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Physics 320: Astronomy and
Astrophysics – Lecture I
Carsten Denker
Physics Department
Center for Solar–Terrestrial Research
NJIT
Introduction
 History
of Solar Physics
 Prehistoric
era
 Ancient Greek
 Paradigm shift in planetary models
 “Modern” Solar Physics
 Why bother … ?
 Most
of the material has been stolen from
the HAO Education Pages by Paul
Charbonneau (NCAR, HAO)
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Stonehenge (3000 – 1600 BC)
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Solar Observations BC
3 May 1375 BC or 5 March 1223 BC: eclipse
record on clay tablet uncovered in the ancient
city of Ugarit, Syria
 8th century BC: Babylonians were keeping a
systematic record of solar eclipses, predictions
based on numerological rules
 800 BC: Oldest record of a sunspot observations
are found in the Book of Changes, China
 250 BC: Measurement of the distance to the Sun
by Aristarchus of Samos (ca. 310-230 BC).

NJIT Center for Solar–Terrestrial Research
September 3, 2003
Ancient Greek


Physical (geocentric) model of
the cosmos by Aristotle (384 –
322 BC)
Mathematical model of
planetary motion by Ptolemy
(100 – 170), terrestrial/celestial
sphere, basic elements: earth,
water air, and fire/quintessence
The Aristotelian cosmos. The Earth
sits motionless at the center of the
universe, and the outer sphere, the
Primum Mobile, is assumed to
undergo a full revolution in 24 hours.
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Early Observations of the Corona



Report of solar eclipse
observations by the Byzantine
historian Leo Diaconus (950 –
994) on December 22nd, 968 from
Constantinople (now Istanbul,
Turkey).
Possible eclipse record on oracle
bones dating from the Shang
dynasty in China (1766 – 1123
BC)
Chronicle of Novgorod describes a
prominence during the May 1st,
1185 solar eclipse: "In the evening
Annales Sangallenses:
"...at the fourth hour of the day ...
darkness covered the earth and all the
brightest stars shone forth. And is was
possible to see the disk of the Sun, dull
and unlit, and a dim and feeble glow like
a narrow band shining in a circle around
the edge of the disk".
there as an eclipse of the sun. It was
getting very gloomy and stars were seen
... The sun became similar in appearance
to the moon and from its horns came out
somewhat like live embers."
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Sunspot Observations



Official records of the
Chinese imperial courts
starting in 165 BC
Theophrastus (374 –287 BC)
including details of umbra
and penumbra
Aristotelian views concerning
the incorruptibility of the
heavens meant that sunspots
were "physically impossible",
sightings were ignored or
ascribed to transit of Mercury
or Venus across the solar disk
NJIT Center for Solar–Terrestrial Research
"... from morning to evening, appeared
something like two black circles within
the disk of the Sun, the one in the upper
part being bigger, the other in the lower
part smaller. As shown on the drawing."
From the Chronicles of John of Worcester:
one of the first surviving sunspot drawing
from a sighting on December 8th, 1128.
September 3, 2003
Nicholas Copernicus
(1473–1543)

De Revolutionibus
Orbium Coelestum in 1543

Heliocentric planetary model:
The Sun is at the center of all planetary
motions, except for the Moon which
orbits Earth. Under this arrangement
the orbital speed of planets decreases
steadily outwards, and the outer sphere
of fixed stars is truly motionless. In
Copernicus' original model the Earth
has three motions: a daily 24-hr axial
rotation, a yearly orbital motion about
the Sun, and a third motion, somewhat
related to precession which Copernicus
thought necessary to properly
reproduce ancient observations.
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Orbital Paths of Planets
Collection of 20 years
of accurate planetary
positions by Tycho
Brahe (1546 – 1601)
 Johannes Kepler (1571
– 1630)




1609: Astronomia
Nova
1619: Harmonice
Mundi
1627: Rudolphine
Tables
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September 3, 2003
Galileo Galilei (1564 – 1642)
First telescopic
observations
of the Sun!
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September 3, 2003
Sun as a Star – Maunder Minimum


René Descartes (1596 –
1650) describes the Sun as
a star in his 1644 book
Principia Philosophiae
Maunder minimum 1645
–1715: sunspots vanish
even though a systematic
solar observing program
was underway under the
direction of Jean
Dominique Cassini (1625
– 1712) at the newly
founded Observatoire de
Paris
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Isaac Newton (1642 – 1727)



1686: Principia
Mathematica, universal
law of gravitation
Stable planetary orbits
result from a balance
between centripetal and
gravitational acceleration
Sun–to–Earth mass ratio
(MEarth/MSun= 28700
instead of 332945), wrong
value for solar parallax,
better estimate in later
edition of the Principia
(within factor of two)
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Infrared Radiation

In 1800, William Herschel (1738 –1822) extended Newton's
experiment of separating chromatic light components via refraction
through a glass prism by demonstrating that invisible "rays" existed
beyond the red end of the solar spectrum.
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Spectroscopy


The English chemist and
physicist William Hyde
Wollaston (1766 – 1828)
noticed dark lines in the
spectrum of the Sun while
investigating the refractive
properties of various
transparent substances
Joseph von Fraunhofer
(1787-1826) independently
rediscovered the “dark
lines” in the solar
spectrum
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Chemical Composition of the Sun
Reproduction of part of the map of the solar spectrum published in 1863 by
Kirchhoff, showing the identification of a large number of spectral lines with
various chemical elements. Note numerous clear matches for Iron (Fe).
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Sunspot Cycle
Heinrich Schwabe
(1789 –1875)
NJIT Center for Solar–Terrestrial Research
September 3, 2003
The First Solar Photograph 1845
The first successful
daguerrotype of the
Sun, reproduced
below, was made on
April 2nd, 1845 by
the French
physicists Louis
Fizeau (1819-1896)
and Léon Foucault
(1819-1868). The
exposure was 1/60
of a second. This
image shows the
umbra/penumbra
structure of
sunspots, as well as
limb darkening.
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Sunspot Numbers


Statistics of sunspot number
by Swiss astronomer Rudolf
Wolf (1816-1893)
Relative sunspot number:
r = k (f + 10 g),
where g is the number of
sunspots groups visible on the
solar disk, f is the number of
individual sunspots (including
those distinguishable within
groups), and k is a correction
factor that varies from one
observer to the next (with k = 1
for Wolf's own observations)
NJIT Center for Solar–Terrestrial Research
Sunspot drawings by Johann
Hieronymus Schroeter (1745 – 1816), an
active solar observer between 1785 and
1795. Schroeter's sunspot drawings
were a primary source for Wolf's
reconstruction of activity cycle number 4
(1785 –1798)
September 3, 2003
Differential Rotation

Richard C. Carrington
(1826 – 1875)

Gustav Spörer (1822 –
1895)
Spörer's Law of sunspot migration. The thick lines shows the latitude] at which
most sunspots are found (vertical axis, equator is at zero), as a function of time
(horizontal axis). The dashed line is the Wolf sunspot number, showing the rise
and fall of the solar cycle.
NJIT Center for Solar–Terrestrial Research
September 3, 2003
First Observation
of a Solar Flare 1859
On September 1st, 1859, the astronomer R. C. Carrington was engaged in
his daily monitoring of sunspots, when he noticed two rapidly brightening
patches of light near the middle of a sunspot group he was studying.
NJIT Center for Solar–Terrestrial Research
September 3, 2003
First Observations of a Coronal
Mass Ejection 1860
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September 3, 2003
The Magnetic Nature
of Sunspots 1908
George Ellery Hale
(1868–1938)
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The magnetically–induced Zeeman splitting
in the spectrum of a sunspot. Reproduced from
the 1919 paper by G.E. Hale, F. Ellerman, S.B.
Nicholson, and A.H. Joy (in The Astrophysical
Journal, vol. 49, pp. 153–178).
September 3, 2003
The Celestial Sphere
Tradition 
 Copernican
Revolution 
 Positions on the
Celestial Sphere
 Physics and
Astronomy
 Greek
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Positions on the Celestial Sphere
Earth precession period is 25,770 years.
   m  n sin  tan   N
   n cos   N
Reference Epoch 1950:
m = 3.07327s yr –1
n = 20.0426’’ yr –1
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Spherical Geometry
Law of sines:
sin a sin b sin c


sin A sin B sin C
Law of cosines for sides:
cos   cos b cos c  sin b sin c cos A
Law of cosines for angles:
cos A   cos B cos C  sin B sin C cos a
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Proper Motion
d  v t
d v
 
 t
r
r
d v


dt
r
v: transverse or tangential
velocity
vr: radial velocity
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Synodic and Sidereal Period
Planet
1/ P  1/ PEarth
1/ S  
1/ PEarth  1/ P
(inferior)
(superior)
NJIT Center for Solar–Terrestrial Research
Sidereal Orbital
Period [yr]
Mercury
0.2408
Venus
0.6152
Earth
1.0000
Mars
1.8809
Jupiter
11.862
Saturn
29.458
Uranus
84.014
Neptune
164.79
Pluto
248.54
September 3, 2003
Retrograde Motion of Planets
NJIT Center for Solar–Terrestrial Research
September 3, 2003
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Zodiac
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September 3, 2003
Physics and Astronomy
 Astronomy
= natural extension of human
curiosity in its purest form
 Paradigm shifts
 Physical causes for observable phenomena
 Astronomy + Physics = Astrophysics
 Observations  analyze photons and
particles
 Tools: telescopes, post–focus
instrumentation, and computers
NJIT Center for Solar–Terrestrial Research
September 3, 2003
Homework
 Homework
is due Wednesday September
10th, 2003 at the end of the lecture!
 Homework assignment: Problems 1.5, 1.6,
and 1.7
 Late homework receives only half the
credit!
 The homework is group homework (2–3
students)!
 Homework should be handed in as a text
document!
NJIT Center for Solar–Terrestrial Research
September 3, 2003