Publications Topics:

Books

ASP Conference Series

Monograph Publications

IAU Publications

Books of Note

Purchase through the AstroShop

Journals

Publications of the ASP (PASP)

Magazines

Mercury Magazine

Archive

Guidelines for Authors

Order Mercury Issues

Mercury Advertising Rates

Newletters

The Universe in the Classroom

ASP E-mail Newsletters

Special Features

Astronomy Beat

Contact Us

Mercury, March/April 1997 Table of Contents

James C. White II
Middle Tennessee State University

Michael Vincent Mecca Durisen

Rarely have most of us really watched a lunar eclipse. Let's observe the lunar eclipse this month and see what the shadow-play can teach us about Earth and its little mate.

This month's project: Observing a partial lunar eclipse

My earliest eclipse memory involves wood-gathering. I lived on a farm in Tennessee, and my parents planned a wiener (read "weenie" in the South) roast the night of a lunar eclipse. My dad and I took the tractor down to the edge of the woods and gathered fallen tree limbs for the fire. My grandparents came out, we sat on bales of hay in a field, ate our hot dogs and roasted marshmallows, and watched a huge full Moon fall into Earth's ruddy red shadow. Big round bites were taken out of the glowing Moon as the night advanced, but, unfortunately, I fell asleep before totality...

To view my first total lunar eclipse, I checked to make sure it was clear. I had the best conditions I could ask for, considering I live in Indiana. There were too many houses where I lived and also too many streetlamps, making the Moon harder to see. It was important for me to be able to see the horizon, because the Moon would rise eclipsed. I went with my parents to the closest park because it allowed us to see more of the sky and was darker there. I used binoculars to get a closer and more detailed look at the Moon. This allowed me to see the color, structure, and shadow line on the Moon better.

Lunar eclipses are quietly impressive sights. As the Moon trundles in its orbit around Earth, it occasionally passes through our world's shadow, and our bright tiny companion is slowly devoured by darkness. This event can occur only when the Moon is opposite the Sun in our sky ­ at a position we label a full Moon, since we can see all of the Moon's illuminated side.

Earth, like the Moon, is just a big ball, and you know from looking at a basketball that a ball always casts a round shadow. The ancient Greeks knew this, too, and they saw Earth's circular shadow on the Moon during lunar eclipses. So forget the notion that ol' Chris Columbus was the one who discovered Earth to be round. He, like other learned people in his era, knew from those Greek eclipse observations that our planet is just a big ball.

But wait a minute, you say, why don't we have a lunar eclipse at every full Moon? The Moon's orbit is tipped relative to Earth's orbit around the Sun. Because of this, a full Moon will sometimes pass below Earth's shadow, sometimes above. On rare occasions, that full Moon will slip partially or totally through the shadow. Then is the time for festivity, for visiting parks and roasting weenies.

Observing Guidelines

Naked-eye observing of lunar eclipses is easy, fun, and safe. No special apparatus, no safety precautions. But to make this eclipse special, let's make some detailed observations. We suggest the following equipment: binoculars (7x50s or 10x50s), a set of lunar maps from your local bookstore, a sketch pad, a watch, pencils, and an enormous thermos of hot chocolate. Lunar eclipses last several hours.

With your observing utensils, head outside and find a comfortable viewing location. If it's cloudy, you've got problems; just keep checking the skies and hope they clear. The eclipse begins at 8:41 p.m. EST when the Moon enters the faint penumbral, or outer, part of Earth's shadow [see SkyTalk, January/February, p. C-4]. On the West Coast, the Moon will already be in eclipse when it rises around 6 p.m. While you're out, look for Mars (near the Moon) and Comet Hale-Bopp (in the northwest).

At 9:58 p.m. EST, the Moon is first touched by the dark umbral shadow. Using your binoculars and lunar map, record the times when individual lunar features fall into shadow. Ninety-two percent of the Moon will be covered by umbral shadow at mid-eclipse, 11:39 p.m. EST.

You will observe that the Moon does not just disappear during the eclipse. How does its color change? Keep track of those changes and when they occur. Rather than going completely dark, the Moon will look reddish, because Earth's atmosphere acts as a huge lens bending red sunlight onto it. Basically, the Moon is being lit by all the sunsets and sunrises everywhere on Earth. Three hours after mid-eclipse, the Moon will completely re-emerge, and you can go to bed.

Make a series of sketches, annotating them with musings (come on, let the experience touch you). At what time can you, like the ancient Greeks, detect the curved shape of Earth's shadow? If you're mathematically inclined, calculate the speed of the shadow across the lunar surface. You'll have the times when specific features are eclipsed, and with the scale on your lunar map, you can estimate the shadow's speed.

Please submit your completed report (for guidelines, see Guest Observer, November/December 1996, p. 10) by May 31, 1997 by email to jwhite@physics.mtsu.edu or by regular mail to Jay White, Attn: Guest Observers, Department of Physics and Astronomy, Middle Tennessee State University, Murfreesboro, Tenn. 37132. The selection committee will evaluate the reports and choose the Guest Observer for publication in a future issue.

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.

MICHAEL VINCENT MECCA DURISEN is a 12-year-old junior astronomer in Bloomington, Ind. You can reach him via his dad at durisen@cthulhu.astro.indiana.edu.