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39 Cards in this Set
- Front
- Back
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Scales in astronomy
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The moon is 30 earth diameters away
The average distance from the sun to the earth is defined to be 1 astronomical unit or 1 AU 1 AU is alos about 8 light minutes light minute is a unite of distance not time earth is 100 solar diameters away from the sun the closest star to the sun is about 20 million solar diameters away from the sun (4.2 light years away) radius of the disk of galaxy is about 75,000 LY |
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celestial equator
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the band of sky that is directly overhead from earths equator
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zenith
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point directly overhead
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what changes light
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acceleration of charged particles
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flux
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flux, where flux is the energy emitted per unit area per unit time
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luminosity
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Luminosity is just the flux times the surface area
def a measure of the radiant power emitted by a star |
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Doppler Effect
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The Doppler formula can then tell us that the star is moving away from us, and the amount of the wavelength shifts tells us the recessional velocity (or "redshift"). If the lines are shifted to shorter wavelengths, then the object is approaching us (it has a "blueshift").
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Hot Stars to cool stars:
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Oh
Be A Fine Girl Kiss Me |
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chemical composition of most stars
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75% hydrogen by mass
23% Helium by mass 2% everything else by mass |
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Absolute magnitude
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The Absolute Magnitude of a star is defined as a matter of convenience to be the magnitude the star would be if it were at a distance of 10 pc. Thus the Sun, with an apparent magnitude of -26.5, has an absolute magnitude of
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THE HERTZSPRUNG-RUSSELL DIAGRAM
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independently made plots of the luminosity and spectral type of nearby stars
The stars do not lie randomly but in a sequence or patern |
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THE HERTZSPRUNG-RUSSELL DIAGRAM cont.
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Most stars lie along the Main Sequence running from hot, luminous stars to cool, faint stars.
There are also Red Giant stars, that are luminous and cool There are Supergiant stars that are very luminous, and have a wide range of temperatures And there are White Dwarf stars that are hot, but very faint. |
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Spectroscopic Binaries
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systems in which the angular seperation between the two stars is too small to see them as seperate stars
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cosmological principle
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the idea that matter in the universe is evenly distributed without a center or edge
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longer wavelength
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low energy
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shorter wavelength
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higher energy
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thermal pressure
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supports star against collapse
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interstellar medium
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contains gas and dust and is what separates the stars
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cepheid variables
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class of variable star that turns out to be of profound importance for the study of other galaxies
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spiral arms
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lanes of interstellar gas, dust, and young stars that wind outward in a plane from the central regions of a galaxy
natural consequence of introducing structure into a differentially rotating fluid. (adding creamer to coffee) |
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disk rotation
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collection of stars and gas, all orbiting in the same direction about the galactic center, it moves differentially unlike solid body masses
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DarkMatter problem: Ideas:
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it could be neutrinos
Massive compact halo objects (MACHOS) weakly interacting massive particles (WIMPs) |
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lookback time
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difference between the current age of the universe and the age of the universe when the light left the object
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cosmological redshift
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the expansion of the universe stretches out all the photons within it, shifting them to longer, redder wavelengths
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Tulley Fisher relation
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the faster a spiral galaxy's rotations speed, the more luminous it is
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radar ranging
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measure the earth sun distance by bouncing radio waves off planets and using some geometry
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parallax
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measure distances to nearby stars by observing how their positions change, relative to the background stars, as earth orbits the sun.
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main sequence fitting
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we know the distance to hyade star cluster in the milky way, so by comparing the apparent brightness of its main sequence stars to those of main sequence stars in other clusters, gives us the distance to the other clusters in our galaxy
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cepheid variables
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when we find a cepheid in a more distant star cluster or galaxy we can determine its luminosity by measuring the period between its peaks in brightness and then use this luminosity to determine the distance
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distant standards
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using cepheids to determine the distances of nearby galaxies we learn the luminosity of white dwarf supernovae and other standard candles enabling us to measure great distances throughout the universe
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hubbles law
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more distant galaxies are moving away from us faster
v=Ho x d Ho =hubbles constant |
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cosmology
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study of the overall structure and evolution of the universe
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spiral galaxies
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prominent disks and spiral arms
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elliptical galaxies
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rounder and redder than spiral galaxies and contain less cool gas and dust
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irregular galaxies
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neither dislike nor rounded
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Galaxy Formation
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1. Hydrogen and Helium gas filled all of space uniformly when the universe was very young
2. The universe was not uniform rather some areas were denser than others |
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Curtis Shapley Debate
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-shapley argued the sun was not at the center of universe
-curtis argued that spiral nebulae were in fact external galaxies -einsteins relativity supposed that universe was expanding and there was no unique center -both wrong about interstellar absorption and starlight is not important in determining the size of the universe -paved way for future discoveries |
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Shapleys Argument
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Correct: in saying the sun was well off from the center, wrong about spiral nebulae and size of the galaxy
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Curtis' Argument
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Right about spiral nebulae being external galaxies, wrong about suns placement and the size of our galaxy
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