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Approximately, what basic composition are all stars born with? |
three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements |
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Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ? |
mass they are formed with |
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What are the standard units for luminosity? |
watts |
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A star’s luminosity is the |
total amount of light that the star radiates each second. |
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What are the standard units for apparent brightness? |
watts per square meter |
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If the distance between us and a star is doubled, with everything else remaining the same, the luminosity |
remains the same, but the apparent brightness is decreased by a factor of four. |
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Which of the following correctly states the luminosity-distance formula? |
apparent brightness=(luminosity)/[4pi x (distance)^2] |
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Why do astronomers often measure the visible-light apparent brightness instead of the total apparent brightness of a star? |
In order to measure the total apparent brightness of a star, you must measure its brightness in all wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface of Earth are visible and radio wavelengths. |
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Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The distance to this star is |
10 parsecs |
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Suppose that you measure the parallax angle for a particular star to be 0.5 arcsecond. The distance to this star is |
2 parsecs. |
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The most distant stars we can measure stellar parallax for are approximately |
500 parsecs away. |
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Which of the following statements about apparent and absolute magnitudes is true? |
All of the above are true. A) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. B) A star with apparent magnitude 1 is brighter than one with apparent magnitude 2. C) The absolute magnitude of a star is another measure of its luminosity. D) A star’s absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. |
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The spectral sequence sorts stars according to |
surface temperature |
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The spectral sequence in order of decreasing temperature is |
OBAFGKM |
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Why is the spectral sequence of stars not alphabetical? |
The original alphabetical labeling did not correspond to surface temperature and thus had to be reordered. |
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Which of the following statements about spectral types of stars is true? |
All of the above are true A) The spectral type of a star can be used to determine its surface temperature. B) The spectral type of a star can be used to determine its color. C) A star with spectral type A is cooler than a star with spectral type B. D) A star with spectral type F2 is hotter than a star with spectral type F3. |
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Which of the following persons reorganized the spectral classification scheme into the one we use today and personally classified over 400,000 stars? |
Annie Jump Cannon |
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Which of the following persons used the ideas of quantum mechanics to describe why the spectral classification scheme is in order of decreasing temperature? |
Cecilia Payne-Gaposchkin |
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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.) |
Star 1 is 10 times more distant than Star 2. |
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Which of the following terms is given to a pair of stars that appear to change positions in the sky, indicating that they are orbiting one another? |
visual binary |
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Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts? |
spectroscopic binary |
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Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram? |
surface temperature on the horizontal axis and luminosity on the vertical axis |
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On a Hertzsprung-Russell diagram, where would we find stars that are cool and dim? |
lower right |
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On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous? |
upper right |
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On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii? |
upper right |
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On a Hertzsprung-Russell diagram, where on the main sequence would we find stars that have the greatest mass? |
upper left |
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On a Hertzsprung-Russell diagram, where would we find red giant stars? |
upper right |
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On a Hertzsprung-Russell diagram, where would we find white dwarfs? |
lower left |
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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 |
rotation rate of the star. |
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On the main sequence, stars obtain their energy |
by converting hydrogen to helium. |
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The faintest star visible to the naked eye has an apparent visual magnitude of about |
6 |
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Which of the following is the most common type of main-sequence star? |
an M star |
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Which of the following characteristics of stars has the greatest range in values? |
luminosity |
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A star of spectral type O lives approximately how long on the main sequence? |
10 million years |
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A star of spectral type G lives approximately how long on the main sequence? |
10 billion years |
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Which of the following is true about low-mass stars compared to high-mass stars? |
Low-mass stars are cooler and less luminous than high-mass stars. |
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Which of the following luminosity classes refers to stars on the main sequence? |
V |
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In a pulsating variable star, which characteristic of the star changes dramatically with time? |
luminosity |
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Why are Cepheid variables so important for measuring distances in astronomy? |
Their luminosity can be inferred from their period. |
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Which of the following statements about an open cluster is true? |
All stars in the cluster are approximately the same age. |
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Which of the following statements about a globular cluster is true? |
Most stars in the cluster are yellow or reddish in color. |
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Cluster ages can be determined from |
main sequence turnoff. |
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In order to understand star clusters, we need to be able to estimate their ages. What technique do scientists use for this? |
finding the main-sequence turnoff point of the stars |
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