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35 Cards in this Set
- Front
- Back
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What are the three major types of galaxies? |
Hubble ultra deep field shows elliptical galaxy irregular galaxies and spiral galaxies |
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Elliptical galaxy |
All spherical component, virtually no disk component. its red yellow color indicates an older star population
often found in huge clusters of galaxies up to hundreds of thousands |
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Irregular galaxy |
it's blue-white color indicates ongoing star formation more common in huge clusters of galaxies up to hundreds of thousands |
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Spiral galaxies |
often found in groups of a few dozen galaxies |
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How do you measure galactic distances? or distances between galaxies? |
We use the cosmic distance ladder. |
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Sizing up the solar system historically? |
paralax angle gives distance d=au-a(planet) keplars third law (pplanet/year)ttp2=(aplanet/au)ttp3) |
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first step in the cosmic distance ladder what is radar ranging? |
determine size of the solar system using radar which calculates the radii of plaetary orbits aroudn the sun. |
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Step two |
determines the distance of stars out to about 1000 light years using stellar parllax. The baseline to this is determined in teh first step. |
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Hipparcos Satellite |
determined the positions of more than 10000 stars with very high precision opporating from 1989 to 1993 |
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The Gia Satellite |
launched in 2013 measure the positions of about 1 billion stars with unprecedented precision and be finished by 2019 |
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sTEP THREE |
REQUIRE THE REATION BETWEEN LUMINOSITY AND APPARENT BRIGHTNESS. BRIGHTNESS IS EQUAL TO LUMINOSITY DIVIDED BY AREA.
AREA is determined by 4pi times distance to the power of 2 |
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How can we determine a stars distance? |
by knowing its luminosity and apparent brightness.
distance is the square root of the luminosity divided by 4pi times brightness |
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what are the two basic aplications for the relation of brightnes, luminosity and distance. |
i don't know. **** this math. |
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What is the dual role of the brightness distance luminosity relation? |
if you konw brightness and distance you can find luminosity if you know luminosity and brightness you can find distance |
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Step three main sequence fitting |
the apparent brightness of a stars main sequence on the HR scape tells us its distance. works up to about 100000 light years.
brightness added to luminosity yields distance to the stars. |
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What is step four? what do we need to know? |
knowing a star clusters distance, we can determine the luminosity of each type of star within it. |
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Who is Henrietta swan leavitt? |
in 1908 she discovered bright variable stars with the remarkable property that their luminosity is directly correlated with the oscillation period of thier apparent brightness.
i.e. luminosity is about period ttp 1.2 |
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Which stars are very luminous? |
cepheid variable stars are very luminous. polaris at a distance of about 430 light years is the closest cepheid star.
We can use cepheid stars as standard candles because of the pulsing brightness which tells us its luminosity. |
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how do the measurements relate to eachother? |
period tells us lumionsity. luminosity and brightness tell us distance. works up to 100 000 000 light years. |
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explanation for the periodic variation in luminosity of some stars |
multiple shell burning in the final life cycles of a very massive star muclear fusion heats the star and expands it becomes brighter due to increase in radiating surface but expansion also cools star and reduces nuclear fusion rates. makes star shrink again, becoming dimmer due to decrease f radiating surface, but also becomes hotter again due to increase in nuclear fusion rates causing the star to reexpand |
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maser |
microwave amplification by stimulated emission of radiation. Reinforces the 4th rung. |
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Example of a 3 level maser. what are the three steps? |
pumping through collisions fast transition into level two also through collisions or radiation stimulated emission a photon with energy can stimulate emission of a second identical photon. and can trigger an avalanche of identical photons. |
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maser blue shifts and red shifts |
may tell us how fast the galaxy moves v but also how fast the accretion disk moves. |
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how can entire galaxis be used as standard candles |
luminosity is related to rotation speed. this method can be used up to 600000000 light years. |
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5th rung of the ladder white dwarf supernovae |
remnant cores of dead stars with core masses below 1.4 solar masses. fusion in their cores stopped becasue their hydrogen and helium supplies are exhausted but degeneracy pressure of electrons prevents them from further collapse. glow because still hot but evetually will become black dwarfs if not in a bionary unit. |
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Typical supernova light curves |
Massive star supernova have variations while white dwarf supernovae always follow essentially teh same light curve with a peak of luminosity about 10 billion times the luminosity of the sun. |
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what are the standard candles at each rung? |
3rd rung are star clusters 4th run cepheid variable stars and dully fisher disk galaxies fifth rung white dwarf supernovae |
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How do we measure galaxy distance? |
using a chain of independent techniques at every rung of the ladder. radar parallax main sequence fitting cepheids distant standards |
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what are three properties of measuring distance? |
chain begins with parallax measurements that build on radar ranging in our solar system using parallax and the relationship between luminosity, distance and brightness we can calibrate a series of standard candles we can measure distances greater than 10 billion light years using white dwarf supernovae as standard candles. |
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Spiral Nebulae |
debate of whether spiral nebulae were entire galaxies or smaller collections of stars within the milky way
hubble settled this by measuring the distance to andromeda |
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How did hubble measure andromeda's distance? |
he used cepheid variables as standard candles the specrtal features of virtually all galaxies are redshifted, which means that they're moving away from us. by measuring distances to galaxies hubble found that reshift and distance are related in a special way
Velocity= H0X DISTANCE |
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HUBBLES EQUATION |
VELOXITY=H0 TIMES DISTANCE DISTANCE = VELOCITY/H0 distances from the farthest galaxies are measured by their red shifts |
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what is the cosmological principle? |
matter is evenly distributed on a very large scales in teh universe no center or boundries cosmological principle has not been proven beyond doubt but is consistent with all observations to date. |
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how does hubble tell us the age of the universe? |
hubbles content tells us the age of the universe because it relates to the velocities and distances of all galaxies.
age= distance divided by velocity |
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how does the universe' expansion effect measurements of distances? |
distances between faraway galaxies change while light travels astronomers think in terms of look back time rather than distance
cosmological redshift is directly related to lookback time. the faster a galaxy is moving away from us the greater its distance is. |
