SKYWATCH PROJECT:

MOTION OF THE SUN ALONG THE HORIZON

EQUIPMENT REQUIRED: Your eyes, a camera or sketch pad, a compass.

TIME REQUIRED: A few minutes on as many evenings and/or mornings as possible during the quarter.

BACKGROUND: Contrary to popular opinion, the sun does not always rise and set at the same spot on the horizon, and there are in fact only two days each year when it rises exactly in the east and sets exactly in the west. For this Skywatch, you will establish this fact for yourself.

WHAT TO DO: Choose a convenient spot with a reasonably clear horizon. On as many evenings/mornings as possible (at least 10-15 would be nice), observe the sunsets/sunrises from this same spot and, with the aid of landmarks on the horizon (whose compass positions must be measured at one time), record the precise position (as well as you can determine) and time at which the sun sets or rises. Weather will obviously be a problem, but you will find that you can probably determine the sun's position even through moderately thick clouds.

ANALYSIS: Make a chart on which all the positions are plotted; each point should be labeled with date, time of sunset/sunrise, and azimuth (defined as the angle along the horizon from north: north = 0 degrees, east = 90 degrees, etc.). A simple chart is sufficient, though more artistic variations are of course welcome. A telephoto shot or a blow-up of a photograph would be another good way to make your basic chart, or even to show your observations. Remember that compass needles point to magnetic north, which is approximately 18 degrees east of true north in the Seattle area.