Download PSCI1030-CHAP016-The Solar System

4/26/2010
Introduction
• Astronomy – the scientific study of the
universe beyond Earth’s atmosphere
• Universe – everything, all energy, matter, and
space
• Milky Way Galaxy – one of 50 billion galaxies
scattered throughout the universe
• Solar System – contains our sun and 9
planets
• Sun – supplies the energy for nearly all life on
the planet earth
Chapter 16: The Solar System
Homework: All questions on the
“Multiple-Choice” and the odd-numbered
questions on “Exercises” sections at the
end of the chapter.
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16 | 1
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Electromagnetic Spectrum
Intro
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Astronomy
Astronomers are interested in studying the full range of
electromagnetic spectrum coming from space
• But, much of the incoming solar radiation
does not make it to the earth’s surface – due
to atmospheric absorption
• Electromagnetic radiation that will pass
through the earth’s atmosphere can be
studied using ground-based detectors
• Other regions of the electromagnetic
spectrum must be detected by space-based
instruments
– The Hubble Space Telescope is a good example
of an instrument outside Earth’s atmosphere
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Intro
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Telescopes at the top of Mauna Kea, Hawaii
Intro
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Astronomy - Relevance
• Ancient Cultures – made numerous solar,
lunar, and celestial observations
–
–
–
–
365-day year – solar cycle
29.5-day month – lunar cycle
Calendars – agricultural & religious
One of the Mayan calendars had 18 months of 20
days & 1 month of 5 days (365 days total)
• Modern Cultures – celestial cycles still
relevant
– celebrate birthdays annually,
– academic years, seasons, monthly bills
Photo Source: Bobby H. Bammel
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Intro
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Intro
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The Solar System
The Solar System
• The solar system - complex system of
moving masses held together by
gravitational forces
• Sun is center
• Sun is the dominant mass
• Revolving around the sun -- 9 planets,
over 70 moons, 1000’s of other objects
(asteroids, comets, meteoroids, etc.)
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Section 16.1
• Geocentric Model – early belief that the
earth was motionless and everything
revolved around it
– Claudius Ptolemy (A.D. 140)
• Heliocentric Model – a sun-centered
model
– Nicolaus Copernicus (1473-1543)
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Johannes Kepler (1571-1630)
Section 16.1
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Drawing an Ellipse
• An ellipse has two foci, a major axis, and a
semimajor axis
• German mathematician and astronomer
• Kepler’s 1st Law – Law of Elliptical
Paths – All planets move in elliptical
paths around the sun with the sun as
one focus of the ellipse
• An ellipse is a figure that is symmetric
about two unequal axes
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Section 16.1
• In discussing the
Earth’s elliptical orbit,
the semimajor axis is
the average distance
between the earth
and the sun
Astronomical Unit
(AU) = 1.5 x 108 km
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Kepler’s Second Law
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Section 16.1
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The speed of a revolving planet varies
• Law of Equal areas – An imaginary line
(radial vector) joining a planet to the sun
sweeps out equal areas in equal periods of
time
• Perihelion – the closest point in a planet’s
orbit around the sun, speed is the fastest
– Perihelion occurs for Earth about January 4
• Aphelion – the
farthest point in a
planet’s orbit
around the sun,
speed is the
slowest
– Aphelion occurs for
Earth about July 5
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Section 16.1
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Section 16.1
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Calculating the Period of a Planet Example
Kepler’s Third Law
• Calculate the period of a planet whose
orbit has a semimajor axis of 1.52 AU
• T2 = k R3
1y2
• T2 = AU3 x (1.52 AU)3
• T2 = 3.51y2
• Harmonic Law – the square of the
sidereal period of a planet is proportional
to the cube of its semimajor axis
• T2 = k R3
• T = period (time of one revolution)
• R = length of semimajor axis
• k = constant (same for all planets) =
1y2/AU3
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Section 16.1
• T = 1.87 y
• This is for Mars
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Newton’s Correction
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• Sun – 99.87% of the mass of solar
system
• Of the remaining 0.13%, Jupiter is > 50%
• Planets with orbits smaller than earth are
classified as “inferior”
• Planets with orbits larger than earth are
classified as “superior”
Section 16.1
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Revolution/Rotation
•
Section 16.1
Our Solar System
• T2 = k R3 (Kepler’s)
4π2
• T2 = (m + m )G x R3 (Newton’s)
1
2
• This correction takes into account the
mass of the bodies and their
gravitational attraction
• Rearranging the above equation will
give 
2
2
• (m1 + m2) T 3 = 4π
R
G
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Section 16.1
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Section 16.1
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Planet Classification
All planets revolve (orbit) counterclockwise (prograde motion)
around the sun as observed from the north pole. Each planet also
rotates counterclockwise on its axis except Venus and Uranus
(retrograde motion).
• Terrestrial planets – Mercury, Venus,
Earth, Mars
– High percent of more massive (nongaseous) elements
• Jovian planets - Jupiter, Saturn,
Uranus, Neptune, and Pluto (?)
– High percent of less massive gaseous
elements
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Section 16.1
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The Solar System
Inclination of the planets’ orbit to earth’s
The Solar
System -drawn to scale
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Section 16.1
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A Planet’s Period
Section 16.1
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Section 16.1
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Mercury
• Sidereal Period – the time interval
between two successive conjunctions
as observed from the sun
• Synodic Period – the time interval
between two successive conjunctions of
the planet with the Sun as observed
from earth
• Sidereal = P1  P1 = 88 Earth Days
• Synodic = P1  P1  P3= 116 Earth Days
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Section 16.1
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Composition of the Earth
Planet Earth
• Atmosphere – 21% oxygen
• Earth’s crust – over 90%, by volume, of
the rocks/minerals are oxygen!
• We live in an oxidized environment
• Examples of very common minerals at
the earth’s surface include:
• The Earth is the third planet from the
sun, and is a solid, spherical, rocky
body with oceans and an atmosphere
• Large amounts of surface water in all
three phases – solid, liquid, and gas –
exist on Earth
• An oxygen-containing atmosphere,
temperate climate, and living organisms
all make Earth a unique planet
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Section 16.2
– Quartz – SiO2, Calcite – CaCO3, Feldspar –
KAlSi3O8
• Note that most common minerals have
oxygen (O) in their formula
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Section 16.2
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Earth’s Shape
Albedo
• The planet Earth is not a perfect sphere,
but rather an oblate spheriod
• Albedo – the fraction of the incident
sunlight reflected by an object
• Earth’s albedo is 33%
• Moon’s albedo is 7% (from Earth the
moon is the 2nd brightest object in the
night sky)
• Venus’ albedo is 76% (3rd brightest is
sky)
• Since the Moon is so close to Earth it is
brighter than Venus
– Flattened at the poles
– Bulging at the equator
– Due to rotation about its axis
• Pole Diameter is about 43 km less than
the Equatorial Diameter
– Since the earth has an average diameter of
12,900 km this difference is only a small
fraction
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Section 16.2
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Earth Motions
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Earth’s Rotation on its Axis
• Not generally accepted until 19th century
• Very difficult to prove
• 1851, experiment designed by French
engineer, Jean Foucault
• The Foucault Pendulum – very long
pendulum with a heavy weight at the end
• Basically, the Foucault pendulum will
swing back and forth as the earth moves
under it
• Daily Rotation on its axis (daily cycle)
– Rotation – spin on an internal axis
• Annual revolution around the sun
(annual cycle)
– Revolution – movement of one mass
around another
• Precession – the slow change of the
earth’s rotational axis (now at 23.5o) –
chapter 16
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Section 16.2
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Foucault Pendulum
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Section 16.2
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Terrestrial Planets
The pendulum does not
rotate with reference to the
fixed stars. Experimental
proof of the earth’s rotation
• The terrestrial planets include: Mercury,
Venus, Earth, Mars
• Due to physical/chemical characteristics they
resemble Earth
• All four terrestrial planets are
– Relatively small in size and composed of rocky
material and metals
– Relatively close together and close to Sun
– Have no rings
– Only Earth and Mars have moons
– Only Earth has surface water and oxygen
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16.2
Section 16.2
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Section 16.3
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Mercury
• Mercury is the closest planet to the sun
• Mercury has the shortest period of revolution
(88 days), and is the fastest moving
• Mercury was named by the early Greeks after
the swift messenger of the gods
• Temperatures on Mercury range from about
473oC on the side facing the sun to about 173oC on the dark side
• Due to its small size and closeness to the
sun, Mercury has practically no atmosphere
The
Terrestrial
Planets,
Jovian
Planets, and
Earth's Moon
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Section 16.3
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Mercury, a Terrestrial Planet
Section 16.3
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Venus
• Venus is the closest planet to Earth
• Venus is the third brightest object in the sky
• Due to its brightness it was named after
Venus the goddess of Beauty
• The surface of Venus cannot be seen from
Earth, due to dense, thick clouds that cover
the planet
• Magellan radar images indicate that the
surface of Venus is composed of black, hot
rock
– Most surface rocks appear to be volcanic
Rotates 3 times while circling the Sun twice
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Section 16.3
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The Atmosphere of Venus
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Section 16.3
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Venus, a Terrestrial Planet
• Venus’ atmosphere is composed of 96% CO2
• It is so dense that the surface of Venus has a
pressure of 90 atm
• The large percent of CO2 in the atmosphere
results in high surface temperatures (477o C)
due the “greenhouse effect”
• Radar images have revealed relatively few
impact craters
– Most of these craters are fairly large, because the
smaller incoming objects are consumed by
Venus’s thick atmosphere
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Section 16.3
Atmosphere rotates faster than solid planet.
Retrograde rotation possibly caused by impact??
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Section 16.3
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Mars
Martian Volcano – Mt. Olympus
• Mars has a red color, as viewed from
the Earth, and was named for the
Roman god of war
• The surface of Mars has two
outstanding features that have intrigued
scientists for decades; polar ice caps
and extinct volcanoes
• The ice caps are composed of frozen
CO2 in the winter and CO2 vapor with
frozen water in the summer
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Section 16.3
• The largest
known
volcano in
the solar
system, at
24 km in
height, it is
about three
times that of
Mauna Loa
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Section 16.3
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Section 16.3
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Mars – Valles Marineris
This canyon on Mars is
4000 km in length and 6
km deep
Mars, a
Terrestrial
Planet
Geologists think that it is
a crustal fracture caused
by internal forces
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Section 16.3
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Formation of the Terrestrial Planets
The Jovian Planets
• Jupiter, Saturn, Uranus, Neptune
• Much larger than the terrestrial planets
• Composed mainly of hydrogen and helium
• The two least massive elements – H &
He – were the most abundant when the
planets started to coalesce about 5
billion years ago
• Due to the heat from the sun most of
these less massive elements escaped
the gravitational pull of the inner planets
– The four Jovian planets have a very low average
density (approximately 1.2 g/cm3)
• All four are thought to have a rocky core
composed of iron and silicates
• Thick layers of frozen methane, ammonia,
and water are found above the core
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– Leaving behind more of the massive
elements and resulting in thick rocky cores
and higher densities for the inner planets
Section 16.4
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Section 16.4
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Formation of the Jovian Planets
Jupiter
• The four large outer planets were much
farther from the sun and therefore much
colder
• The Jovian planets retained most of
their H and He which now surround their
ice layers and innermost rocky cores
• As a consequence the Jovian planets
have a much lower average density
• Largest planet of the solar system, in both
volume and total mass
• Named after the supreme Roman god of
heaven because of its brightness and giant
size
• Diameter is 11 times Earth’s -- 318 times more
mass than Earth
• The average density of Jupiter approximately
1.3 g/cm3
• Jupiter is covered with a thin layer of clouds
composed of hydrogen, helium, methane,
ammonia, and several other substances
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Section 16.4
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Jupiter
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Section 16.4
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Jupiter’s Great Red Spot (“eye”)
• The Great Red Spot
has erratic movement,
shape, color, and size
– sometimes even
disappearing
• Likely a huge
counterclockwise
“hurricane-like” storm,
lasting hundreds of
years
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Section 16.4
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Saturn
Section 16.4
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Section 16.4
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Saturn
• Distinctive system of three prominent rings
– Rings are inclined 27o to orbital plane
• The rings are thought to be composed of ice
and ice-coated rocks (micrometers  10 m)
• Most spectacular sight that can be viewed
from Earth with a small telescope
• Diameter is 9 times Earth’s -- 95 times more
mass than Earth
• Average density of only 0.7 g/cm3
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Roche Limit (Tidal Stability Limit)
Formation of Saturn’s Rings
• Orbiting moons are held together by their
gravity
• As a moon comes closer to a planet the
differential gravitational (tidal) force on it
increases
• As a moon is brought closer, a point is
reached where the tidal force is greater than
the internal gravitational forces holding the
planet together – and the moon is torn apart
• This critical distance is called the Roche limit
• Saturn’s rings are thought to have
originated as small moons that came
within their Roche limit and were torn
apart
• The Roche limit of Saturn is
approximately 2.4 times the planet’s
radius
• Saturn’s outer ring is located at a
distance of 2.3 times the planet’s radius
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Section 16.4
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Section 16.4
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Uranus
• Discovered in 1781 by William Herschel
(1738-1822), an English Astronomer
• Named after Uranus, the father of the
Titans and the grandfather of Jupiter
• Thin ring system composed of bouldersize particles (>1m), with very little dustsize
• Average density of only 1.3 g/cm3
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Section 16.4
Uranus
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Neptune
Neptune
• Discovered in 1846 by Johann Galle, a
German astronomer
• Englishman John Couch Adams and
Frenchman U.J.J. Leverrier were
mathematicians using Newton’s law of
gravitation
• They noted that Uranus’ motion was
disturbed and predicted the location of
another planet – this is how Galle
eventually discovered Neptune
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Section 16.4
• Neptune also has a large dark spot
similar to Jupiter’s and thought to be the
result of large wind systems
• Neptune and Uranus are similar in size
and in the composition of their
atmospheres
• In many respects these two planets can
be considered twins
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Pluto
• Names for the god of outer darkness
• Average density of only 1.65 g/cm3
• Discovered in 1930, by C.W. Tombaugh
Neptune
– Investigating discrepancies in the orbital
path of Neptune and Uranus
• Does not resemble either the terrestrial
or Jovian Planets
• Pluto is the only planet that has not
been visited by a space probe
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Section 16.4
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Pluto
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Section 16.4
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Section 16.4
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Pluto and its Satellite Charon
• There are similarities between Pluto and
Triton, of Neptune’s moons
• Some scientists think that both are large
asteroids captured from interplanetary
space
• If this is the case, Pluto has maintained
its own orbital path, and Triton was
captured by Neptune
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Section 16.4
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Origin of the Solar System
Major Questions Concerning Solar System
• Any theory that purports to explain the
origin and development of the solar
system must account for its present
form
• According to our best measurements,
our solar system has been in its present
state for about 4.5 billion years
• A valid theory for solar system formation
– must be able to explain a number of
major properties of our solar system
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Section 16.5
• Origin of material?
• Forces that formed the solar system?
• Isolated planets, circular orbits, in same
plane?
• Revolution (orbit) in the same direction?
• Most Rotate in same direction (except two)?
• Terrestrial versus Jovian planets?
• Origin of the asteroids?
• Origin of comets and meteoroids?
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Formation of the Solar System
• Began with a large, swirling volume of cold
gases and dust – a rotating primordial nebula
• Contracted under the influence of its own
gravity – into a flattened, rotating disk
• Further contraction produced the protosun
and eventually accreted the planets
• As particles moved inward, the rotation of the
mass had to increase to conserve angular
momentum (like an ice skater bringing in her
arms)
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Section 16.5
The
Formation of
the Solar
System
Condensation
Theory
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Other Planetary Systems
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• A star with a large planet orbiting about it will
have a small wobble superimposed on its
motion as a result of gravitational effects
• This change in motion (the wobble) is likely to
be very slight, but in some cases may be
detected as a Doppler shift of the star’s
spectrum
– In other words, we should be able to find clouds of
gas and dust, primordial nebula, and protosuns,
etc.
• We should also be able to use gravitational
effects to detect small wobbles in rotational
objects in space
Section 16.6
– As the star approaches the observer, the
wavelengths are compressed (‘blue shift’)
– As the star move away from the observer, the
wavelengths are lengthened (‘redshift’)
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Section 16.6
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System First Planets Discovered
Beyond our Solar System
Gravitational Effects
• In 1992, using the Arecibo Observatory in
Puerto Rico, astronomers reported the
discovery of two objects revolving about a
pulsar
• The amount of wobble can be used to
determine the planet’s mass (related to
gravitational pull)
• The wobble’s cycle time can be used to
determine the orbital period
• Once the orbital period is known,
Kepler’s third law (T2= kR3)can be used
to determine the planet’s average
distance from the star
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Section 16.5
Gravitational Effects
• Are there other planetary systems in the
universe?
• If so, we would expect to find some of these
systems in different stages of formation
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Section 16.6
– Pulsars are very dense, rapidly rotating stars
– Pulsars have a very precise rotation period
– If the rotation period is disrupted, this would
indicate the presence of an object rotating about
the pulsar
• These two objects are the first planets
detected beyond our solar system
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Section 16.6
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Planets Beyond our Solar System
The Moon
• There have now been approximately 80
planets detected around other stars
• These findings strongly indicate the
existence of many other planetary
systems in the universe
• Scientists are also searching for signals
from extraterrestrial intelligence (SETI)
• Equipment today is being used to scan
wide frequency ranges over vast areas
of the sky
• Second brightest object in the sky
• First manned lunar landing on July 20, 1969
• 5 other lunar landings – Apollo 12, 14, 15, 16, &
17.
• Lunar material: by radiometric dating
techniques
– Mountain rocks – 4.4 to 3.9 billion years old
– Plain rocks – 3.9 to 3.1 billion years old
• No rocks older than 4.4 or younger than 3.1
billion years old have been found.
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General Features
• Revolution 29.5 days
• Rotation 29.5 days
• 5th largest moon (largest for the
Terrestrial planets)
• Mass 1/81 Earth
• Gravity 1/6 Earth
• No magnetic field
Surface Appearance
• Craters: 30,000 & up to 100’s kms; likely formed by meteorite
impacts between 4.4 and 3.9 billion year ago.
• Basins: flattened floors of larger craters
• Plains: large, dark, flat areas on the moon believed to be
craters formed by meteorite impact that then filled with
volcanic lava; also called maria; surface covered by a layer of
loose debris called regolith; similar to Earth’s volcanic rock
• Rays: bright streaks extending outward from some craters
• Rills: long, narrow trenches or valleys due to moonquakes
• Mountains: as high as 6100 m (>19,000 ft) and appear to be
formed in a circular pattern, bordering the lunar plains
• Fault - a break or fracture in the surface of the moon, along
which movement has occurred
Composition of the Moon
•
•
•
•
•
Core, mantle, crust
All thought to be solid
Crust, thicker on one side
Presently does not have a magnetic field
Although, the rocks brought back show some
magnetism, indicating that the moon had a
slight magnetic field at the time of rock
crystallization.
Craters on the Moon
Crater
Rays
Basin
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The Straight Wall
•
Rill
Fault Wall
•
A unique steep
slope
The fault wall is
130 km long by
0.25 km in height.
Lunar Motion Effects
•
–
•
•
Relative Motions of the Moon and Earth
Nodes: Two points at which the
Moon’s path crosses the Earth’s
ecliptic plane
Moon Phases
• Waxing: Illuminated portion grows larger
• Waning: Illuminated portion grows smaller
• New moon: Occurs for a short time while moon is on same
meridian as Sun
• Waxing crescent phase; 4 days
• First quarter: 90° East of Sun; 7 days
• Waxing gibbous phase; 10 days
• Full moon: 180° east of sun; 14 days
– Earth position between the Moon and the Sun
• Waning gibbous phase, 18 days
• Last quarter: 270° east of sun; 22 days
• Waning crescent phase, 26-28days
Orbital plane
Approximately 5o with respect to earth’s
orbital plane.
Hence, it is possible for the moon to be
directly overhead at any latitude between
28.5oN and 28.5oS.
Both the earth’s rotation on its axis and the
moon’s revolution around the earth are
counterclockwise (from a N pole perspective).
Albedo
• Fraction of incident
sunlight reflected by a
surface
• Moon’s albedo 0.07
• Earth’s albedo 0.33
Phases of Moon
~ 29.5 days
8 different phases
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Phases of the Moon
As observed from any latitude north of 28.5oN
Phases of the Moon
The “observer” is looking south; therefore east is on the left.
Eclipses
•
•
–
•
–
The shadows cast by the Earth and the Moon
cast two different degrees of darkness
Umbra – the darkest and smallest region
A total eclipse occurs within the umbra region
Penumbra – the semidark region
A partial eclipse occurs within the penumbra
region
Solar Eclipses
Positions of the Sun, Moon, and
Earth During a Total Solar Eclipse
The umbra and penumbra are,
respectively, the dark and semidark
shadows cast on the Earth by the Moon
• Sun: Moon: Earth
• Moon in “new” phase
Lunar Eclipse
Moon is near “full” phase
Sun: Earth: Moon
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