An Unofficial, Abbreviated, Review Synopsis
of Subjects Covered in Astro 150
Topics indicated by (*) might be covered in more depth in Astro 250.
- Gravity: Newton's Laws
- (*) Gravity as a fundamental force: Central, Universal, and
Cosmic
- (*) Other Cosmic forces: Electromagnetic force, Weak
Nuclear force, strong nuclear force
- Light: a form of energy=electromagnetic radiation
- wave nature: wavelength (l) x frequency (f) = speed (c for
light)
- different wavelength = different 'color'
- particle nature: photon as a bundle of light energy; energy
proportional to frequency
- Brightness proportional to luminosity divided by distance
squared
- Electromagnetic spectrum
- short wavelength (gamma ray) to long wavelength (radio)
- high energy (gamma ray) to low energy (radio)
- Thermal (blackbody) radiation - radiation from objects because
they are hot
- Wien's law: wavelength of maximum emission increases with
decreasing temperature
- Stefan-Boltzmann Law: energy emitted proportional to
T4
- stars are like blackbodies; hot stars are blue, cool stars
are red
- Spectral Lines
- Kirchoff's laws: emission, absorption, and continuous
spectra
- discrete atomic energy levels correspond to discrete
electron orbits
- transitions up in energy absorb photons; transitions down
emit photons
- bigger energy difference between levels, higher energy
photon involved
- each element has its own signature spectral lines; atomic
fingerprints
- Spectroscopy as the "Rosetta Stone" in astronomy
- Telescopes: light gathering power and resolution depend on
size
- instrumentation: photometry, spectroscopy, imaging
- The Sun
- surface features: sunspots, prominences, corona, etc.
- energy transport by radiation, conduction and convection
- energy production by nuclear fusion: E=mc2; 4 hydrogen
-> 1 helium + energy
- solar neutrino problem
- Stars
- stellar spectra: hot to cool (=blue to red): O,B,A,F,G,K,M
- distances via trigonometric parallax
- radial velocity: the Doppler effect
- change in wavelength (Dl) divided by wavelength = velocity
in line-of-sight / c
- ranges of luminosity and temperature
- The HR Diagram
- 2-D classification scheme: luminosity versus temperature
(or color)
- main sequence, red giants, white dwarfs
- stellar mass via binary stars
- the main sequence: higher mass = more luminous = bluer =
rarer
- main sequence life time = 10 billion years divided by
mass3
- Star Clusters: key objects for stellar evolution
- associations, open clusters, globular clusters
- stars become red giants when hydrogen exhausted in core
- main sequence peeled down with age
- oldest clusters are 15 billion years old
- Stellar evolution
- (*) star formation in molecular clouds; triggers,
protostellar collapse, nuclear ignition
- main sequence - longest stage
- core H exhaustion - become red giants
- helium ignition - helium flash if mass less than twice sun
- core helium exhaustion: giant branch again
- M < 8 solar - white dwarf exposure and planetary nebula
formation
- M > 8 solar - burns carbon, oxygen, ... to iron
- (*) no energy from iron burning - collapse - supernova
All matter heavier than carbon has been formed
in the core of a star that exploded as a supernova
- Stellar end states:
- white dwarfs: size of earth, mass of sun, density up to 1
million times that of water
- supported by degenerate electrons, maximum mass = 1.4 solar
- (*) neutron stars: detected as pulsars, mass of 1.4 solar
but size of Ames, neutron degeneracy
- (*) interacting binary stars
- (*) black holes: so dense that escape velocity greater than
speed of light
- The Interstellar Medium
- interstellar absorption lines
- atomic emission line clouds (HII regions, planetary
nebulae, neutral hydrogen)
- interstellar molecules and dust
- The Milky Way
- basic dimensions and structure: ping-pong ball in CD,
100,000 light years across
- rotation: fast rotation in outer parts indicates there must
be a dark massive halo
- spiral arms - spiral density wave
- the Milky Way neighborhood - nearby galaxies like Andromeda,
Magell. clouds
- Galaxy Types: spirals; barred spirals: ellipticals
- Galaxy Distances - the distance pyramid; more reliable close
by, less reliable farther away
- Cepheid variable stars: period-luminosity relation
- internal velocity dispersion correlation to luminosity
(Tully-Fisher)
- average galaxy characteristics
- (*) the Hubble Law
- velocity of recession (through Doppler) proportional to
distance
- the Hubble constant: H, in range from 50 to 100 km/s per
million parsecs
- the expanding universe: all galaxies move away from each
other
- no center for expansion, not an explosion
- (*) Freaky Galaxies
- Quasars - point-like objects with huge red Doppler shifts -
large distances
- rapidly varying brightness - small
- high luminosity
- huge structures visible at radio wavelengths
- Active galaxies (Seyferts, BL Lac objects, radio galaxies)
- supermassive black hole as energy source
- (*) Clusters and superclusters
- galaxies cluster on the megaparsec scale
- clusters also show larger scale organization: the great
wall
- (*) Cosmology - a big, expanding, and structured universe
- age = 10 to 20 billion years
- expansion now implies a Big Bang in past
- Big Bang - produced H, He, and lithium from initial pure
energy fireball
- tests - pervasive 3 K background radiation - observed by
COBE
- problems: uniformity over all space - how to form structure
of supercluster scales?
- seeds of galaxy formation discovered by COBE
- Open vs. Closed universe: the critical density; tests;
current guess is open
- inflation - rapid early expansion leaving us with density
equal to critical density
- if closed, recycled universe (bang, expand, contract,
crunch, bang, expand, ...
- (*) Search for Extraterrestrial Intelligence
- The Drake Equation: probability of other civilizations in
space