Term
| Star A appears brighter than Star B, as seen from Earth. Therefore, Star A must be closer to Earth than Star B. |
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| A Star of apparent magnitude +5 looks brighter than one of apparent magnitude +2 |
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| Red giants are very bright because they are extremely hot. |
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| The radius of a star can be determined if the star's distance and luminosity are known. |
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| Astronomers can distingished between main-sequence and giant stars by purely spectroscopic means |
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| In a spectroscopic binary, the orbital motion of the component stars appears as variations in the overall apparent brightness of the system |
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| IT is possible to have a 1-billion year old O-type main sequence star |
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| Interstellar matter is quite evenly distributed throughout the milky way galaxy |
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| Emission nebulae radiate mainly in the ultraviolet part of the electromagnetic spectrum |
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| Twenty-one-cm radiation can be used to probe the interiors of molecular clouds |
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| The most massive stars form most rapidly |
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| Brown dawrfs take a long time to form, but will eventually become visible as stars on the lower main sequence. |
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| The formation of the first high-mass stars in a collapsing cloud tends to inhibit futher star formation within the cloud |
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| Most stars form as members of groups or clusters |
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| All of the single red-dwarf stars that ever formed are still on the main sequence today |
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| The sun will get brighter as it begins to run out of fuel in its core |
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| A planetary nebula is the disk of matter around a star that will eventually form a planetary system |
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| The various stages of stellar evolution predicted by thoery can be tested by observations of stars in clusters. |
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| A nova is a sudden outburst of light coming from an old main sequence star |
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| IT takes less and less time to fuse heavier and heavier elements inside a high mass star |
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| In a core-collapse supernova, the outer part of the corse rebounds from the inner, high-density core, destorying the entire outer part of the star |
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| Because of stellar nucleosyhthesis, the spectra of old stars show more heavy elements than those of young stars. |
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| Newly formed neutrons stars have extremely strong magnetic fields |
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| All millisecond pulsars are how, or once were, members of binary star systems |
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| The fact that gamma-ray burts are so distant means that they must be very energetic events |
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Definition
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| All things, except light, are attracted by gravity |
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Definition
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| According to general relitivity, space is warped, ot curved, by matter |
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| Although visible light cannot escape from a black hole, high energy radiation, like gamma rays can |
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| Thousands of black holes have now been identified in out galaxy |
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| Herschel's attempt to map the milky way by counting stars led to an inaccurate estimate of the galaxy's size because he was unaware of absorption by interstellar dust |
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| Cepheid variables can be used to determine the distances to the nearest galaxies |
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| Globular clusters trace out the large-scale structure of the Galactic disk |
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| The Galactic halo contains about as much gas and dust as the Galactic disk |
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| The Galactic disk contains only old stars |
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Definition
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| Stars and gas in the galactic disk move in roughly cicrcular orbits around the Galactic Center |
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Definition
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| Astronomers use 21-cm radiation to study Galactic molecular clouds |
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| The most likely explanation of the high-speed motion of stars and gas near the Galactic Center is that they are orbiting a super massive black hole |
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| Most galaxies are spirals like the milky way |
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| Most elliptical galaxies contain only old stars |
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| Irregular galaxies, although small, often have lots of star formation taking place in them |
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| Type I supernovae can be used to determine distances to galaxies |
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| Most galaxies are receeding from the milky way galaxy |
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| Hubble's law can be used to determine distances to the farthest objects in the universe |
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| Active galaxies can emit thousands than our own galaxy. |
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| Intergalactic gas in galaxy clusters emit large amounts of energy in the form of radio waves |
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| Distant galaxies appear to be much larger than those nearby |
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| Galaxy collisons are rare, and have little or no effect on the stars and interstellar gas in the galaxies involved |
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Definition
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| The quasar stage of a galaxy ends because the central black hole swallows up all the matter arounds it. |
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Definition
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| Elliptical galaxies may be formed by mergers between spiral systems. |
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| The fact that a typical quasar would consume an entire galaxy's worth of mass in 10 billion years suggest that quasar lifetimes are relatively long |
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Definition
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| On the largest scales, galaxies in the universe appear to be arranged on huge sheets surrounding nearly empty voids. |
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| The image of a distant quasar can be split into several images by the gravitational field of a foreground cluster along the line of sight |
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