Canku Ota - A Newsletter Celebrating Native America
January 29, 2000 - Issue 02

Lunar Eclipse
By Paul Barry
Our thanks to Ronald Gehrman for the great photographs. Thank you friend.

I suppose many of you saw the lunar eclipse that happened on January 20th. It was a very interesting thing to see. Lunar eclipses do not happen every day or even every month. Those you who live out west will have another chance to see a total lunar eclipse in the early morning hours of July 16th. Here in Minnesota, we will have to wait until May 16, 2003.

We know that the lunar eclipse happens when the earth's shadow falls on the moon. It is a little more complex than it seems as first look. So here are some more details about how a lunar eclipse happens.

Although the moon revolves around the earth once each month, its orbit is not quite inline with the earth's orbit of the sun (It is tilted about 5 degrees with respect to the earth's). So, when the moon passes behind the earth (in relation to the sun) during its monthly orbit, it usually passes north or south of the earth's shadow. (The earth's shadow is a cone that -- at the moon's distance from the earth -- is about twice as wide as the moon's width.) But every few months, the moon passes either partially or completely into the earth's shadow, and a partial or total lunar eclipse happens.

The earth's shadow has two areas ... the darker inner cone, the umbra, from which the sun cannot be see at all, and an outer cone, the penumbra, where part of the sun can be seen. Most of the penumbra is not dark enough to have much effect on the brightness of the moon. Penumbral eclipses are largely ignored or unnoticed.

During a partial eclipse, the umbra of the earth's shadow advances over part of the moon's surface and then moves off the other side. No other effect is seen.

During a total lunar eclipse, the umbra contacts the moon and then slowly covers the moon until the moon is totally covered. Then, for an hour or two, the moon is immersed in the earth's shadow. Though no sunlight falls directly on the totally eclipsed moon, some sunlight is bent around by the earth's atmosphere. The blue light is removed from this refracted sunlight when it is scattered in by the earth's atmosphere. This creates the blue skies overhead for the people on earth; only the red light gets through to the moon. So, a totally eclipsed moon appears reddish. Just how reddish depends on whether there is volcanic dust in the earth's atmosphere; the dust makes the moon look darker and less reddish. Giant storms or cloudy regions on earth can effect the earth's shadow, perhaps making the darkness of the shadow appear uneven on the moon. The moon will also appear less evenly illuminated if it passes closer to the sides of the umbra rather than through the umbra's center.

Eclipse Home Page

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