# ps09 - Astronomy 10 Fall 2008 Homework 9 40 points total...

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Unformatted text preview: Astronomy 10, Fall 2008 Homework 9 - 40 points total Due in the boxes in the basement of Campbell Hall by 5pm Tuesday, November 18 . Be sure to include your name, SID, Section Number, and GSI name on your homework, and staple it together. 1. Cosmic Aspect Ratios (5 points) Just how thin a flat disk is can be quantified by its aspect ratio, which is the ratio of its diameter to its height. (a) A standard CD is 12 cm in diameter and 1 . 2 mm thick. What is the aspect ratio for a CD? (2 points) (b) We can approximate the thickness of the solar system’s planetary disk by how far off of the ecliptic the planets stray. This gives a thickness of about 1 AU. (Saturn and Neptune being the largest deviations. Note Pluto is not counted here; it strays more than 12 AU from the ecliptic.) The size can be taken to be the diameter of Neptune’s orbit, 60 AU. What is the aspect ratio for the solar system? (1 point) (c) Astronomers have measured the Milky Way to be about 30 , 000 pc in diameter, and about 300 pc thick. What is the aspect ratio of the Milky Way? Compare to your other answers from parts (a) and (b). (2 points) 2. Star Counting I (7 points) By looking out and counting how many stars we see, we can estimate the total number of stars in the Milky Way. In the early 20th century, astronomers estimated that about 1 billion stars were in the Galaxy. At the time, however, they did not know about the effects of dust blocking stars verythe Galaxy....
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ps09 - Astronomy 10 Fall 2008 Homework 9 40 points total...

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