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Unformatted text preview: Astronomy C10 : HW 2
Introduction to Astronomy Homework 2 Problems from Pasachoﬀ and Filippenko
1. (11 points) See the course reader.
2. (4 points) If someone were to say that we cannot know the composition of distant stars,
since there is no way to perform experiments on them in terrestrial laboratories, how would
you respond?
3. (4 points) A spectral line from the left side of Saturn’s rings, as you see them, is at a
wavelength slightly shorter than the same spectral line measured fro the right side of
Saturn’s rings. Which way (direction) is Saturn rotating, and why?
4. (4 points) The Earth’s average temperature is about 27◦ C. What is its average temperature
in kelvins? (Requires a numerical answer)
5. (4 points) An iron rod is heated by a welder’s torch. Initially it glows a dull red, then a
brighter orange, and ﬁnally very bright white. Discuss this sequence in terms of blackbody
radiation.
6. (4 points) Does the Doppler eﬀect depend on the distance between the source of light and
the observer? Explain.
7. (2 + 2 = 4 points) (a) If one photon has 10 times the frequency of another photon, which
photon is the more energetic, and by what factor? (b) Answer the same question for the
case where the ﬁrst photon has twice the wavelength of the second photon. (Requires a
numerical answer)
8. (4 points) Consider a black body whose temperature is 3 K. At what wavelength does
its spectrum peak? (We will see the importance of this radiation in the discussion of
cosmology in Chapter 19). (Requires a numerical answer)
9. (4 points) How many times hotter than the Sun’s surface is the surface of a star the same
size, but that gives oﬀ twice the Sun’s energy per second (that is, is twice as luminous)?
10. (7 points total) See the course reader. 1 ...
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This note was uploaded on 09/18/2010 for the course ASTRON 05989 taught by Professor Filippenko during the Fall '10 term at University of California, Berkeley.
 Fall '10
 FILIPPENKO

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