Post-Event: Pictures of the eclipse are here.
Enthusiastic skywatchers try to never miss a total eclipse of the Moon. The
spectacle is often more beautiful and interesting than one would think. The
next opportunity is Wednesday, Oct. 27.
The Moon, normally lit by sunlight, will enter and later emerge from the shadow
of Earth. Much of the change will be obvious. But secondary phenomena may be
overlooked.
This chronology includes some of the things you might expect to see. Probably
not all of those mentioned will occur because no two eclipses are exactly the
same. But many will, and those who know what to look for have a better chance
of seeing it!
The Stages: What to Expect
1) Moon enters penumbra - The shadow cone of the
Earth has two parts: a dark, inner umbra, surrounding by a lighter penumbra.
The penumbra is the pale outer portion of the Earth's shadow. Although the
eclipse begins officially at this moment, this is in essence an academic event.
You won't see anything unusual happening to the Moon - at least not just yet.
The Earth's penumbral shadow is so faint that it remains invisible until the
Moon is deeply immersed in it. We must wait until the penumbra has reached roughly
70 percent across the Moon's disk. For about the next 50 minutes the Full Moon
will continue to appear to shine normally although with each passing minute
it is progressing ever deeper into the Earth's outer shadow.
2) Penumbral shadow begins to appear
- Now the Moon has progressed far enough into the penumbra so that it should
be evident on the Moon's disk. Start looking for a very subtle light shading
to appear on the Moon's left portion. This will become increasingly more and
more evident as the minutes pass; the shading appearing to spread and deepen.
Just before the Moon begins to enter the Earth's dark umbral shadow the penumbra
should appear as an obvious smudge or tarnishing of the Moon's left portion.
3) Moon enters umbra - The Moon
now begins to cross into the Earth's dark central shadow, called the umbra.
A small dark scallop begins to appear on the Moon's left-hand (eastern) limb.
The partial phases of the eclipse begin; the pace quickens and the change is
dramatic. The umbra is much darker than the penumbra and fairly sharp-edged.
As the minutes pass the dark shadow appears to slowly creep across the Moon's
face. At first the Moon's limb may seem to vanish completely inside of the umbra,
but much later, as it moves in deeper you'll probably notice it glowing dimly
orange, red or brown. Notice also that the edge of the Earth's shadow projected
on the Moon is curved.
Here is visible evidence that the Earth is a sphere, as deduced by Aristotle
from lunar eclipses he observed in the 4th Century BC. Almost as if a dimmer
switch was slowly being turned down, the surrounding landscape and deep shadows
of a brilliant moonlit night begin to fade away.
4) 75 percent coverage - With three-quarters
of the Moon's disk now eclipsed, that part of it that is immersed in shadow
should begin to very faintly light up . . . similar to a piece of iron heated
to the point where it just begins to glow.
It now becomes obvious that the umbral shadow is not complete darkness. Using
binoculars or a telescope, its outer part is usually light enough to reveal
lunar seas and craters, but the central part is much darker, and sometimes no
surface features are recognizable. Colors in the umbra vary greatly from one
eclipse to the next, Reds and grays usually predominate, but sometimes browns,
blues and other tints are encountered.
5) Less than five minutes to totality - Several
minutes before (and after) totality, the contrast between the remaining pale-yellow
sliver and the ruddy-brown coloration spread over the rest of the Moon's disk
may produce a beautiful phenomenon known to some as the "Japanese lantern effect."
6) Total eclipse begins - When the last of the
Moon enters the umbra, the total eclipse begins. How the Moon will appear during
totality is not known. Some eclipses are such a dark gray-black that the Moon
nearly vanishes from view.
At other eclipses it can glow a bright orange. The reason the Moon can be seen
at all when totally eclipsed is that sunlight is scattered and refracted around
the edge of the Earth by our atmosphere. To an astronaut standing on the Moon
during totality, the Sun would be hidden behind a dark Earth outlined by a brilliant
red ring consisting of all the world's sunrises and sunsets.
The brightness of this ring around the Earth depends on global weather conditions
and the amount of dust suspended in the air. A clear atmosphere on Earth means
a bright lunar eclipse. If a major volcanic eruption has injected particles
into the stratosphere during the previous couple of years, the eclipse is very
dark. But, as of this writing, no such eruption has happened, so the betting
is that this eclipse will be bright.
7) Middle of totality - The Moon is now shining
anywhere from 10,000 to 100,000 times fainter than it was just a couple of hours
ago. Since the Moon is moving to the north of the center of the Earth's umbra,
the gradation of color and brightness across the Moon's disk should be such
that its lower portion should appear darkest, with hues of deep copper or chocolate
brown. Meanwhile, its upper portion - that part of the Moon closest to the outer
edge of the umbra - should appear brightest, with hues of reds, oranges and
even perhaps a soft bluish-white.
Observers away from bright city lights will notice a much greater number of
stars than were visible before the eclipse began. The Moon will be in the constellation
of Aries, the Ram. Well above and to the right of the Moon will be the Great
Square of Pegasus while the beautiful Pleiades Star Cluster will sit far off
to the Moon's left.
The darkness of the sky is impressive. The surrounding landscape has taken
on a somber hue. Before the eclipse, the Full Moon looked flat and one-dimensional.
During totality, however, it will look smaller and three-dimensional - like
some weirdly illuminated ball suspended in space.
Before the Moon entered the Earth's shadow, the temperature on its sunlit surface
hovered at 266 degrees Fahrenheit (130 degrees Celsius). Since the Moon lacks
an atmosphere, there is no way that this heat could be retained from escaping
into space as the shadow sweeps by. Now, in shadow, the temperature on the Moon
has dropped to minus 146 degrees Fahrenheit (99 degrees below zero C).
A drop of 412 degrees Fahrenheit (229 degrees C). in less than 90 minutes!
8) Total eclipse ends - The emergence
of the Moon from the shadow begins. The first small segment of the Moon begins
to reappear, followed again for the next several minutes by the "Japanese lantern
effect."
9) 75 percent coverage - Any vestiges
of coloration within the umbra should be disappearing now. From here on, as
the dark shadow methodically creeps off the Moon's disk it should appear black
and featureless.
10) Moon leaves umbra - The dark
central shadow clears the Moon's right hand (western) limb.
11) Penumbra shadow fades away - As
the last, faint shading vanishes off the Moon's right portion, the visual show
comes to an end.
12) Moon leaves penumbra - The
eclipse "officially" ends, as it is completely free of the penumbral shadow.
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George Nguyen
and Ion Iftimie
catalogued the Nov. 8, 2003 lunar eclipse as it developed. More
Pictures >>>
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Timing of Each Stage
All times are for p.m. on Oct. 27, 2004 except when in bold italics,
which corresponds to a.m. on Oct. 28. Dashes indicate the Moon has
not yet risen above the horizon. Not included in the timetable are Hawaii
and Alaska. For Hawaiians, moonrise comes just after the end of totality,
with the Moon gradually ascending the sky and its gradual emergence from
the shadow readily visible. Across much of Alaska, the eclipse will already
be underway when the Moon comes up; over southwest Alaska, the Moon will
rise totally eclipsed, appearing like a weird, mottled, dim ball among
the twilight stars.
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Oct.
27, 2004 Eclipse Webcasts Planned (weather permitting)
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Astronomy
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Joe Rao,
a veteran of 12 total lunar eclipses, serves as an instructor and guest lecturer
at New York's Hayden Planetarium. He writes about astronomy for The New York
Times and other publications, and he is also an on-camera meteorologist for
News 12 Westchester, New
York.
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