Sky Talk February 2008: Total Eclipse of the Moon

The last in a series of three total lunar eclipses occurring within less than a year of each other that began last March (with a second one this past August) will occur on the evening of February 20th. After this month’s show, skywatchers will have to wait until December of 2010 to see another total event. So this is definitely not to be missed if skies are clear that night!

If you were fortunate enough to see the previous two eclipses of the Moon that occurred over the past 11 months, you’ll now have the rare opportunity of adding yet a third such event to your observing log! This one happens on Wednesday evening, February 20th, at a time convenient even for those who have to go to work or school the next day. Partial eclipse begins at 8:43 p.m. EDT, at which time the left-hand edge of the Moon enters the Earth’s dark inner shadow known as the umbra. It will take our satellite more than an hour to become fully immersed. Totality itself then begins at 10:01 p.m. and last 50 minutes this time, after which the Moon’s right-hand edge emerges into sunlight again. It becomes fully illuminated by 11:20 p.m, marking the end of the partial eclipse stage.

There are a number of fascinating things to notice as you watch this event unfold. Most obvious are the darkness of the eclipsed Moon and the range of colors displayed, both of which vary from one eclipse to another. These depend on the clarity of the Earth’s atmosphere at the time, which refracts or bends sunlight around into the umbral shadow. There have actually been eclipses so dark that the Moon remained invisible during totality — and ones so pale that you had to look carefully to see that there was even an eclipse in progress! The colors displayed have included pale orange, copper, rose, and even blood red.

Notice too that the Earth’s shadow is curved at all phases of the eclipse as the Moon passes through it. This is direct proof that our home planet itself is round — something recognized by the early Greeks and other skywatchers of the past. Also realize that you’re actually seeing the Moon move in its orbit during an eclipse, as it passes into, through and then out of the shadow at roughly its own diameter eastward each hour. And for this eclipse, the bright star Regulus will appear above the Moon during totality and the planet Saturn to its lower left.

While lunar eclipses can certainly be enjoyed with the unaided eye alone, they are best-seen in binoculars. Telescopes, with their relatively narrow fields of view, typically don’t provide enough sky coverage around the Moon to get the full effect of its being suspended in space. A notable exception here is Edmund Scientifics’ marvelous Astroscan wide-field telescope. It provides an amazing 3-degree actual field of view at a magnification of 16x. At its average distance from us of 239,000 miles, the Moon appears about ½ degree across — so that’s 6-Full-Moon-diameters of sky! The Astroscan also makes a great instrument with which to capture the eclipse using a digital camera or camcorder for later viewing and processing.

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of five books on stargazing.


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