Astronomy
Phys 181
Readings: ASTRONOMY TODAY
Ch 23.1, 23.2
Ch 24.1, 24.2, 24.5
Ch 26
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There was no "before" the beginning of our universe, because once
upon a time there was no time.
* John D. Barrow
Quotes
I don't pretend to understand the Universe--it's a great deal bigger
than I am.
* Thomas Carlyle
A universe that came from nothing in the big bang will disappear into
nothing at the big crunch. Its glorious few zillion years of existence
not even a memory.
* Paul Davies
Anyone informed that the universe is expanding and contracting in
pulsations of eighty billion years has a right to ask, "What's in it for
me?"
* Peter De Vries
Nothing puzzles me more than the time and space; and yet nothing
troubles me less.
* Charles Lamb
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EXAM REVIEW
The final exam will consist of a choice of TWO (2) essays, selected
by the student, from a list of FIVE (5) essay topics chosen by the
professor.
Essays should be a minimum of FOUR (4) bluebook pages in length.
ESSAY TOPICS
•Chronologically discuss key discoveries in the history of Astronomy.
•Describe Kepler’s three laws with particular emphasis on their role
in understanding 
the motions of the planets around the sun.
•A comparison of the evolution and fate of high and low mass stars.
•A description of Einstein’s Principle of Equivalence, its effects, and
predictions regarding Black Holes.
•Give a brief summary of each of the popular possibilities for the
fate of our universe, and suggest the evidence that may support
each.
History of Astronomy:
Kepler’s Laws
1. Each planet moves in an ellipse, with the
sun at one focus.
2. The line between the sun and the planet
sweeps out equal areas in equal times.
3. The ratio of the cube of the average radius
of a planets orbit to the square of its
orbital period of revolution is the same for
each planet. (Harmonic Law)
Kepler’s laws
High and Low mass stars:
Principle of Equivalence:
Essays will be scored on the following criterion:
•Coherence
•Accuracy of information
•Presence of four supporting arguments or evidence from the
lecture or readings.
•Presence of one referenced supporting argument or evidence
from another source.
•Conventional development: Thesis – Support – Conclusion
•Reasonable grammar
Milky Way Galaxy
The Milky Way Galaxy: Vital Statistics
•Diameter - 100,000 light years
•Thickness (Nucleus) - 20,000 light years
•Thickness (Disc) - 2,000 light years
•Number of Stars - 400,000,000,000
•Age - 15,000,000,000 years
Horizon
Horizon
N
Corona Borealis
Serpens
Draco
Hercules
Libra
Centaurus
SW
Horizon Cepheus
Ophiuchus
Lyra
Cygnus
Lupus
Crux
Scorpius
Vulpecula
Norma
Scutum
Sagitta
Cassiopeia
Horizon
Circinus
Aquila
Lacerta
Sagittarius
Delphinus
Telescopium
Corona Australis
Musca
Ara
Triangulum Australe
Pegasus
Capricornus
Apus
Equuleus
NE
Pavo
Microscopium
Aquarius
S
Indus
Octans
Tucana
Pisces
Viewed fr o m:
Equator
75° 09' 21" W
0° 00' 00" N
L o cal tim e:
01:22:31
2007/06/23
JD 2454274.73
Horizon
F ield o f view :
Mag n itu d es: 5.5 4.5 3.5 2.5 1.5 0.5
180° 00' 00"
Single star
Galactic Lon: 029.2226°
Multiple star
Galactic Lat: +00.7212°
Variable star
Piscis Austrinus
Horizon
Viewed fr o m:
Equator
75° 09' 21" W
0° 00' 00" N
L o cal tim e:
01:22:31
2007/06/23
JD 2454274.73
F ield o f view :
180° 00' 00"
Galactic Lon: 029.2226°
Galactic Lat: +00.7212°
Mag n itu d es: 5.5 4.5 3.5 2.5 1.5 0.5
Single star
Multiple star
Variable star
Viewed fr o m:
Equator
75° 09' 21" W
0° 00' 00" N
L o cal tim e:
01:22:31
2007/06/23
JD 2454274.73
F ield o f view :
180° 00' 00"
Galactic Lon: 029.2226°
Galactic Lat: +00.7212°
Mag n itu d es: 9.5 8.5 7.5 6.5 5.5 4.5
Single star
Multiple star
Variable star
The Halo
The Disk
The Core
Elliptical Galaxies
•1/3 of all galaxies
•Giant Ellipticals are the size of our galaxy but are rare
•Dwarf Ellipticals are more common (6000 light yrs across)
Riesen-E
Spiral Galaxies
Largest fraction of galaxies
Andromeda
Barred Spiral Galaxy
NGC-1365
Irregulars
Large Magellanic Cloud
Galaxies form groups or Clusters
Coma Cluster
How do we measure
our universe?
Radar Ranging:
We measure distances in our solar
system by bouncing radio waves off
planets, for example.
Geometry helps us to interpret the
results.
Within one light-hour.
Parallax:
The distances to objects
are determined by observing
apparent shifts with
respect to background
objects.
100 light-years
Main-Sequence Fitting:
We know the distance to the Hades Cluster
in our own galaxy.
Comparing the intensities of main sequence
stars in Hades to the main-sequence stars
of other clusters in our galaxy allows us to
infer their distances.
100,000 light-years
Cepheid Variables:
There is a period-luminosity
relation for Cepheids.
Studying this relationship for
Cepheids nearby allows us to
determine the luminosity of
Cepheids in other, nearby
galaxies.
10,000,000 light-years
Distance Standards:
Luminosities of white dwarfs in nearby
galaxies are determined.
There is a rotational period-luminosity
relation for galaxies allowing us to
determine the luminosities of more
distant galaxies. (Tully-Fisher Relation)
10,000,000,000 light-years
Hubble’s law: v=H*d
>10 Billion light-years
Olber’s Paradox
The universe is expanding!
THE END?