next minimum, when they again progress poleward. Active
(eruptive) p.-s are relatively short-lived and may alter their structure appreciably over a matter of
minutes. There are many characteristic types, e.g. surges & sprays, in which chromospheric material is
ejected into the corona, loop prominences and coronal rain. Loop prominences are impulsive events that
often accompany flares, while coronal rain represents the return of flare-ejected material. In developing
active regions arch filaments are usually present. These tend to connect regions of opposite polarity
across the line of inversion and gradually ascend while material descends along both sides of the arch.
FLARES are much more violent (137): sudden short-lived (a typical flare attains its maximum in a few
minutes and then slowly fades in an hour or less) eruptions of the upper chromosphere/inner corona that
are optically visible as brightening of small areas (usually of less than several 100,000,000 km2) usually
only in the monochromatic light of certain strong Fraunhofer lines. They represent an explosive release
of energy (up to 1025 joules = 2 billion megatons of TNT, the temperature in a flare can reach 500,000 K;
X-ray observations suggest that some nuclear reactions occur in flares) - in the form of particles &
radiation - that cause a temporary heating of the surrounding medium and may accelerate electrons,
protons and heavier ions to high velocities (up to 1000 km/sec). Flares are controlled by the Sun’s
magnetic field: they occur when sharp twists in the magnetic field store up great energy quantities and
then release it at once. They usually occur near sunspot groups (a large spot group may experience 100
flares a day). Flares can have important effects on Earth. Together with a flare’s visibility (8 minutes
after its flashing on the Sun), a strong X-ray and ultraviolet radiation reaches the Earth. It increases
the ionization in Earth’s upper atmosphere in the daylight hemisphere. The ultraviolet radiation causes
fade-out of short-wavelength radio signals due to strengthening (by increased ionization) of the
reflectivity of the D layer of the ionosphere (60-90 km altitude), which suppresses the passage of the
signals to the higher layers where they are normally reflected. This is accompanied by a sudden increase
in the electrical conductivity of the E layer (90-140 km altitude) and by disturbances of the Earth’s
magnetic field. Occasionally, within about half an hour of the flare, low-energy cosmic rays reach the
Earth, and within about 26 hours, on average, less energetic particles of the solar wind may arrive.
These latter particles spiral around the Earth’s magnetic field lines, causing geomagnetic storms and
their luminous counterpart, auroras (glow of excited atoms at altitudes of 100-400 km). Other effects:
surges in high-voltage power lines, radiation hazards to passengers in supersonic transports and in
spacecraft.
The coronal activity is controlled by the strength & configuration of the magnetic fields.
The overall shape of the solar corona changes with the phase of the sunspot cycle. Streamers of the
corona extend to a few solar radii, where they are returned back by magnetic loops. Coronal holes of
very low density gas form where the particles stream away unimpeded (the source of the solar wind).
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The PROPERTIES of STARS
8, 146 - 167
A determination of the intrinsic properties of stars (energy emission, diameter, mass and density)
depends on the distance to stars (for galaxies, see distance indicators, 287).
Measuring the DISTANCE to Stars (146-155)
a Parallax is the angle between two observation directions of an object. The distance to the object can
be calculated from the exactly known distance between the two observational positions (baseline, it
should be perpendicular at its center to the object’s direction) and from the measured parallax. The
longer the distance the longer the baseline should be. Our distances to stars are enormously long; the
shortest of them can be measured by the annual parallax method using the baseline which equals 2 AU
(diameter of the Earth’s orbit); the parallax is measured as a star’s shift against the sky background from
opposite sides of the Earth’s orbit (at six-monthly interval). Using the trigonometric principle, the
distance = ½baseline×cotangents of the parallax (this is why the stellar parallax p uses the half the star’s
shift). Because of the very small angle of a parallax, the trigonometric relationship can be simplified
into the small angle formula (Reasoning with Numbers 3-1, 35, 8-1, 148; Fig. 8.3, 147):
d[AU] = 206,265/parallax[seconds of arc] .
Because the parallax of even the nearest stars is less than 1 second of arc, the distance in AU is inconveniently larger than the constant 206,265 AU. To keep the numbers manageable, the distance is expressed
in the 206,265-multiples of the AU = parsecs (1 parsec = 206,265 AU = 3.26 light years, TG-p. 1):
d[parsec] = 1/parallax[seconds of arc] .
Therefore, a parsec is the distance to a star whose parallax is one second of arc. If the parallax can be
measured then so can the distance. 'Parallax' is thus often used synonymously with 'distance'.
b Spectroscopic parallax (154-5, Reasoning w. numbers 8-3, 151) is the distance calculated from the
difference between the apparent and absolute (intrinsic) magnitude (m-Mv). This difference is known
as a distance modulus (Reasoning w. numbers 8-2, 150). The absolute magnitude equals the apparent
magnitude the star would have if it were at a standard distance of 10 parsec away.
The absolute magnitude of a main-sequence star is deduced from its spectral type using the Hertzsprung-Russell diagram (Fig. 8-6, 152). This method is
applicable for more distant stars which do not have their annual parallax measurable, reveal a clear spectrum and belong to the main-sequence stars. See
later.
The value of the distance modulus is proportional to the star’s distance:
m-Mv = 5 log10(distance[parsec]) - 5 ;
From this formula, the distance in parsec can be calculated as follows:
log10(distance[parsec]) = (m-Mv)/5 + 1 .
distance[parsec] = antilog10(distance[parsec]) = 10(m-Mv)/5 + 1
EXAMPLE (Reasoning w. numbers 8-2, 150): Deneb has absolute magnitude -7.19 (1.26-8.45); Sun’s apparent magnitude = -26.7 (Reasoning w. numbers
2-1, 17), Sun’s absolute magnitude is 4.78; how distant Deneb would have to be to have the Sun’s apparent magnitude? In other words: at which distance
would Deneb shine as the Sun?
SOLUTION:
substitute -26.7 for m (the required apparent magnitude),
substitute -7.19 for Mv (the absolute magnitude of Deneb) and the result is:
log10d = (-26.7+7.19)/5 +1 = -2.902
d = 0.0012531412 parsec = 258.479 AU = 38 667 932 440 km
In words:
Deneb is so bright, that it would replace the radiation of our Sun at a 258.5-times longer distance.
c
d
16
Period - luminosity relationship using -Cephei variable stars (TG-p. 20);
Hubble’s law (290, Reasoning w. numbers 13-1), using red shift, due to the universe’s Big-Bang
expansion; for distances >6000Mpc (Doppler’s effect, Reasoning w. numbers 6.2, p. 117; relativistic
red shift/Doppler formula, 315-7.
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DIAMETERS of STARS
HERTZSPRUNG-RUSSELL DIAGRAM (8.6 152) relates the intrinsic (absolute) brightness (magnitude
or luminosity) [vertical axis] of stars to their surface temperature (spectral type, color) [horizontal axis].
It enables to sort the stars according to their diameters, since it separates the effects of surface
temperature and surface area on stellar luminosity. In 90% of stars, their surface temperature changes
proportionally with their intrinsic luminosity and vice versa; these stars appear in the H-R diagram as a
diagonal band known as the main sequence stars. In the area of a higher luminosity (due to a greater
surface area) and lower temperature, giants & super-giants appear, whereas in the area of a lower
luminosity and a higher temperature white dwarfs appear. The main sequence stars start their lives
fusing hydrogen fuel on the lower left edge of the diagonal band known as the zero age main sequence
(ZAMS, 192, Fig. 9.16; see life expectancy, TG-p. 18). A gradual increase of luminosity and temperature
decrease move the star’s plot upward and to the right, reaching the upper right edge of the main sequence
band: they have exhausted nearly all hydrogen in their centers, evolve rapidly and die.
From the H-R diagram - the diameter of a star is proportional to the square root of luminosity (because
the luminosity is proportional to area).
Luminosity classes - (153, 155, Fig. 8.10, 162-3) from the spectral lines width: proportional to the size;
on the Fig. 8.8, 154, constant radius is shown by diagonal lines.
MASSES of STARS
From the binary stars - measuring their orbital period & size of each orbit (Fig. 8.11, p. 156; By the
number 8-4, 157):
Visual binaries (Sirius, 158, Fig. 8.12) - limited to the nearest stars;
Spectroscopic binaries (Capella, Alcor, Mizar, 158-160, Fig. 8-13, 8-15) - Doppler shift & orbital
period give orbit’s circumference. Limited by the unknown orbital tilt: therefore the results present
minimum values. Not applicable for too small stars with no spectrum.
Eclipsing binaries - from a light curve (159-161, Fig. 8-17); often even the spectra are available and
thus the velocities, often the diameters are directly measurable from the light curve period and velocity
(Algol [ Persei], 160).
From the luminosity of the main sequence stars (giants, super-giants & white dwarfs do not follow this
rule, 162-4, Reasoning w. numbers 8.5; see also 193, Reasoning w. numbers 9-1):
L = M3.5
M = L1/3.5
DENSITIES of STARS
3 major groups of densities reflecting different stages in the stars' evolution can be distinguished (162-3):
1 Main sequence stars - density is about 1 g/cm3 ,
2 a
giant stars - density is about 0.1 - 0.01 g/cm3 ,
b
big super-giants -density is about 0.001 - 0.000 001 g/cm3 (their centers are, however, very
dense: 3,000,000 g/cm3),
3 White dwarfs (about 1-mass, size of the Earth) - density of about 10,000,000 g/cm3 .
STARS and their EVOLUTION
11 Th, 16 Feb 06
9 - 11, 179-196, 202-223, 230-247
The BIRTH of Stars
The source = interstellar medium (174) = large cool clouds of gas (75% H, 25% He + traces of carbon,
nitrogen, oxygen, calcium, sodium, and heavier atoms) + 1 - 2% fine dust (carbon, iron and silicates). It
is recognizable by interstellar reddening and by absorption lines of cool gas. The interstellar medium
shows extremely low density expressed by very few atoms/volume:
cool (10 - 50 K) “dense” clouds
- 10 to 1000 atoms/cm3, are pushed & twisted by currents of the
hot low density gas
- 0.1
atoms/cm3.
Therefore, the interstellar medium is not dense enough to collapse and form stars by gravity
spontaneously. The cloud contraction is counteracted (178-9) by a thermal diffusion of the gas (even 10
K hydrogen moves about 0.5 km/sec) and turbulence. A triggering by a shock wave from a supernova
explosion [Fig. 9.5, 179] (or from galactic spiral arms) is needed to cause collisions: they concentrate
clouds and fragment them into clusters of 10 to 1000 stars which wander away and the cluster
disappears within few 100 millions of years; beforehand: proto-stars as cocooned red giants (cocoon of
dust & gas - infrared source) form due to gravity (originally free fall, later slowed by an increasing
density and internal pressure) compaction which results into heating and hydrogen fusion phase which
can stop the contraction - stage of -Tauri-stars (cocoon stars clearing the surrounding nebula) and
Herbig-Haro objects (shreds of cocoons, 185).
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Lower mass star cannot become very hot: proton - proton chain (138-141). A massive star becomes hot
enough to ignite the CNO cycle (183, 186). The mass controls the temperature and thus the fusion type:
solar masses temperature (million Kelvin) fusion type
fusion product
<1.1M
10 - 16
proton-proton
helium
>1.1M
16 – 100
He chain, CNO-cycle
helium, carbon as catalyst
100 – 600
helium fusion (triple alpha)
beryllium + carbon
600 - ?
carbon fusion (supernova)
Si, N, O, F, Ne, Na, Mg, Al
still higher
Mg + Si
heavier elements
Pressure-temperature thermostat (186) regulates the reactions in the core. A high internal temperature
rises pressure which makes the star expand; the gas expansion cools the star, slowing its nuclear reaction
& making it compact - speeding the nuclear reaction & increasing the internal temperature. The more
massive, the more weight the star must support, the higher the inner pressure & temperature; thus the
mass determines the luminosity.
The star models are based on 4 laws (187-91): 1+2 Mass & Energy conservation, 3 hydrostatic
equilibrium (the layer weight is balanced by internal pressure), 4 Energy flow outwards in proportion to
the temperature gradient (3 types of the heat transfer, 188, Fig. 9-12) according to the matter density: by
conduction in the most dense material - in white dwarfs only, by convection in the medium density least
massive stars (<0.4 -masses: red dwarfs [makes burning efficient due to mixing]), and by radiation in
the least dense medium such as the big envelopes of very massive stars (more than 3 -masses).
AGING (191-196) & the DEATHS of stars (10, 200-223)
The core contracts by gravity, its temperature increases, releases more energy = luminosity increases;
outer layers expand and cool: - the star grows larger, brighter, and cooler, i.e. it moves upwards right
from the zero age main sequence line (ZAMS, from the base line, Fig. 9-16, 192-3).
The life expectancy: Because the fuel consumption rate is proportional to the luminosity L (Reasoning
w. numbers 9-1, 193), the life expectancy T = fuel/rate of consumption = M/L = M/M3.5 = 1/M2.5. If the
Sun has about 10 billions years of total life then a star with 4 -masses has T = 1/42.5×10 billion y. =
1/32×10 billion years = 310 million years.
'When a star’s central hydrogen fusion ceases, its core contracts and heats up, igniting a hydrogen-fusing
shell and swelling the star into a cool giant. The contraction of the star’s core ignites helium first in the
core and later in a shell; if the star is massive enough, it can eventually fuse carbon and heavier elements'
(201 - 214).
MASS categories (186, Fig. 10-6):
_-masses (M. stands for mass, PTT for pressure-temperature thermostat)
<0.08
brown dwarfs:
no fusion; they glow faintly for 100 my, then cool & dim;
<0.4
red dwarfs (214):
due to complete convective mixing no H-shell fusion, no He-core die as white dwarfs;
0.4 - 3.
medium-M. stars (Sun): partially convectively mixed - H-core fusion ignites H-shell a giant forms: He-core fuses -”planetary nebula” around a white dwarf
if <1.4
white dwarfs (217-9)
(after billion of y.) cool into
black dwarfs
3.0 - 9.
as the medium-M. stars but the carbon-oxygen core becomes degenerate: PTT=off, heating to
600 mill.K causes carbon detonation of SUPERNOVA, neutron star or black hole form;
>9
before it degenerates, carbon fuses (no detonation) controlled by PTT
iron core forms & collapses: supernova
Compact objects = end states of the stellar evolution due to mass collapse:
<1.4*
white dwarf - degenerate matter, about the size of the Earth, no nuclear reaction;
>1.4
neutron star, 20 km diameter, degenerate neutrons (230-8);
>3
black hole (240-2).


18
Chandrasekhar limit: no white dwarf can have a mass greater than 1.4-masses; a greater object will change into a neutron star (211-23, Fig. 10-17).
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THE MILKY WAY
12, 252-276
The Milky Way is one of the largest star systems = galaxies: more than 100 000 l. y. diameter, more
than 100 billion stars.
Almost every celestial object visible to naked eye is part of the Milky Way galaxy. Exceptions:
Magellanic clouds - small irregular galaxies in the southern sky - appears to be satellites of our galaxy;
Andromeda galaxy (similar to the Milky Way galaxy) - the largest galaxy.
Only 10% of the Milky Way is in the visible wavelength: the majority is behind dust clouds - within an
infrared and microwave visibility.
Determination of the Milky Way galaxy’s SIZE (Harlow Shapley):
1 Variable stars - a dying star after it leaves the main sequence, it changes into a giant and moves
back and forth in the giant region of the H-R diagram; passing the instability strip (Fig. 12.3, 256-8), it
can become unstable - expand/contract within a period of a few hours to hundreds of years.
Two types are important:
RR Lyrae stars, 12 - 24h period, absolute. magnitude about +0.5;
Cepheid stars (-Cephei), 1 - 60 day period, various absolute magnitudes; the period is proportional to
luminosity and enables to determine the absolute magnitude and from it the distance.
2 Globular clusters - very old (10 - 15 by.); Shapley determined their distance by their Cepheid
luminosity - period relationship. Since the distribution of globular clusters must be dominated by
gravity, Shapley realized that their center must show the galaxy’s center revealing the correct size of the
Milky Way (Fig. 12-7, 260, Fig. 12-11, 262).
TWO COMPONENTS of the Milky Way galaxy the differences between them illuminate our galaxy’s past
1 Disk component includes: “Population I stars” - they are: young, metal-rich (2-3% elements
heavier than helium), in nearly circular orbits; associations & open star clusters, and nearly all of the gas
& dust.
2 Spherical component includes: halo - a thin scattering of randomly elliptically orbiting “Population
II stars” - old, metal-poor (0.1% elements heavier than helium), cool (lower main sequence & giants,
but almost no gas & dust) with globular clusters and the nuclear bulge (similar stars & young hot stars
[observable at radio, infrared + X-ray]); an extended halo known as galactic corona is now assumed to
extend up to seven times farther than traditional estimates due to some dark matter (massive neutrinos or
similar exotic particles?).
ROTATION of the Milky Way galaxy required for balancing the gravity (mass)
The disk stars have nearly circular orbits in the galaxy plane. E.g., Sun is a disk star, moves about 220
km/s toward Cygnus, orbit radius is 8.5 (7-10) kpc, period is 240 my.; therefore, the mass of the Milky
Way galaxy would be about 140 billion -masses. BUT:
The rotation of the disk is differential (not rigid), and non-Keplerian (Fig. 12.12, p. 263) - stars farther
from the center move faster because their orbits enclose many times more unknown mass. Motion in the
halo: each star + globular cluster follows its own randomly tipped elliptical orbit (slow outside, fast
inside the galaxy).
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STELLAR POPULATIONS of the Milky Way galaxy
(Table 12.1, 264, Fig. 12.14, 266)
Two stellar populations referring to the two galaxy’s components can be distinguished, each with a
gradation “extreme” and “intermediate”. Accordingly, metals content, location and orbit shape show a
change consistent with the stellar age, i.e. with our current explanation of the Milky Way Galaxy
formation (see the next paragraph).
POPULATION II
POPULATION I
Extreme
Intermediate
Intermediate
Extreme
Location:
halo
nuclear bulge
disk
spiral arms
examples: globular clusters
Sun
stars in Orion
Orbit shape:
highly elliptical
moderately
slightly elliptical
circular
elliptical
Metals:
< 0.8%
0.8%
1.6%
3%
Age in bill.
oldest
medium
young to medium
youngest
years:
10-14 by.
2-10 by.
.2-10 by.
<0.1 by
The FORMATION of the Milky Way galaxy
(Fig. 12.15, 267-268)
The Milky Way galaxy originated as a swirl of hydrogen and helium gas that lead to formation of
clusters of metal-poor stars with spherical distribution of random orbits that we see today as the
halo. However, many of the clusters contained too few stars to hold themselves together: they gradually
dissociated, freeing stars that wandered through the spherical cloud. Only clusters with more stars
packed in a smaller volume survived and have developed (during over 10 billion years) into the highly
stable globular clusters.
Randomly moving eddies in the cloud collided with each other and canceled out: only parallel orbits
around a common axis persisted but could not resist the pull from the center of gravity of the sphere - the
sphere collapsed into a rotating disk which took billions of years. The halo population stars were left
behind as a fossil of the early galaxy; subsequent star generations formed in flatter distributions (the
intermediate population I stars are scattered hundreds of light-years above and below the plane of the
disk, the newest stars, the extreme population I stars, are confined to a disk only 300 ly thick).
As the galaxy flattened, the random elliptical orbits canceled out and more circular orbits remained.
Also, the metal abundance in the stars grew with every generation.
SPIRAL ARMS
(12.3, 268-272)
The spiral arms wind outward through the disk. They contain swarms of hot blue (O + B) stars, clouds of
dust & gas, and young star clusters. The O + B stars form three band (segments) near the Sun - farther
they are obscured by clouds. The spiral arms can be mapped by spiral tracers (all are young objects
therefore could not move): O + B star associations, young open clusters, clouds of hydrogen ionized by
hot stars (“emission nebulae”) and certain kinds of variable stars. Because the spiral arms are very young
they had to form the stars within them.
Radio maps (269-270; e.g., 21cm wavelength of cool hydrogen) disclose the spiral arms obscured at
visual wavelengths, particularly when unscrambled by measuring the Doppler shifts: a) the spiral pattern
we see near the Sun continues throughout the disk; b) the spiral arms are rather irregular and interrupted
by bends, spurs and gaps (e.g., the Orion stars appear to be a detached segment of a spiral arm); c) spiral
arms are regions of high gas density, contain young objects - active star formation suspected.
The density wave theory (270-2): the spiral arms are waves of compression rather like sound waves
which move slowly around the galaxy: the orbiting gas clouds overtake the spiral arms from behind and
smash into a density wave (Fig. 12-19, 271). The compression triggers the star formation; the massive
stars are so short-lived that they die before they can leave the spiral arm. If that star formation created
additional massive stars the process could be self-sustaining (272) and explain the complicated spiral
disturbances. The less massive stars emerge from the front of the arm with the remains of the gas cloud.
Two problems of the density wave theory:
1 How does the complicated spiral disturbance form? A density wave may form in response to:
a) minor fluctuations of the galaxy’s disk (a resonance principle);
b) collisions of galaxies.
However, the density wave, once established, will last for a billion years before it dissipates.
2 Formation of spurs & branches: only two-armed “grand design” galaxies can be explained, but
other galaxies are flocculent (“woolly”) [the Milky Way is intermediate: it contains both spiral arms and
flocculation] - these irregularities can be explained by the compressional triggering of star formation
which is self-sustaining. Some galaxies may be dominated by density waves due to interaction with
other galaxies  beautiful two-armed spiral galaxies, other galaxies may be dominated by selfsustaining star formation  flocculent galaxies.
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The NUCLEUS
(12.4, 273-276)
The nucleus is hidden by clouds of gas & dust in visual light but is “visible” on radio, infrared, X-ray
and gamma-ray wavelength: stars crowded together, a disk of gas spinning at the center, and clouds of
gas rushing outward.
Near Sagittarius - collection of radiosources, the most powerful, Sagittarius A, is the galactic core (2736). Expanding now (Doppler shifts at 21cm wavelength) - much of the neutral hydrogen is in a disk
hundreds of parsecs in diameter that is rotating and expanding outward.
Examples:
3 kpc arm (distance from center) = cloud of 107 M of hydrogen moves outward at 53 km/sec;
135 km/sec arm - expands away from us on the far-side of the nucleus.
Both may be parts of an expanding ring of matter expelled from the center about 100 my. ago. A ring of
much denser molecular (CO) gas clouds is 250 parsec from the center and expands outward at 140
km/sec.
The core center has 10 AU (0.000 05 pc) diameter, 5x106 M; it contains over a million cool stars,
violently moving hot low-density gas releasing a synchrotron radiation. Infrared observations reveal
tremendously crowded cool stars in the central parsecs of the Milky Way (268); wavelengths shorter
than 2 000 nm show that the stars are only 1 000 AU apart (in the Sun’s region: 330,000 AU = 1.6 pc).
Infrared longer than 4 000 nm reveals interstellar dust warmed by stars. Also X-rays and gamma-rays
(tremendously energetic - many have a wavelength of 0.0024 nm produced by the electron + positron
annihilation of matter into energy) indicate a giant energy source.
The energy machine (268-269) - probably a black hole containing at least 2.6x106 M at the center, a
giant version of the X-ray binaries discussed at the end of Chapter 11.2 (240-248); an accretion disk may
explain the 50 pc long hot gas filaments as if constrained by a huge magnetic field (273-6, at 20-cm
wavelength).
13 Th, 2 Mar 06
GALAXIES
13, 280-300
Galaxy types (Fig. 13.2, p. 282): elliptical (E), spiral (S), barred spiral (SB), and irregular (Irr).
Distance of galaxies (Fig. 13.10, p. 286-7) by Cepheid method (286, 157), and Hubble’s law (289-90,
Box 13.1, p. 290). The Hubble’s constant and the age of the Universe (Box 15.3, p. 335).
Diameter, luminosity & mass of galaxies (289-92).
Origin, evolution & distribution of galaxies (292-301); clusters of galaxies, colliding galaxies;
distribution of galaxies (Fig. 13.22, 13.23).
GALAXIES with Active Nuclei
14, 304-320
Exploding galaxies: active core galaxies; double-lobed radio galaxies, active galaxy nucleus (AGN,
306), Seyfert galaxies (306-9).
Quasars - distant or local (315-320)? Gravitational lens (293-4, 318-9, Fig. 14.10); relativistic red shift
(317) corrects (partially) the Doppler’s effect (Reasoning w. numbers 6-4, 128-9) for very high radial
velocities.
14 Sa, 4 Mar 06: FIELD TRIP 2, to Heidelberg, meeting at 69115 Heidelberg, McDonalds, Hebel Str. 4, 9:30h
http://teaching.grano.de/s_n_astr.htm
http://mail.map24.com/field_trip_hd
Max-Planck-Institute for Planetology, Gentner Laboratory &
Astronomical Observatory (LandesSternWarte),
15 Tu, Error! Reference source not found. Mar 06
COSMOLOGY (optional)
15, 324-350
The structure (geometry) of the universe; night sky is dark because the light from stars more distant
than the age of the universe permits: that light has not yet reached us, i.e., the universe is not infinitely
old, only 10 - 20 b.y. (Olbers’ “paradoxon”, solution by Edgar Allan Poe, 1848; p. 326-328, Fig. 15-1).
Cosmological principle: homogeneity & isotropy. Expansion; space × time geometry.
The Big Bang. Hubble’s law - uniform expansion, no center (289-290, Reasoning w. numbers 15-1,
330). The primordial background radiation is a black body radiation (Reasoning w. numbers 6-1, p.
107-9) with a temperature of 2.725 K; it lies in the infrared & microwave parts of the spectrum (Fig. 157, p. 331-333). The curvature of space (339, 346). The end of the Universe - critical density (337-341).
Grand Unified Theories (GUTs: 343-4).
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Test 3 TOPICS
Review for the FINAL EXAM:
TG –p. means Textbook Guide page
SPECTRAL ANALYSIS: 3 obtainable results (in addition to temperature: chemical composition,
radial velocity by Doppler’s principle, magnetic field of the radiation source by Zeeman’s effect;
http://userwww.sfsu.edu/rsauzier/Zeeman.html), and applications for planets, stars & galaxies.
[TG-p. 4-5, 14, 16-17]
ATOM’s STRUCTURE: its description and change due to a mass collapse of a star.
[TG-p. 4, 18]
MAGNITUDE & BRIGHTNESS: mutual relationship, applications for stars & galaxies. [TG-p. 1, 16-19]
SUN: its atmosphere, types of the solar activity.
[TG-p. 14-15]
DISTANCE of celestial objects: 4 methods of measurement applicable to various distances and objects
(angular or stellar parallax, spectroscopic parallax, period - luminosity relationship of Cepheid stars,
Hubble’s law - red shift due to universe expansion).
[TG-p. 16, 19)
MASS of celestial objects: methods of measurement & estimation applicable to various objects and
distances (binary star systems: visual binaries, spectroscopic binaries & eclipsing binaries; massluminosity relation of the main sequence stars: luminosity = mass3.5).
[TG-p. 17]
HERTZSPRUNG-RUSSELL (H-R) DIAGRAM: description & use (incl. evolutionary track). [TG-p. 17]
STELLAR DENSITIES - 3 groups.
[TG-p. 17]
STAR FORMATION: source from which the stars form, its composition & changes; triggering cause
of the changes.
[TG-p. 17 - 18]
PRESSURE - TEMPERATURE THERMOSTAT: description.
[TG-p. 18]
3 types of HEAT TRANSFER TYPES: when & where (in which objects) dominates each.
[TG-p. 18]
3 END STAGES of STELLAR EVOLUTION: massive objects (white dwarfs, neutron stars, black
holes) - mass conditions under which each takes place.
[TG-p. 18]
MILKY WAY: How the center & size of the Milky Way could be determined? Which type of rotation
of the Milky Way was determined, and what does it indicate? 2 galaxy’s components.
[TG-p. 19 (20-21)]
16 Error! Reference source not found., Error! Reference source not found. Mar 06FINAL EXAM: Sun’s at
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