astronomy exam 2
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97 terms
Terms | Definitions |
|---|---|
 an "open" universe is | one that will expand forever |
| a universe is | at the critical density between open and closed |
| what came before the big bang is | a vexing philosophical question for science, as for religion and other disciplines of thought |
| we will eventually be able to locate where the big bang occurred | none of the above |
| how does the average density of the universe affect its predicted fate? | if the universe has a high density its expansion is expected to reverse and it will collapse |
| the cosmic background was discovered | as a faint noise component in the microwave spectral region |
| one of the reasons the sky is dark at night is | the universe is expanding |
| if new measurements showed that the currently adopted value if hubbles constant is two times too small then we could conclude that the age of the universe | was half what we had believed before |
| the assumption that the universe is homogeneous on very large scales is | the cosmological principle |
| hubbles law implies that | the universe is expanding |
| to a physicist studying the early universe, unification is | the concept that the fundamental forces of physics unified under extreme conditions |
| the period of very rapid inflation in the early universe solves the mystery of | why the universe is so uniform |
| understanding how subatomic particles like quarks behave is critical to understanding | conditions in the early universe |
| the "flatness problem" refers to | how the universe came out just at the density that balances its gravity |
| you are made of | baryonic matter |
| we know that the universe is only about 6% protons and neutrons - baryons - because | fusion reactions would have produced more lithium and maybe heavier elements if there had been more baryons |
| the 3 degree cosmic background radiation originated when | electrons were captured by protons to make the universe transparent |
| the contrast in the structure on the 3K cosmic background tells us about | what kind of matter formed (fraction of baryonic or nonbaryonic) |
| dark matter | played a critical role in the merger of galaxies in the early universe |
| the early stages of development of the universe | are surprisingly well understood through a combination of physics and astronomy |
| the cosmic background radiation provides strong enough evidence that | the universe evolved from a hot, dense state |
| the cosmic background radiation is visible equally in every direction because | we are looking back to when the universe was young and opaque in every direction |
| astronomers cannot look back further than when the universe was 300,000 to 500,0000 years because | the universe was made of dense ionized gas that was opaque to light |
| the granules visible on the suns surface are evidence of | convection |
| the suns corona has a temperature of more than a million degrees. What wavelength regime would be most useful for studying the corona? | x-rays |
| the term "solar cycle" refers to | the 22 year pattern in sunspots and magnetic field direction |
| the major constituents of the sun are | hydrogen and helium |
| the danger to astronauts from solar flares and coronal mass ejection is greatest when | sun is at a sunspot maximum |
| the underlying cause of the solar cycle is | winding up of the suns magnetic field due to differential rotation |
| sunspots are | regions where a strong magnetic dipole interferes with the outward transport of energy |
| the sun has been able to produce energy for billions of years by | nuclear fusion |
| the suns output is so stable because | pressure of suns gas just balances gravitational contraction |
| although deep inside the sun, energy is carried by photon streaming, energy is carried to the surface of the sun | by convection, like boiling |
| if we have a container of hydrogen gas sitting in a laboratory on earth, why doesnt it turn into helium? | because the temperature and pressure are too low |
| hydrogen fusion can produce energy because | the fusion products weigh a little less than the input materials, and the mass that is lost appears as energy |
| if the earth were further from the sun than it actually is, the parallax angle for stars would be | larger |
| which two things are needed to determine an objects distance from the earth if it is too distant to use trigonometric parallaxes | apparent brightness and luminosity |
| two stars, X and Y, have the same luminosity but star X is a very blue star while Y is a red star. Which star has the larger radius? | Star Y |
| you are living 200 years ago and want to discover parallax. Your best bet is to choose | stars with large proper motions |
| the sequence of spectral types that miss cannon discovered is actually a sequence | of temperatures |
| if you want to measure the mass of a star you must | look for a pair of stars orbiting each other & use keplers 3rd law |
| to measure the luminosity of the sun from the earth, we need to measure | earths distance from the sun & the flux earth receives from the sun (apparent brightness of the sun at the earth) |
| the basic properties that control the current status of a star are | age, mass, initial composition |
| a star will become a red giant when | it can no longer convert H to He in its core |
| a star may be a variable star because | it alternately expands and contracts |
| the oldest stars are most likely to be | the least massive stars |
| the lower limit on the size of a star is set by | the mass require to get the core hot enough for conversion of H to He |
| two stars both have spectral type A. One has a luminosity that is 1000 times larger than the other. What parameter differs the most between these two stars? | radius |
| the upper limit on the size of a star is set by | the stability against photon pressure |
| stars in order of increasing mass | Barnards (T=3370), Sun (T=5800), Spica (T=26,000) |
| under what circumstances can a star convert oxygen to silicon | when the core of a massive star gets hot enough |
| a white dwarf does not collapse further because | its electrons cant be squeezed together any more |
| pulsars vary their light output by | sweeping a light beam across our line of sight |
| planetary nebulae are | the ejected outer layers of a dying star |
| a neutron star is mostly neutrons because | the huge pressure has caused its electrons to merge with its protons to make neutrons |
| if you add mass to a white dwarf to "bulk it up" above 1.4 solar masses, | it will get smaller and smaller and finally collapse into a neutron star |
| the most important aspect (to us) of the material ejected by dying stars is | we are made of material ejected by dying stars a long time ago |
| what is the closest location for finding material formed in a supernova explosion | your own body |
| a remarkable observation from the 1987A supernova was | the detection of neutrinos |
| we know that the crab nebula is a supernova remnant because | it contains a pulsar, chinese astronomers witnessed the explosion, it emits lots of x-rays, its gas is moving very rapidly |
| the crab nebula pulsar is spinning | fast because it is young |
| the cooling rate in SN 1987A showed that | it contained huge amounts of cobalt |
| if you took spectra of a supernova remnant, you would see | many elements such as O,C, Si |
| the elements like oxygen and iron in the earth got there because | long ago, a supernova made them and ejected them into interstellar space, where they were eventually in the gas cloud that became the sun |
| star A has a parallax of 0.5" while star B has a parallax of 0.15" | star A is closer than star B and star A is 2 parsecs away |
| the "big bang" model of the universe was confirmed when we | detected the 3K light over and redshifted to its very low temperature |
| most of the helium was made | in thermonuclear reactions in the first few minutes of the universe |
| grand unified theories suggest that, at extremely high temperatures and pressure | all the forces of physics can be explained in a single physical law |
| the low luminosity stars on the main sequence | are the coolest |
| the sun will end its life as | none of the above |
| observational proof that neutron stars exist is provided by | pulsars |
| the escape velocity at a black holes event horizon is | the speed of light |
| heavy elements like silver and gold are formed | in supernova explosions |
| stars on the main sequence all | are in hydrostatic equilibrium |
| we know about dark matter | from the rotation curves of galaxies that show mass outside the region of stars |
| why does the rotation curve of a galaxy increase with increasing distance near the galaxys center? | the encircled mass increases so fast that gravity increases with radius |
| what is the evidence there is dark matter beyond the disks of spiral galaxies | the stellar mass distribution does not account for the rotation curve of the galaxies |
| the outer part of the rotation curve of a galaxy is flat; this fact indicates that | where the curve is flat, the encircled mass increases with increasing distance from the center |
| we think that either dark matter is in the form of low mass brown dwarfs and wandering planets, or, more likely | the universe is filled with an undetected type of nuclear particle |
| spiral arms are prominent in some galaxies because | they show where young and bright stars have formed |
| the various types of galaxy | include spirals, ellipticals, and irregulars |
| we see where the young stars are in a galaxy most easily when we look in | the ultraviolet and far infrared |
| galaxies are distributed | in vast sheets and filaments that make a structure a little like soap bubbles & in clusters and groups |
| the mass of a cluster of galaxies | includes a significant part from very hot gas and even more from dark matter |
| gravitational lensing | produces peculiar arc-like images of galaxies at high redshift behind massive galaxy clusters |
| the large scale distribution of the galaxies in space is a result of | the structure of the early universe |
| gravitational lenses in galaxy clusters are used | to confirm that the clusters have huge amounts of dark matter |
| the gas in an HI region is comprised of | hydrogen gas with electrons in the ground state |
| the molecular cloud is | a large, cold, dense, collection of interstellar gas and dust |
| a newly formed massive, hot star changes the surrounding interstellar gas into | a glowing cloud of excited gas called an HII region |
| interstellar dust makes the things behind it look | redder and fainter |
| a "reflection nebula" is | an interstellar cloud that is lit up by scattering light toward us from a star near the cloud |
| galaxies come | in a limited number of shapes that we can describe in systematic ways |
| we study galaxies at very high redshift to | determine how galaxies form and evolve to ones like ours |
| in very deep images that let us detect very distant and hence young galaxies, we find them to be | generally to be smaller and with less regular structure compared with nearby ones |
| an HII region can be identified from | its emission lines |
| molecular clouds are mostly composed of | molecular hydrogen |
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