Astronomy 103
Review Lecture
Final Exam:
10:05 A.M. TUE. DEC 18
Chamberlin 2301
13 Dec 2007
Reminders
• Pick up all homework and discussion handouts that
you haven’t gotten back from me!
• If any HW wasn’t returned, YOU are responsible for
making sure grade was recorded!
• TA Review Session (all Q&A)
– 6pm-8pm Friday December 14th
– Chamberlin 2241
• New stuff: Units 54, 55, 57-68,70-72, 74-84. Old
material: Units 1-30, 49-52.
• Katie is GONE and may not have email access after
the 15th.
13 Dec 2007
Helpful items on my website:
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Equation Sheets from Exam 1 & 2
Practice Questions from Exam 1
Exam 2 Review Lecture
Homework Solutions
(NEW!) Review questions for new
material
• (NEW!) This review lecture
13 Dec 2007
Topics to Review - Part 1
• The basics: metric system, unit conversion, scientific
notation, size scales
• Earth, Moon, Sun, Solar System, Milky Way overview
• Special Units: Parsec, AU, light year, etc
• Celestial Sphere
• Causes of: Days, seasons, phases of moon,
precession, eclipses, retrograde and prograde motion
of planets
– Why do days get shorter in winter, why is it colder, etc?
• Solar v. Sidereal day
13 Dec 2007
Topics to Review - Part 1
• How did we first determine the shape and size of the
earth? The moon? The sun? Who made those
discoveries?
• Geocentric v. Heliocentric models of the solar
system- how did we decide?
• Angular diameter - what is it, how is it related to an
objects real size (linear diameter) and its distance
from us?
• How were distances to other planets measured (and
who measured them)?
• What did Brahe, Kepler, Galileo, Newton contribute to
astronomy?
• Tides - cause, timing of high and low tide
13 Dec 2007
Topics to Review - Part 1
• IMPORTANT TO UNDERSTAND BASIC PHYSICS
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Kepler’s Laws
Newton’s Laws (inertia, F=ma, equal and opposite reactions)
Gravity, Newton’s Universal Law of Gravitation
Surface Gravity
Circular motion and orbits
Centripetal Force
How to get masses from orbital speeds
Escape Velocity
Conservation of energy, kinetic energy, potential energy
Conservation of angular momentum
• Check out your equation sheet from Exam 1!
13 Dec 2007
Angular Size
13 Dec 2007
I drop a 10kg mass and a 5kg mass from 4
feet off of ground.
When to they hit?
a. same time
b. 10 kg mass hits first
b. 5 kg mass hits first
WHY? Hint: What is difference between
mass and weight? Does acceleration due
to gravity depend on mass?
13 Dec 2007
How do you calculate the mass of a star if you can
measure the orbital velocity of a planet orbiting around
it?
GM
Vcirc 
d
3
MA  MB 

13 Dec 2007
a AU
PYR2
What happens if the string breaks? (INERTIA!)
13 Dec 2007
Calculating Escape Velocity
• From Newton’s laws of
motion and gravity, we
can calculate the
velocity necessary for
an object to have in
order to escape from a
planet, called the
escape velocity
2GM
Vesc 
R
13 Dec 2007
Topics to Review - Part 2
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Nature of Light
Blackbodies
Kirchoff’s Laws
Doppler Shift
Telescopes
Parallax
Sun
– Parts of the sun
– Hydrostatic equilibrium (“sun’s thermostat”)
– Sun’s source of energy (fusion)
http://www.astro.wisc.edu/~devine/exam2review.ppt
13 Dec 2007
Topics to Review - Part 3
• Luminosity of stars-- Stefan Boltzman’s Law
• HR Diagrams, Stellar evolution
• End stages of stars -- white dwarfs, neutron stars,
black holes
• Active Galactic Nuclei
• Galaxy types, and how galaxies form
• Interstellar medium
• Standard candles and distances
• Cosmology
– Big bang, expansion, Hubble Law
– Structure of universe, CMB, how did matter form?
– Fate of universe
• Other life in the universe?
13 Dec 2007
Star Formation
13 Dec 2007
Tracking changes with the
HR Diagram
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As a star evolves, its
temperature and
luminosity change.
We can follow a stars
evolution on the HR
diagram.
Lower mass stars move
on to the main
sequence, stay for a
while, and eventually
move through giant
stages before
becoming white dwarfs
Higher mass stars
move rapidly off the
main sequence and
into the giant stages,
eventually exploding in
a supernova
13 Dec 2007
Tracking changes with the
HR Diagram
• 0.5-8 solar masses:
WD
• 8-25 solar masses:
Neutron star
• > 25 solar masses:
black hole
• >50 solar masses what do you think?
• What about “quark
stars”?
13 Dec 2007
The Hourglass Nebula
13 Dec 2007
Neutron Stars (Pulsars)
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A neutron star spins very rapidly
about its axis, thanks to the
conservation of angular
momentum
If the neutron star has a
magnetic field, this field can
form jets of electromagnetic
radiation escaping from the star
13 Dec 2007
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As the neutron star spins, the
jets can sweep past earth,
creating a signal that looks like
a pulse.
Neutron stars can spin very
rapidly, so these pulses can be
quite close together in time!
Black Holes
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If a stellar core is
massive enough, it
will not stop
collapsing when it
becomes a neutron
star.
Once something,
including a photon,
crosses the
Schwarzschild radius
(or event horizon),
escape is impossible.
Can Hawking
Radiation Escape?
13 Dec 2007
Milky Way
13 Dec 2007
Spiral Galaxies
13 Dec 2007
Elliptical Galaxies
13 Dec 2007
Irregular Galaxies
13 Dec 2007
Active Galactic Nuclei &
Quasars
• Quasars are small, extremely
luminous, extremely distant
galactic nuclei
• Luminosity and jets likely
come from matter falling
into big black hole (millions
of solar masses) at the
galaxies centers
• Was our galaxy an AGN
once?
13 Dec 2007
Mass Transfer and Novae
13 Dec 2007
The Chandrasekhar Limit
and Supernovae
13 Dec 2007
Type 1a Supernova – Another
standard candle!
• Variable stars
are also
standard
candles-- how,
why?
• Um, what’s a
standard
candle? Why
do they
matter?
13 Dec 2007
Large Scale Structure in the
Universe
• Galaxies tend to form
long chains or shells
in space, surrounded
by voids containing
small or dim galaxies
• This is as far as we
can see!
13 Dec 2007
The Hubble Law
• In 1920, Edwin Hubble
developed a simple
expression relating the
distance of a galaxy to
its recessional speed.
• V=Hd
– V is the recessional
velocity
– D is the distance to
the galaxy
– H is the Hubble
Constant (70 km/sec
per Mpc)
13 Dec 2007
• This was our first clue
that the universe is
expanding!
A Timeline of the Universe
13 Dec 2007
Clumpiness in the CMB
13 Dec 2007
The Origin of Helium
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13 Dec 2007
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Immediately after the Big
Bang, only protons and
electrons existed
Shortly after the BB,
temperature and density
was high enough for
deuterium to form by
fusion
After 100 seconds or so,
temperature cooled
enough so that deuterium
could fuse into helium
nuclei
The temperature
continued to cool, and
fusion stopped after a few
minutes.
Big Bang theory predicts
that around 24% of the
matter in the early
Density of the Universe
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Like throwing a ball in the
air-- if you throw it with
enough energy to get past
the density of earth (so it
goes faster than escape
velocity), the ball will go on
traveling into space forever
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Similarly, the density of the
universe and the energy
provided by big bang
determine its ultimate fate
• This confusing graph shows the possible options- expand forever, become stable and stop
expanding, or start collapsing… OR….
13 Dec 2007
The Universe is ACCELERATING
Apart?!?
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In our ball example, this
would be like throwing a ball
in the air, and watching it get
FASTER as it got further away
from you. Where is that extra
energy coming from?
13 Dec 2007
• DARK ENERGY
– Not yet well understood
or explained. Stay
tuned…
Other Possible Curvatures of
Space
• In addition to a closed, or positive curvature
of space, there are two other options
– Space could be flat, or have zero curvature
– Space could be curved away from itself, or have
negative curvature
– Geometry behaves differently with each curvature!
13 Dec 2007
21 cm Radiation
• Most interstellar gas is very
cold, so it emits very few
photons.
• The electron in a hydrogen
atom has two energy states
– Spin up and spin down
– Spin up has slightly more
energy than spin down
13 Dec 2007
• If the electron’s spin flips
from up to down, it must emit
a photon of the same energy
as the energy difference
between states
• This 21 cm radiation (HI
emission) is detected by
radio telescopes, allowing the
Gravitational Lenses
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13 Dec 2007
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Dark matter warps space just like
ordinary matter does
The path of light rays bends in the
presence of mass
A galaxy or other massive object can
bend and distort the light from objects
located behind it, producing multiple
images
This is called gravitational lensing
Life Elsewhere?
Drake Equation
Probability of life on other
planets=?
13 Dec 2007