AST 307 · Introductory Astronomy
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Fall 2003
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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.
- 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.
- 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.
- 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:
- 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.
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