Homework 7. The Rotation of the Sun

Name: ________________________ Due 10/17 ID Number: ________________________

Here are six images of the Sun taken on six days in September 2005. A very large sunspot can be seen crossing the Sun's disk -- in fact, this spot was so large that it could be seen without a telescope!

Sun on 09/11/05   Sun on 09/12/05   Sun on 09/13/05
Sun on 09/14/05   Sun on 09/15/05   Sun on 09/16/05
1. On the circle at right, plot the position of the sunspot on each successive day. Then, draw a line across the disk indicating the Sun's equator, and show which direction the Sun is rotating.   A circle

2. Now, using the spot positions you plotted in step #1, measure the distance between the spot's position on 09/11/05 and its position on 09/16/05. Divide your result by the diameter of the circle. This gives you the fraction of the Sun's diameter the spot moved between 09/11/05 and 09/16/05.

3. The Sun's circumference C is related to its diameter D by C = Greek letter pi D. Using your result for step #2, what fraction of the Sun's circumference did the spot move?

4. Finally, given that approximately 5 days elapsed between 09/11/05 and 09/16/05, how long would it take the spot to make one complete circle around the Sun and return to its original position? This is the Sun's rotation period.

Joshua E. Barnes (barnes@ifa.hawaii.edu)
Last modified: October 9, 2006
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