Astronomy 102, Fall 2004
Homework Assignment #4
This homework set is due at the beginning of class on Friday, September 25. 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.
Compare radio photons (assume a wavelength of 1m), and ultraviolet photons (assume a wavelength of 100nm, remembering that one nanometer (nm) is 10-9m).
(a) If you have the same amount of energy in both kinds of photons, will you have the same number of photons, or will there be more of one kind? If so, of which kind will there be more?
(b) How many photons of one type does it take to make up the energy of a single photon of the other type? Indicate clearly which type(s) of photon you have only one of.
Refer to the H-R diagrams on p. 226 and 227 of your text. The star Vega is a star that's about three times as massive as the Sun.
(a) What is the spectral type of Vega? Is Vega bluer or redder than the Sun?
(b) What is Vega's Luminosity in units Solar Luminosities?
(c) What is Vega's temperature in K?
(d) Using Figure 11-13 in your text, and what you know about sizes, brightnesses, and temperatures, estimate the radius of Vega in both km and Solar Radii.
Assume that the amount of fuel available to power a star is proportional to its mass. (That is, assume a star is always able to use the same fraction of its mass as fuel for producing energy.) If the Sun is going to shine for 10 billion years, how long will Vega shine?
The problems below are optional; they need not be turned in, and they will not be graded.
Chapter 11, Question 5 in Pasachoff & Filippenko.
Chapter 11, Question 6 in Pasachoff & Filippenko.
Chapter 11, Question 19 in Pasachoff & Filippenko.