Term
| What do we need to measure in order to determine a star's luminosity? |
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Definition
| apparent brightness and distance |
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Term
| If the distance between us and a star is doubled, with everything else remaining the same, the luminosity... |
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Definition
| remains the same, but the apparent brightness is decreased by a factor of four. |
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Term
| How would the apparent brightness of Alpha Centauri change if it were three times farther away? |
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Definition
| It would be only 1/9 as bright. |
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Term
| What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system? |
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Definition
| the time between eclipses and the average distance between the stars |
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Term
| Why is a star's birth mass its most fundamental property? |
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Definition
| A star's birth mass determines its quantity of hydrogen fuel, its central pressure and temperature, and therefore its luminosity. These in turn set the star's main-sequence lifetime and surface temperature. These relationships mean that the birth mass of the star sets most of its other properties. |
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Term
| Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________. |
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Definition
| less luminous, cooler, smaller, and less massive |
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Term
| Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________. |
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Definition
| cooler and larger in radius |
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Term
| Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________. |
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Definition
| hotter and smaller in radius |
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Term
| Approximately, what basic composition are all stars born with? |
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Definition
| three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements |
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Term
| The spectral sequence in order of decreasing temperature is |
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Definition
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Term
| Why is the spectral sequence of stars not alphabetical? |
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Definition
| The original alphabetical labeling did not correspond to surface temperature and thus had to be reordered |
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Term
| Suppose you see two main-sequence stars of the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude? (Neglect any effects that might be caused by interstellar dust and gas.) |
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Definition
| Star 1 is 10 times more distant than Star 2. |
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Term
| On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous? |
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Definition
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Term
| In order to understand star clusters, we need to be able to estimate their ages. What technique do scientists use for this? |
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Definition
| finding the main-sequence turnoff point of the stars |
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Term
| What prevents a brown dwarf from undergoing nuclear fusion? |
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Definition
| Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion. |
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Term
| Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram? |
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Definition
| surface temperature on the horizontal axis and luminosity on the vertical axis |
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Term
| On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii? |
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Definition
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Term
| You observe a star in the disk of the Milky Way, and you want to plot the star on an H-R diagram. You will need to determine all of the following, except the |
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Definition
| rotation rate of the star. |
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Term
| how do we determine the luminosity of the Sun from its flux? |
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Definition
| luminosity = flux * area of sphere at your distance |
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Term
| what allows us to measure the distance for nearby stars? |
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Definition
parallax, sin p = 1 AU / d
where p will be either in radians or degrees |
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Term
| hot stars should appear... |
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Definition
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Term
| how does one determine the masses of stars in binary systems? |
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Definition
| Newton's form of Kepler's 3rd Law |
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Term
| where a star lies on the main sequence is a function of.... |
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Definition
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Term
| when a star's mass increases... |
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Definition
| its gravity increases and its thermal energy increases to keep the star from collapsing |
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Term
| when thermal pressure increases... |
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Definition
| temperature and density in the core increase, leading to an increase in the rate of fusion |
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