29:50 MODERN ASTRONOMY
First Homework Set...September 1, 1999
Note: Be sure to consult the Appendices in your book.
Having problems? Don't go around confused and despondent! Ask for help! The purpose
of these problem sets is to help you learn something.
(1) A source of X-rays is brightest at a wavelength of 1 nanometer. Assume that it
is radiating like a blackbody. What is its temperature?
Answer: 
K.
(2) The Earth radiates electromagnetic radiation to space. At what wavelength is it
brightest?
Answer: 
meters = 10 microns.
(3) What is the mean (average) density of the Sun? Density is defined as the mass per
unit volume. The volume of a sphere is 
, where r is the
radius of the sphere. Compare the mean density of the Sun with that of water.
Answer 
kilograms = 1.42 times that of water. Real similar
(4) You like driving your car. You would drive it anywhere. Recently you have started
hanging around with space aliens. The aliens fix up your car so you can drive
out into outer space. The only problem is that you cannot drive any faster than
you can on Interstate 80. You decide to drive to the planet Mercury. How long does it
take you to get there? You cannot ask your space alien buddies to come along
and pick you up in their spaceship.
Answer About 100 years. It depends on how fast you drive.
(5) Using Figure 17.33, find the sunspot number at the highest sunspot maximum of the
20th century. Now, using the website connection at
http://www.sunspotcycle.com,
compare this 20th century maximum with (a) the current sunspot number and (b) the
projected number at solar cycle maximum next year.
Answer Maximum in this century is about 175. Average of last couple of months is
about 90 - 100. Prediction for next year is about 140.