AST 307 · Introductory Astronomy Fall 2003

AST 307
Homework #1
Due Fri. Sep. 5 (at beginning of class)

Note: on all homework questions you may work with other students and get help from them, the TA, or the professor. But you must write out your own answers, in your own words, and in enough detail for us to understand what you have done.
1. Mars was at its closest approach to Earth August 27. How long will it be until its next close approach? Hint: Use the facts that the Earth orbits the Sun in 1 year, and Mars orbits in 1.88 yr. Then ask how many times we each orbit in a century, and how many times we pass Mars in a century. You should then be able to calculate how long it is between one time we pass Mars and the next.

2. Venus has an orbital period of 225 (Earth) days. It has a sidereal rotational period of 243 days, rotating clockwise (opposite its orbital motion). Calculate the length of the day on Venus (noon to noon) in Earth days. Hint: Ask how frequently the stars appear to move across the Venusian sky (if it weren't so cloudy there) and in what direction, due to the rotation of Venus. Then ask how frequently the Sun appears to move around the celestial sphere (relative to the stars)from Venus and in what direction. Then combine the two effects to get the answer.

3. On December 8 of this year the Moon will be full. At about what time will it rise on that day (as seen from Austin)? In what direction should you look to see the moon rise on that day? Describe the path the moon will appear to take across the sky on that day (or night). Your answer should distinguish the full Moon's path in December from its path in June.
Assume that the orbit of the Moon is in the ecliptic, i.e. it is in the same plane as the Earth's orbit around the Sun.

Due Sep. 26:
1. Over the next few weeks keep an eye on the Moon. Every couple of days, and several times during at least one day, note the location of the Moon in the sky (how far above the horizon it is, what direction you turn to look at it, and if the Sun is up its angle from the Sun), the phase of the Moon (how much of it is lit), and the orientation of the lit side. You might notice other facts to note down. Keep a record of your observations. After you have made the observations, compare them to your expectations from the Copernican theory, testing the theory with your observations.

Note: The streets on campus run pretty much N-S, E-W, but the other streets in Austin do not. In central Austin, most N-S streets run about 10-15 degrees east of north, and E-W streets run about 10-15 degrees south of east.

5 September 2003
Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
prospective student inquiries: studentinfo@astro.as.utexas.edu