Homework 4

# Homework 4 - Danielle Kim Homework 4 3 Draw a diagram of...

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Danielle Kim Homework 4 3. Draw a diagram of our galaxy as seen from the side, and show the approximate location of the Sun. Show the sizes of all relevant features, in particular show: the diameter and thickness of the disk, the size of the central bulge, the distance from the center of the galaxy to the Sun. What is the approximate mass (in terms of solar mass) and total luminosity (in terms of solar luminosity) of our galaxy? Total mass – 9 x 10 10 solar masses Total luminosity - 10 44 erg/s 4. (a) How would the Milky Way appear if we were near a star located close to the edge of the Galaxy? (b) How did interstellar extinction mislead astronomers into believing that we are near the center of the galaxy? (a) We would see a large, flat disk of stars, dust and gas with a dense central ball of stars. Above and below the plane of the Milky Way we would see globular clusters whose distribution is centered about the center of the galaxy. We can't clearly see the galactic center from our location because the interstellar dust clouds between us and the galactic nucleus reduce the amount of light that reaches us from the nucleus. (b) In 1785, the musician turned astronomer, William Herschel pioneered the technique of star counts in an attempt to deduce the structure of the Milky Way. Herschel pointed his telescope in various directions in the sky and counted the number of stars he could see in a standard size field

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of view. If he saw more stars in a given direction, Herschel assumed that the Milky Way extended farther in that direction. Herschel correctly concluded that the Milky Way was a disk
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