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Final Exam Review
Astronomy 111
Review
• Remember: don’t memorize facts,
understand concepts
p
• The final is comprehensive, but will
stress the material we covered in the
last few weeks of class more
ASTR111 Lecture 7
Earth and Moon
• Cause of seasons
• Understand the relative orientation of
the Earth, Moon, Sun
• Understand what causes solar and
lunar eclipses
• Know
K
what
h t causes tides
tid
ASTR111 Lecture 7
History
• Define: retrograde, epicycle
• Geocentric vs
vs. Heliocentric
• Understand the layout of the Solar
System and be able to make predictions
based on observations
ASTR111 Lecture 7
Kepler and Galileo
• Define: ellipse, semimajor axis, period,
eccentricity,
y, aphelion,
p
, perihelion
p
• Know the implications of Kepler’s Laws
• Know the implications of Galileo’s
Galileo s
observations
ASTR111 Lecture 7
Newton
• Define: velocity, acceleration, force,
orbital speed,
p
, escape
p velocity,
y, angular
g
momentum
• Know what Newton’s
Newton s laws tell us
• Be able to use the Newton’s equations
to solve problems
ASTR111 Lecture 7
Light
• Define: light-year, spectrum
• Energy of a photon
• Know the relative wavelengths of light in
the spectrum
• What causes an emission or absorption
li iin a spectrum?
line
t
?
• What do spectral lines tell us?
ASTR111 Lecture 7
Light
• Define: blackbody, temperature
• Understand Kirchoff’s laws
• How does temperature of a star relate
to color?
• Be able to use
– Wien’s law
– Stefan-Boltzmann law
– Inverse-square law of brightness
• Use Doppler effect to calculate speeds
ASTR111 Lecture 7
Telescopes
• Whay are larger telescopes better?
• Why do some telescope need to fly in
space?
– Atmospheric effects (absorption and
blurring)
• What are telescopes in remote
locations?
• What is the ultimate limit of the angular
resolution
l ti off a telescope?
t l
?
ASTR111 Lecture 7
Solar System Formation
• Solar System formed from rotating cloud of gas &
dust
• Conservation of angular momentum caused flattening
into disk
• Planetesimals condensed and collided to form planets
• Happened about 4.5 billion years ago
• Hotter closer to yyoung
g Sun,, cooler farther out in
disk
• Materials like rock and iron/nickel condensed in inner
solar system
• Icy materials in outer solar system
• Our Solar System is not unique
• Thousands of other planets now known around stars
ASTR111 Lecture 7
Terrestrial Planets
• M
Mercury, Venus,
V
E th & M
Earth,
Mars are similar
i il
in composition
• Small and rocky/iron
• Have varying atmospheres and geological
activity
• Only Earth has a significant Moon
• The Moon!
• Probably formed from an early collision
ASTR111 Lecture 7
Jovian Planets and other stuff
• Jupiter, Saturn, Uranus, and Neptune are all much
more massive than Earth
• Primarily composed of H and He
• Most of the rest is water, methane, ammonia, and
carbon dioxide (based)
• Some small rocky/iron material in core
• Consequence of formation location
• Jupiter and Saturn are still “collapsing” and
releasing heat
• All have moons
• Some are large, most are captured asteroids
• Pluto is an example of a “dwarf planet”
• There are many more!
ASTR111 Lecture 7
Jovian Planets and other stuff
• Asteroids are mainly found between Mars and
Jupiter
• Remnants of a planet that did not form
• Mostlyy rockyy and iron/nickel
• Comets are also remnants
• Icy leftovers in the outer solar system
• Some
S
rocky
k material
i l as wellll
• Spectacular displays are icy material “boiling” off
as they get close to Sun
• If either a large asteroid or comets hits Earth it
would be a disaster!
• Possibly
P
ibl what
h t kill
killed
d off
ff th
the di
dinosaurs
ASTR111 Lecture 7
Distances to Stars
• Distance is important but hard to measure
for objects outside the solar system
• Trigonometric parallaxes
– direct geometric method
– only good for the nearest stars (~500pc)
• Units of distance in Astronomy:
– Parsec (Parallax second)
– Light Year
ASTR111 Lecture 7
Luminosity and Brightness
• Luminosity of a star:
– total energy
gy output
p
– independent of distance
• Apparent brightness of a star:
– depends on the distance by the inversesquare law of brightness.
– measured quantity from photometry.
ASTR111 Lecture 7
Stellar Masses and Radii
• Types of binary stars
– Visual
– Spectroscopic
– Eclipsing
• Only way to measure stellar masses:
– Only roughly a few hundred stars
• Radii are measured for
f few
f
stars.
ASTR111 Lecture 7
Stellar Colors and Spectra
• Color of a star depends on its
Temperature
– Red Stars are Cooler
– Blue Stars are Hotter
• Spectral Classification
– Classify stars by their spectral lines
– Spectral differences mostly due to
Temperature
• S
Spectral
t l Sequence
S
(T
(Temperature
t
Sequence)
• O B A F G K M L T
ASTR111 Lecture 7
HR Diagram and ML Relation
• The Hertzsprung-Russell (H-R) Diagram
– Plot of Luminosity
y vs. Temperature
p
for stars.
• Features:
– Main Sequence
q
((most stars))
– Giant & Supergiant Branches
– White Dwarfs
• Luminosity Classification
Mass-Luminosity
Luminosity Relationship
• Mass
ASTR111 Lecture 7
Physics of Stars
• Observational Clues to Stellar Structure:
–H
H-R
R Diagram
– Mass-Luminosity Relationship
– The Main Sequence is a sequence of Mass
ASTR111 Lecture 7
Physics of Stars
• Stars shine because they are hot.
– need an energy source to stay hot.
• Kelvin-Helmholtz Mechanism
– Energy
gy from slow Gravitational Contraction
– Cannot work to power the present-day Sun
• Nuclear Fusion Energy
gy
– Energy from Fusion of 4 1H into 1 4He
– Dominant p
process in the p
present-dayy Sun
ASTR111 Lecture 7
Stellar Interiors
• Energy generation in stars:
– Nuclear Fusion in the core.
– Controlled by a Hydrostatic “thermostat”.
• Energy is transported to the surface by:
– Radiation & Convection in normal stars
– Conduction in white dwarf stars
• With Hydrostatic Equilibrium, these
determine the detailed structure of a star.
ASTR111 Lecture 7
Stellar Interiors
• Stars are held together by their selfg
gravity
y
• Hydrostatic Equilibrium
– Balance between Gravity & Pressure
• Core-Envelope Structure of Stars
– Hot,
H t dense,
d
compactt core
– cooler, low-density, extended envelope
ASTR111 Lecture 7
Main Sequence
• Main Sequence stars burn H into He in
their cores.
• The Main Sequence is a Mass
Sequence.
– Lower M-S: p-p chain, radiative cores &
convective envelopes
– Upper M-S: CNO cycle, convective cores &
radiative envelopes
• Larger Mass = Shorter Lifetime
ASTR111 Lecture 7
ASTR111 Lecture 7
Post-Main Sequence Evolution
•Stage:
•Energy Source:
•Main Sequence
•Red Giant
•Horizontal Branch
•Asymptotic
y p
Giant
•White Dwarf
•H Burning Core
•H Burning Shell
•He Core + H Shell
•He Shell + H Shell
•None!
ASTR111 Lecture 7
Post-Main Sequence Evolution
• End of the Life of a Massive Star:
– Burn H through Si in successive cores
– Finally build a massive Iron core
• Iron core collapse & core bounce
• Supernova explosion:
– Explosive
E l i envelope
l
ejection
j ti
– Main sources of heavy elements
ASTR111 Lecture 7
ASTR111 Lecture 7
Compact Stellar Remnants
• White Dwarf:
– Remnant of a star <8 Msun
– Held up by Electron Degeneracy Pressure
– Maximum Mass ~1.4 Msun
• Neutron Star:
– Remnant of a star < 18 Msun
– Held up by Neutron Degeneracy Pressure
– Pulsar = rapidly spinning neutron star
ASTR111 Lecture 7
Black Holes
• Black Holes are totally collapsed objects
– gravity so strong not even light can escape
– predicted by General Relativity
• Schwarzschild Radius & Event Horizon
• “Unobservable” objects are observable through
their effect on surroundings
– X-ray binarys
– Jets
– Orbital mechanics
• Black Hole Evaporation
– Emit "Hawking Radiation"
ASTR111 Lecture 7
Clusters of Stars
• H-R Diagrams of Star Clusters
• Ages from the Main
Main-Sequence
Sequence Turn-off
Turn off
• Open Clusters
– Young clusters of few 1000 stars
– Blue Main-Sequence stars & few giants
• Globular Clusters
– Old clusters of a few 100,000 stars
– No blue Main-Sequence
Main Sequence stars & many
giants
ASTR111 Lecture 7
Galaxies
• Three basic types of galaxies:
– Spirals
• Disk and spheroid component
• Rotation of disk allows measurement of galaxy mass
– Ellipticals
– Irregulars
• Differ in terms of
– Relative
R l ti gas content
t t
– Star formation History
– Internal motions
• Galaxies tend to group into Clusters
– Groups, clusters, and superclusters
– Galaxies can collide and merge
• Some galaxies have “active” nuclei
– Powered
P
db
by llarge bl
black
kh
holes
l iin th
the center
t
ASTR111 Lecture 7
Cosmology
• Cosmological Principle:
– The Universe is Homogeneous and
Isotropic on Large Scales.
– No special
p
p
places or directions.
• General Relativity predicts an
expanding universe.
universe
• Cosmological Constant
ASTR111 Lecture 7
The Big Bang
• Big Bang model of the Universe
– Starts in a hot, dense state
– Universe expands and cools
• Expansion and redshift
• Critical density
– Geometry
G
t off the
th Universe
U i
• Hubble time = maximum age of the
Universe
ASTR111 Lecture 7
The Big Bang
• Fundamental tests of the Big Bang
• Primordial nucleosynthesis
– Primordial Deuterium & Helium
– Primordial light elements (Li
(Li, B
B, Be)
• Cosmic background radiation
– Relic
R li blackbody
bl kb d radiation
di ti ffrom Bi
Big B
Bang
– Temperature: T = 2.726 K
ASTR111 Lecture 7
Fate of the Universe
• The Fate of the Universe depends on
the density
y of matter.
• Closed Universe:
– Enough matter to stop the expansion
– Collapses in a “Big Crunch”
• Open Universe:
– Expands forever
– Ends in a cold,
cold disordered state
state.
ASTR111 Lecture 7
Fate of the Universe
• The Universe is composed of mainly
Dark Matter and Dark Energy
gy
• We live in a flat Universe that will
expand forever
ASTR111 Lecture 7