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Scales of the Universe
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Size of solar system
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Definition of the light year
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The nearest: star, galaxy
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The composition and age of the Universe
Gravity: Newton's Laws
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Gravity as a fundamental force: Central, Universal, and Cosmic
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Other Cosmic forces: Electromagnetic force, Weak Nuclear force, strong
nuclear force
Light: a form of energy=electromagnetic radiation
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wave nature: wavelength (l) x frequency (f) = speed (c for light)
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different wavelength = different 'color'
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particle nature: photon as a bundle of light energy; energy proportional to
frequency
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Brightness proportional to luminosity divided by distance squared
Electromagnetic spectrum
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short wavelength (gamma ray) to long wavelength (radio)
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high energy (gamma ray) to low energy (radio)
Thermal (blackbody) radiation - radiation from objects because they are hot
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Wien's law: wavelength of maximum emission increases with decreasing
temperature
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Stefan-Boltzmann Law: energy emitted proportional to T4
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stars are like blackbodies; hot stars are blue, cool stars are red
Spectral Lines
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Kirchoff's laws: emission, absorption, and continuous spectra
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discrete atomic energy levels correspond to discrete electron orbits
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transitions up in energy absorb photons; transitions down emit photons
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bigger energy difference between levels, higher energy photon involved
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each element has its own signature spectral lines; atomic fingerprints
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Spectroscopy as the "Rosetta Stone" in astronomy
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Telescopes:
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light gathering power depends on size2
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resolution depend on size / wavelength
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mechanical and optical specifications
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instrumentation: photometry, spectroscopy, imaging
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advantages and disadvantages of astronomy from space
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adaptive optics
o Atmospheric
transmission : optical, radio transparent, infrared : partially
opaque, UV opaque, X-ray through γ-ray opaque
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The Sun
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surface features: sunspots, prominences, corona, etc.
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energy transport by radiation, conduction and convection
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energy production by nuclear fusion: E=mc2; 4 hydrogen -> 1 helium + energy
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solar neutrino problem
Stars
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stellar spectra: hot to cool (=blue to red): O,B,A,F,G,K,M
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distances via trigonometric parallax
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radial velocity: the Doppler effect
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change in wavelength (Δ λ) divided by wavelength (λ) = velocity in line-ofsight / c
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ranges of luminosity and temperature
The HR Diagram
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2-D classification scheme: luminosity versus temperature (or color)
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main sequence, red giants, white dwarfs
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stellar mass via binary stars
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the main sequence: higher mass = more luminous = bluer = rarer
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main sequence life time = 10 billion years divided by mass3
Star Clusters: key objects for stellar evolution
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associations, open clusters, globular clusters
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stars become red giants when hydrogen exhausted in core
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main sequence peeled down with age
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oldest clusters are 12-14 billion years old
Stellar evolution
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star formation in molecular clouds; triggers, protostellar collapse, nuclear
ignition
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main sequence - longest stage
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core H exhaustion - become red giants
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helium ignition - helium flash if mass less than twice sun
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core helium exhaustion: giant branch again
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M < 8 solar - white dwarf exposure and planetary nebula formation
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M > 8 solar - burns carbon, oxygen, ... to iron
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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
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Stellar end states:
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white dwarfs: size of earth, mass of sun, density up to 1 million times that of
water
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supported by degenerate electrons, maximum mass = 1.4 solar
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neutron stars: detected as pulsars, mass of 1.4 solar but size of Ames, neutron
degeneracy
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black holes: so dense that escape velocity greater than speed of light
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detecting black holes - massive binaries and X-ray emission
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gamma-ray bursts as sites of black hole production via hypernovae
The Milky Way
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the interstellar medium
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basic dimensions and structure: ping-pong ball in CD, 100,000 light years
across
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rotation: fast rotation in outer parts indicates there must be a dark massive halo
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spiral arms - spiral density wave
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The Milky Way neighborhood - nearby galaxies like Andromeda, Magellan clouds
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Galaxy Types: spirals; barred spirals: ellipticals
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Galaxy Distances - the distance pyramid; more reliable close by, less reliable farther
away
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Cepheid variable stars: period-luminosity relation
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internal velocity dispersion correlation to luminosity (Tully-Fisher)
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Type Ia Supernovae, average galaxy characteristics
The Hubble Law
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velocity of recession (through Doppler) proportional to distance
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the Hubble constant: H, in range from 50 to 100 km/s per million parsecs best current value is 74
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the expanding universe: all galaxies move away from each other
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no center for expansion, not an explosion
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Freaky Galaxies
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Quasars - point-like objects with huge red Doppler shifts - large distances
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rapidly varying brightness - small
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high luminosity
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huge structures visible at radio wavelengths
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Active galaxies (Seyferts, BL Lac objects, radio galaxies)
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supermassive black hole as energy source
Clusters and superclusters
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galaxies cluster on the megaparsec scale
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clusters also show larger scale organization: the great wall
Cosmology - a big, expanding, and structured universe
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age = 10 to 20 billion years (best guess: 13 billion)
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expansion now implies a Big Bang in past
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Big Bang - produced H, He, and lithium from initial pure energy fireball
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tests - pervasive 3 K background radiation - observed by COBE
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seeds of galaxy formation discovered by COBE
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Open vs. Closed universe: the critical density; tests; current guess is open
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inflation - rapid early expansion leaving us with density equal to critical
density
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the accelerating universe - Type Ia supernova results
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Imaging the first galaxies: the Hubble Deep Field and Ultra Deep Field
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if closed, recycled universe (bang, expand, contract, crunch, bang, expand, ...