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.
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.
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