SKYWATCH PROJECT:

MOTION OF THE MOON AGAINST THE STARS

EQUIPMENT REQUIRED: Your eyes and a good star map of the sky (available from your T.A.).

TIME REQUIRED: A few minutes on 10-15 nights over the quarter.

BACKGROUND: The moon changes its position in the sky from day to day as a consequence of its orbital motion around the earth. In this project, we ask you to chart the motion of the moon against the background stars.

WHAT TO DO: Just observe the moon on as many nights as possible, estimating its position in the sky using a star chart. For some phases of the moon, especially around last quarter, this will mean getting up for a few minutes at weird hours of the morning.

On a star chart, mark the position of the moon, its approximate phase (sketch its shape), and the time at which you observed. In order to gauge the moon's position, your cross-staff can be useful to measure the angular distances between the moon and nearby stars that appear on your chart.

Also at one time try to obtain a pair of binoculars and make a reasonably accurate sketch of the surface features visible on the moon. It is easiest to see features at first or third quarter, since shadows are then more pronounced. Compare your sketch with a standard map -- you should be able to recognize 10-15 features (specific maria ("seas"), craters, mountain ranges, etc.). Even without binoculars, make the best sketch you can with the naked eye.

How closely does the moon follow the ecliptic? Does it retrace its path exactly a month later? How much of the difference could be due to the accuracy of your observations and how much could be real? How does the pattern of phases correlate with the moon's changing position relative to the sun?