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Exam 17: Analyzing Starlight

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Question 1

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Why are astronomers much more interested in the luminosity of a star than its apparent brightness?

A) because luminosity can be measured exactly, but apparent brightness can only be roughly estimated
B) because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth
C) because the luminosity also tells us what elements the star is made of, while apparent brightness cannot tell us a star's chemical make-up
D) because luminosity can tell us how bright it is inside the star's core, while apparent brightness only tells us about its outside layers
E) you can't fool me, there is no difference between luminosity and apparent brightness; they are merely different terms for the same property of a star
Section 17.2: Colors of Stars

F) A) and D)
G) None of the above

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Question 2

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When an astronomer measures a color index for a star, what is she measuring?

A) what color the human eye sees when people look at that star
B) the difference between how bright a star looks at two different wavelength regions
C) the total luminosity of the star in all parts of the electromagnetic spectrum
D) the amount of hydrogen in the atmosphere of the star
E) how the color of the star is changed when its light passes through the Earth's atmosphere
Section 17.3: The Spectra of Stars (and Brown Dwarfs)

F) C) and D)
G) B) and E)

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Question 3

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Two stars have the exact same luminosity, but star Y is four times dimmer looking that star X. This means that

Starting in 2009, astronomers have been discovering really cool objects out there (cool here meaning low-temperature, as well as really interesting) , which they have called Y dwarfs. What distinguishes these brown dwarfs from others that astronomers have discovered?

One key difference that astronomers use to distinguish between brown dwarfs and high-mass planets is that:

A team of astronomers takes spectra of thousands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that the stars

Using a good pair of binoculars, you observe a section of the sky where there are stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it is:

A graduate student has done a careful analysis of the spectrum of a star. While she has found lines from many elements, there was not a trace of the element helium in the spectra she has been analyzing. From this she can now conclude:

One similarity in the spectra of T dwarf stars and giant planets in our solar system is that their spectra show:

The astronomer who, at the turn of the century, measured the spectra of hundreds of thousands of stars, leaving a catalog that astronomers used for the rest of the century, was:

Which color star is likely to be the hottest?

After a lot of work, a group of graduate students has finally measured the wavelengths of many dozens of lines in the spectrum of a distant star. If a number of the lines come from molecules such as titanium oxide, the star is likely to be which spectral type:

Astronomers call the motion of a star across the sky (perpendicular to our line of sight) its

An astronomer whose secret hobby is riding merry-go-rounds has dedicated his career to finding the stars that rotate the most rapidly. But the stars are all very far away, so none of them can be seen to spin even when he looks through the largest telescopes. How then can he identify the stars that rotate rapidly?

Studies of the spectra of stars have revealed that the element that makes up the majority of the stars (75% by mass) is

Which of the following looks the brightest in the sky?

Imagine that a brilliant but quirky scientist in the biology department manages to put you in a deep freeze and you wake up in a million years. Which of the following statements about the sky you would see in that future time is correct?

The first astronomer who did photometry in a systematic way (even though he did not have a telescope) was

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:

In recent decades, astronomers discovered stars even cooler than the traditional spectral type M stars recently. Astronomers gave these cool stars a new spectral type, L. If you wanted to go out and find more such type L stars, what kind of instrument would it be smart to use?