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Mercury, March/April 1996 Table of Contents

by James C. White II, Middle Tennessee State University

(c) 1996 Astronomical Society of the Pacific

Just above our heads is a world with a story. The Moon exercises no small amount of influence on our planet and on us (both physically and romantically). Learn your Moon and listen to its tale.

This month's project: Becoming a Moon lover

Do you recall Gwen Conliffe's warning in "The Wolf Man"? Even a man who is pure in heart and says his prayers by night, may become a wolf when the wolfsbane blooms and the autumn Moon is bright. People always have felt the lure of the Moon, as shown by the lunar rites practiced 5,000 years ago in northeast Scotland and the contemporary myth that people go wild during full Moons. But we don't need to call on the supernatural to experience the mystique of Earth's only natural satellite; its real history is enough to wow even Merlin.

Before oceans or grass, 4.5 billion years ago, Earth was a large ball of molten rock. Swinging in its orbit around the young Sun, our planet was sweeping up any material that wandered into its path -- a planetary dustmop. Other planets and would-be planets were doing the same. One day, Earth smacked into one of those other agglomerating worlds, a wandering object the size of Mars. The Comet Shoemaker-Levy 9 collisions with Jupiter in 1994 were a bug on the windshield compared to this wreck. Huge chunks of Earth's mantle, as well as most of the colliding body, were flung out into space. Eventually this material coalesced into our Moon.

This scenario is based upon observations made largely by the Apollo missions. Scientists used to believe the Moon and Earth were fraternal twins: two unequal parts of a large, spinning, hot blob of rock that split in two and cooled. But this hypothesis can't explain why the Moons orbit is tipped relative to the Earth's equator. Nor does it account for the shortage of iron in Moon rocks. If Earth and Moon formed from the same material, they should have the same composition.

In another scenario, the Moon was an adopted daughter: It formed elsewhere in the solar system, passed too near Earth, and was captured intact. But it isn't easy to capture a satellite. The Moon would have been moving too fast, zipping past Earth before the two bodies could have had a proper greeting, much less grown attached to each other. The giant-impact hypothesis, in which a Mars-sized object tore apart the Earth, is the best explanation to date.

Observing Guidelines

I suggest you start after March 19 or April 17, the time of the new Moon. To conduct your lunar studies, find a Moon map at your local library or bookstore; many popular astronomy books include maps that identify lunar features. In addition to your maps, you'll need a pair of binoculars (7x50s or 10x50s are good) or a small telescope.

With maps, binoculars or telescope, and sketch pad and pencils, you are ready for full-fledged Moon watching. And if you've never really paid attention to the way the Moon's appearance changes over the course of a month, you're in for subtle delights. Note the following:

• changes in the apparent color and shape of lunar features such as craters and maria
• the appearance of structures near the terminator, the line between night and day (mountains and crater rims near the terminator cast nice shadows, which shorten or lengthen as the lunar day advances)
• the appearance of the Moon during the day (ever noticed how crisp a first-quarter Moon looks on a bright, clear day?)

Finally, as a reward for your diligent observations, make sure to catch the full Moon on the evening of April 3 or 4. A gorgeous total lunar eclipse will be visible for many of us [see SkyTalk, p. 20]. I encourage you to include observations of this eclipse in your report.

What to Do With the Observations

Please submit your completed report by May 31, 1996 by email to 2032694@mcimail.com or regular mail to John Isles, Attn: Guest Observers, 1016 Westfield Drive, Jackson, Mich. 492033630. Please do not send them to the ASP office! The selection committee will evaluate the reports and choose the Guest Observer for the September/October issue.

For additional information, visit our World Wide Web site at http://www.physics.sfsu.edu/asp/mercury/observer.html. Send your comments and suggestions for future projects to James White at jwhite@physics.mtsu.edu or Department of Physics and Astronomy, Middle Tennessee State University, Murfreesboro, Tenn. 37132.

JAMES C. WHITE II is a professor in the Department of Physics and Astronomy at Middle Tennessee State University in Murfreesboro. His email address is jwhite@physics.mtsu.edu.

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