Astronomy 102, Fall 2004

Homework Assignment #5

This homework set is due at the beginning of class on Friday, October 8. It must be turned in by 9:10AM that day. Late homework will not be accepted. This is includes your being late to class!

Staple. If you have more than one page, staple them together; do not just fold the corner. If you have multiple pages and do not staple, I will deduct one point from your score..

The first three problems are required. The remaining problems are optional, and will not be graded; they are here as additional review problems for you. After the homework has been graded, solutions will be posted to all problems.

Please write out the problem statement at the top of your solution. (This is for two reasons; it is so I can know which problems you answered, and that you answered the right problem from the bit. It also will make your graded homework more useful as a study aid later.)

You may consult with other students (as well as with the TAs and professor) on this homework set. However, your final answer should be your own. Do not write down an answer you don't understand, and do not "dictate" an answer to somebody else.

- (a) An astronomer detects two stars which she believes have identical luminosities. Star A has a measured parallax of 0.125". Star B is detected to be 378 times dimmer than Star A. What is the distance to star B in pc?
- (b) If one star is yellowish, and the other star is make an estimate of R_yellow/R_blue, the ratio of the two stars' radii.
One of the most famous comets in the solar system is Comet Halley. comet. This comet returns to the inner solar system and is visible every 76 years; it's last apparition was in 1986. The comet, like other periodic comets, is in a highly eccentric elliptical orbit around the Sun.
- (a)What is the semi-major axis of Comet Halley's orbit about Sun?
- (b)What is the closest and the farthest distance from the Sun to Comet Halley over the course of the comet's orbit?
- (c)Comet Halley is typically only visible from the Earth for several months out of the 76 years of its orbit. Use Kepler's laws to explain why.
- (d)When should we expect to see Comet Halley again?
Consider the following H-R diagram of two star clusters:

Each cluster is small enough that all of the stars in the cluster can be assumed to be at the same distance. Notice the log scaling of the "Brightness" axis. The tics from 1 to 10 are repeated in the other ranges; for example, the next tic above 0.1 represents 0.2, the tic above that 0.3, etc., even though they are not evenly spaced.

If Cluster A is at a distance of 1 kpc, how far away (in pc) is Cluster B? Be sure to explain your reasoning!

The problems below are optional; they need not be turned in, and they will not be graded.

(Coming soon.)