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October's Lunar Eclipse (Wednesday, October 27, 2004)
October 03 , 2004 by George MuncasterThe Full Moon shrinks into a Crescent Moon and then turns into a dark reddish blur in the sky just after sunset on the evening of Wednesday, October 27th. Later – after 10 p.m. – the Moon again appears Full!
These unusual events mark the last Total Eclipse of the Moon visible from the U.S.A. until 2007. Arizonans will see the eclipse start at 6:16 p.m. (about 40 minutes after sunset) and we can watch the eclipse end just before 10 p.m. Mountain Standard Time (MST). Persons living east of Arizona will see the entire eclipse occur higher in the sky, while persons on the West Coast will see the Moon rise already partially in eclipse.
Lunar eclipses occur when the Moon's path carries it into the Earth's shadow. Since the Earth's shadow points directly away from the Sun, this means a lunar eclipse can only occur at the exact time of a Full Moon. Ordinarily, we cannot detect the Earth's shadow in the sky -- except as a dark purple band low in the east a few minutes after sunset or low in the west just before sunrise. But we will certainly see the Earth's shadow when the Moon enters it during the October lunar eclipse! Because the exact path of the Moon in each eclipse is different, the appearance of each eclipse in the sky is also unique. The October eclipse is special because it is a moderately deep eclipse and because it will begin when the sky is still somewhat bright after sunset.
A Full Moon occurs when the Moon and Sun are lined up in the sky on opposite sides of the Earth. While this occurs about 13 times each year, a total lunar eclipse is not guaranteed, because the Moon’s motion most often carries it above or below the Earth’s shadow. However, when a total eclipse DOES occur, as it will on Wednesday, October 27th, observers on the entire hemisphere of the Earth which faces the Moon can watch the sunlit Moon become shadowed, nearly disappear, and then appear again over a period of just a few hours. Because the eclipse starts so soon after sunset, to see this ENTIRE eclipse, however, Arizonans MUST observe from a location with a clear view well down to the eastern horizon. Binoculars or a small telescope may help observers enjoy the spectacle.
Here's what you should see (if our weather is clear!):
Look for the Full Moon to peek over the horizon on the evening of October 27th at 5:40 p.m. MST at a point about 20-degrees NORTH of due East. Two minutes later the Moon will be completely above the horizon. Then, for 35 minutes, a "normal" Full Moon will loom large on the horizon and gradually move higher in the sky. At about 6:16 p.m. MST, when the Moon will be 8-degrees (about the width of a fist held at arm's length) above the horizon, a small black "notch" will appear on the Moon's Eastern edge and will gradually enlarge! This is the Earth’s shadow, and the PARTIAL eclipse phase has begun.
By 6:40 p.m. the Moon will have moved halfway into the Earth's shadow and will appear much like a 1st quarter Moon. After about 7:00 p.m., the Moon will resemble a crescent Moon. Less than 30 minutes later, at 7:27 p.m., the Moon will be completely inside the Earth's shadow and the TOTAL phase of the Lunar Eclipse has started. Arizonans will then see the Moon 22-degrees above the Eastern horizon, quite faint, but round again, and probably a dim orange-red in color.
For the next hour and one-quarter the Moon will move higher in the sky -- still in eclipse. Sometimes an eclipsed Moon moves directly through the center of the Earth's shadow and it becomes very dark. However, during a non-central eclipse (such as this one), much sunlight may be scattered into the shadow by the Earth's atmosphere. If October's eclipse is typical, then we should see the Moon as coppery in color -- and a very striking sight in the sky.
High above the eastern horizon at 8:44 p.m. MST, a thin sliver of sunlight again reaches the Western edge of the Moon and the total phase of the eclipse is over. For another hour and ten minutes, the partial eclipse phases repeat themselves in reverse order as the Moon emerges from shadow. At approximately 9:55 p.m., the Full Moon will again be whole and the eclipse is over.
Weather permitting, we can all enjoy this infrequent, interesting and notable event! If you miss this total eclipse, you must wait until August 28th, 2007!
NOTE: Students and amateur astronomers can make several interesting astronomical observations during a lunar eclipse. Perhaps you might want to use read more about some Lunar Eclipse Experiments which can be performed entirely with the naked eye, although a pair of binoculars or a SMALL telescope might also help.
George Muncaster is Principal at Systems Synergies LLC, a systems engineering firm serving the wireless community and aerospace-defense communities. He teaches astronomy at Glendale Community College and at Scottsdale Community College and also astronomy distance learning classes at Rio Salado College.
