SKYWATCH PROJECT: PLANETARY MOTIONS

EQUIPMENT REQUIRED: None but your eyes.

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

BACKGROUND: The word "planet" comes from the Greek for "wanderer"; the Babylonian word meant "wild sheep"! The planets were recognized as celestial objects that changed their positions in a complex manner (although with discernible patterns) from night to night with respect to the background stars. In this project, you will do as the ancients did, and follow the motion of a planet over the quarter.

WHAT TO DO: Choose a planet or planets to follow. This quarter the best are Venus, Jupiter, and Saturn. Venus is extremely bright in the southwest immediately after sunset, and will move quite a bit over the quarter. Jupiter and Saturn are close to each other (Jupiter is much the brighter), high in the southeast at sunset and higher in the southern sky through the evening. In addition to measuring the position of Jupiter or Saturn relative to nearby stars, you will find it interesting to accurately measure their separation from each other.

As often as possible (try to observe the planet on at least 5-10 nights spread over as much as posible of the quarter) find the planet and determine as accurately as possible its position with respect to a couple of nearby reference stars. “Hand-span-at-arm's-length" estimates are acceptable, but much better is to use your cross-staff for measuring angles from a few reference stars.

ANALYSIS: Using your measurements and a (circle-drawing) compass, show the positions and dates on a Xerox copy of a suitable large-scale star atlas. Your T.A. can provide you with a good one. Also make a sketch of the solar system (from the outside) showing the planets' orbits about the sun, and how your planet moved relative to the (also moving!) earth over the quarter.