Problem Set 1 Solution

# Problem Set 1 Solution - Astronomy 201 Problem Set 1...

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Astronomy 201 Problem Set 1 Assigned: 30 Aug 2004 Due: 13 Sep 2004 Remember: No late homework and homework counts 40% of the total grade. Each question / problem is of equal weight and equals 5 points. Chapter 1: Review and Discussion – 1, 7, 9, 10, 14 Problems: 1, 3, 4, 9, 10 Review and Discussion 1. Compare the size of Earth with that of the Sun, the Milky Way Galaxy, and the entire universe. As given in Appendix 1, the Sun is about 100 times the size of the Earth. From Section 1.1, a light year is about 10 13 km and a typical galaxy is about 100,000 Ly in diameter, or 10 18 km. This makes a galaxy about 10 14 times larger than Earth. Astronomers can see objects as distant as 10 billion Ly or 10 23 km which is 10 5 times the size of a galaxy or 10 19 times the size of the Earth. 7. How and why does a day measured by the Sun differ from a day measured with respect to the stars? The true rotation of the Earth is measured with respect to the stars, the sidereal day. But during that interval of time, the Earth has moved in its orbit around the Sun (by about 1 degree). In order for the Sun to appear in the same location as it did on the previous day, the Earth must rotate slightly more. The solar day is therefore slightly longer than the sidereal day. Refer also to Figure 1.13. 9. Why do we see different stars at different times of the year? Due to the yearly motion of the Earth around the Sun, in the summer the Earth points in a direction 180° opposite of the direction it points during the winter. To see this think of yourself standing looking at the sky at midnight: Your back is to the Sun no matter the time of the year but as the Earth travels you are facing in different directions. 10. Why are there seasons on Earth? The seasons of the Earth are caused by the tilt of the Earth's equator relative to its orbit around the Sun. This results in the Sun appearing higher in the sky during spring and summer months and causes higher rates of heating. In the fall and winter months the Sun appears much lower in the sky, its light falling more at an angle to the Earth's surface, and heats it less. 14. What causes a lunar eclipse? A solar eclipse? A lunar eclipse is caused by the Moon entering the shadow of the Earth. A solar eclipse is caused by the Earth entering the shadow of the Moon. Problems :

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1. In one second, light leaving Los Angeles reaches approximately as far as (a) San Francisco, about 500 km; (b) London, roughly 10,000 km; (c) the Moon, 384,000 km; (d) Venus, 45,000,000 km from Earth at closest approach; or (e) the nearest star, about four light-years from Earth. Which is correct?
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## This note was uploaded on 11/01/2009 for the course PHYS 229 taught by Professor Mehmetyali during the Fall '09 term at Sabancı University.

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Problem Set 1 Solution - Astronomy 201 Problem Set 1...

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