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Mercury, Sep/Oct 1995 Table of Contents

by James C. White II, Middle Tennessee State University

(c) 1995 Astronomical Society of the Pacific

Those who've seen a total solar eclipse say it's the most spectacular sky event you can witness. You'll get even more out of it by taking detailed notes.

This is a new Mercury feature that asks you to become an active participant in the study of the universe. Each issue we'll describe observations you can make with the naked eye or a small telescope. We'll ask you to collect some data and keep an observing log. Finally, when your observations are complete, we ask that you submit a short report of your work to Mercury. A panel of astronomers will select one report for publication in an upcoming issue. The idea is to show readers what other individuals and groups have done and to demonstrate the sense of discovery you can experience even in simple observing projects.

This Month's Project: Total solar eclipse visible from southern Asia and western Pacific

On the morning of Tuesday, Oct. 24, in the arid land south of Tehran, Iran, the Sun will fade from view. Not the culmination of ancient prophecy, but none the less mystical, Earth's small Moon will begin a slow slide past the enormous Sun. Over the next six hours, millions of people throughout southeast Asia and the western Pacific will have, weather permitting, the opportunity to experience the wonder of a solar eclipse.

The dark, inner part of the Moon's shadow, the umbra, will strike the Earth first in Iran and trace a smooth curve across Afghanistan and Pakistan, down and through northern India. For those who feel the chill of the umbra's passage, the Sun will disappear, obliterated for a few moments by the Moon's disk. The dark shadow will wade across the Bay of Bengal and run aground on Myanmar's western coast. South through Thailand, Cambodia, and Vietnam, the shadow then plunges across the South China Sea. A fleeting visit to the northern tip of Borneo and small islands of Micronesia, and the shadow finally leaves the Earth south of the Marshall Islands.

The eclipse path is determined by the position of the Moon relative to the Earth and by subtleties in the perpetual waltz of these two bodies. The Moon's orbit around the Earth is tipped with respect to the Earth's orbit about the Sun, the ecliptic. During an eclipse when the Moon is, say, above the ecliptic, the lunar shadow generally strikes the Northern Hemisphere. Because the Earth is not flat, the shadow falls on a slightly squashed, spinning ball. All the while, the Moon is moving in its orbit. Together these effects cause the eclipse path to curve gracefully across the globe, and the shadow to change size and shape and speed during its visit. Anyone near the beginning and end points will have but tens of seconds of totality; those nearer the middle portions of the path have more time to luxuriate in a midday night.

What about people outside the umbra? They will see a partial solar eclipse as the outer, penumbral shadow crosses them. A person in Calcutta will see a Sun whose face is 99.9 percent obscured, whereas someone in Penang, Malaysia will view a Sun two-thirds covered by the Moon.

This effect is short-lived, and you must be prepared to make the most of it. After totality, twilight returns and the Sun emerges for the second time that day. Roosters crow, monkies scratch their heads, and humans get back in their cars. All remember the day of two nights.

Observing Guidelines

Photographs of the eclipse are welcomed, but written descriptions are more valuable since they convey what it is actually like to be there. Try using a small tape recorder to describe what you experience -- if you do, please transcribe your recordings before submitting them -- or dictate to a companion. Note changes in sound, illumination, and air temperature. Describe the change in appearance of the Sun, Moon, and sky.

Make sure you frequently include either the local or Universal Time in your descriptions. Things happen quickly as totality approaches, and good timing is essential. The report must also give the latitude and longitude of your observing location. If these are unknown to you, provide us with the names of the nearest cities or towns, the state or province, and the country.

If you intend to use equipment in addition to your naked eyes, we encourage you to visit our World Wide Web site for additional information. Do not look directly at the Sun. It's tempting to stare at the Sun, thinking the Moon will block most of the light, but plan on using something to protect your eyes. Many eclipse trips provide mylar glasses, and issues 5 and 17 of the ASP's teachers' newsletter The Universe in the Classroom describe how to fashion simple and safe solar viewers. Readers can access these issues at our World Wide Web site or request back issues from Teachers' Newsletter Back Issues, 390 Ashton Avenue, San Francisco, Calif. 94112.

What to Do With the Observations

Incorporate your observations into a document with the following information: name of the project (such as, "October 1995 Eclipse"), your name or the name of your group, mailing address, telephone number, and email address, if available. We welcome reports from observers of all ages in all countries.

Please submit your completed report by Nov. 30, 1995 by email to 0002032694@mcimail.com or regular mail to John Isles, Attn: Guest Observer, 1016 Westfield Drive, Jackson, Mich. 49203-3630. The selection committee will evaluate the reports and choose the Guest Observer for the March/April 1996 issue.

For additional information, visit our World Wide Web site. 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 astronomical research focuses on cataclysmic variables. He writes a monthly astronomy column carried by newspapers in Tennessee. His email address is jwhite@physics.mtsu.edu.

Additional Information

NASA's October 1995 eclipse bulletin is an excellent source of information. It includes supplementary information on weather predictions along the eclipse path and advanced observing tips for those interested in collecting scientific useful data during the eclipse. And among interesting animations on the Web, the National Oceanic and Atmospheric Administration has a nice loop of the 10 May 1994 annular eclipse that was visible from North America.

Traditional paper references that may be useful include the eclipse observer's guide Chasing the Shadow: An Observer's Guide to Eclipses (1994, Kalmback Books) by J.K. Harris and R.L. Talcott, and the guide for making solar observations Observing the Sun (1991, Cambridge University Press) by P.O. Taylor.