ASTRONOMY 101A

Lunar and Planetary Observing Assignment

Dr. Eric Wegryn

The Moon has many appearances in the sky throughout the course of a month. It may appear as a thin white crescent, a full bright circle, or not appear at all. It may be seen above the horizon in either daytime or nighttime, as its rising and setting time varies. Even the ancients recognized that the Moon is a spherical body, illuminated by the Sun, circling Earth. As it orbits around us every month, we see different portions of the lighted hemisphere, which appear to us as the phases of the Moon.

Your assignment:

Between now and 1 May 07, observe the Moon through at least one complete cycle of phases.

Like the Sun, the Moon is up above the horizon about half of the time. Because it is moving around our planet, the Moon rises about 50 minutes later each night, and its position with respect to the stars in the background constantly changes. That is to say, it moves through the constellations, which themselves do not change. A new moon rises with the Sun, and thus cannot be seen, but as the Moon moves away from the Sun, it stays up later and later each night. A full moon rises at sunset and is up all night.

The following table, when completed, may be used to help you know when and where to look for the Moon:

In addition to the Moon, the other planets of our solar system may be visible in the night sky. Mercury, Venus, Mars, Jupiter, and Saturn can be seen with the naked eye at various times of the year. For example, the Moon will be near Venus and Mercury as a waxing crescent; it will appear near Mars around full Moon (opposition).

Make observations of at least 6 different phases as the Moon progresses from waxing crescent to first quarter, waxing gibbous, full, waning gibbous, last quarter, and waning crescent. Be aware that cloudy weather may interfere with some of your observations, and note that you may need to stay up very late or get up before sunrise at least once.
Observations must be at least 3 days apart.

For each observation, make a sketch of the Moon on a clean, white sheet of paper, including the area of the sky around the Moon, noting prominent stars or constellations near the Moon, and any other features you observe. Draw and label the horizon along the bottom of each drawing, with appropriate directions (N, E, S, W, etc.) indicated. Your drawing should span about 90° of the horizon, so for example if the center of your drawing is South, the left and right edges should be roughly SE and SW. Clearly label the drawing of each phase.

Each sketch MUST include the following

1)  your name, the location, date and exact time of observation (be specific, do not just say 8 p.m., say 8:07 or 7:54 or whatever)

2)  the horizon drawn at the bottom, with the direction you are facing, e.g. E, SE, SW, etc. (the drawing should span between 90 and 180 degrees in azimuth)

3)  an altitude scale along the left edge

4)  prominent starts and constellations, drawn to show their positions (altitude & azimuth) as well as possible (use a star chart to identify them by name)

5)  the Moon (and/or planets) in the correct position with respect to those stars. Accurately sketch the lunar features, paying attention to the orientation of the terminator, and the horns if crescent

6)  any notes describing the observation, such as weather conditions, color or brightness of stars and planets, your impressions, etc.

At least one of these observations must include the planets Mercury, Venus, Mars, Jupiter, and/or Saturn.

You should make one observation as soon as possible (i.e. within the next couple of days), and at least 5 more at approximately semi-weekly intervals. Do not procrastinate. This project cannot be done at the last minute. You must catch the Moon; it will not make an appearance just for you!

In addition to your sketches, answer the following questions (in complete sentences):

1.  Explain what causes the phases. How do the Moon&lsqous rise/set times correlate with phase?

2.  Describe what causes a lunar eclipse, and a solar eclipse. Explain why we don't see eclipses every month.

3.  Did the full Moon look larger to you when it was near the horizon? Could you measure any differences (say, by holding up a ruler at arm's length) between the angular size when it was near the horizon, and the angular size as it rose up overhead? (Try it.)

4.  Compare your sketch of the full Moon to the visible portion of any other phase. Do you see the same surface features in the same places? (Bear in mind, things look a bit different when illuminated from different angles.) If the face of the Moon always shows the same features, what does this tell us about the rotation period of the Moon?

Turn this observing project in by the end of the term.

EXTRA CREDIT

If you have a camera, or can borrow one, try to take some pictures of the Moon when it is near a bright star or a planet (e.g. Saturn or Jupiter). Photographs may be turned in with the lab report for up to 5 extra credit points, providing they come out well. Images, as with the sketches, will be judged not on artistic standards, but as scientific observations, so they should be properly exposed and include the same features listed above for sketches (you may write on the photos).