Friday, February 15, 2008
Total lunar eclipse visible February 20
Wednesday, February 20, will present us with a total lunar eclipse, which happens when the moon passes through the conical shadow cast by earth. The moon will be well-positioned to allow viewing the entire eclipse. Not much darkening will be visible until the moon passes from the outer lighter shadow called the penumbra, into the umbra, the darkest part of the shadow. This begins about 8:43 p.m. when the moon is in the southeast at about 36 degrees above the horizon. When the moon moves completely into the umbra (at about 10 p.m.), totality is said to begin. For this eclipse the moon does not stay totally eclipsed for long since it skims across the lower edge of the umbra instead of traveling along its diameter. Mid-eclipse occurs at 10:26 p.m. and totality ends at 10:52 p.m.
A good astronomy project for the young science student is to watch the moon move into the earth's shadow and observe that the edge of the shadow is curved, visual evidence that the earth is round. A pair of binoculars or a small telescope will make the viewing more interesting.
Note that during totality Saturn is three to four degrees east of the moon while Regulus, a little dimmer than Saturn, is one to two degrees west.
When the moon enters the umbra, it can be illuminated only by the sunlight that is refracted by earth's atmosphere. Since the atmospheric conditions are never the same for any eclipse, one cannot predict how the moon will appear during totality. Often it appears deep reddish in color for the same reason sunsets appear reddish. Greater amounts of cloud cover would reduce this coloration. Even though this is not a rapid event, it may be interesting for family members to monitor the progress to discover how dark and colorful this eclipsed moon becomes.
For further information on the eclipse, check out the February issue of the magazine Sky & Telescope.
© 2008 The Carlisle Mosquito