Sky Talk March 2007: Total Eclipse of the Moon

Skywatchers haven’t had an opportunity to see a total lunar eclipse for more than two years now, the last one having occurred in October of 2004. This year there are actually two of them, the first of which takes place on March 3rd. (The second one will happen on August 28th).

A unique opportunity to see a totally eclipsed Moon rising at sunset will present itself on Saturday evening, March 3rd. As our radiant “Daytime Star” sets in the west, our lovely satellite will grace the eastern sky. But it may not be easy to find it! That’s partly because many readers will very likely not have an unobstructed eastern horizon, but also because the Moon will already be in totality – completely within the Earth’s dark inner shadow (known as the umbra) at that time. As evening twilight fades, you will see an eerie-looking, dull orange- or reddish-tinted ball slowly climbing the darkening sky. Totality itself begins at 5:44 p.m. EST and mid-eclipse comes at 6:21 p.m. The Moon starts moving out of the umbra at 6:58, and this partial eclipse stage finally ends at 8:12 p.m.

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! And the colors displayed have included pale oragne, copper, rose, and even blood red. Notice also 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 planet itself is round – something recognized by the early Greeks and other skywatchers of the past. And finally, realize that you’re actually seeing the Moon move in its orbit, as it passes through and then out of the shadow at roughly its own diameter eastward each hour.

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 it suspended in space. A notable exception here is Edmund Scientiifics’ marvelous Astroscan wide-field telescope. It provides a 3-degree actual field of view at a magnification of 16x. At its average distance from us of 239,000 miles, the Moon appears aboutj 1/2 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.

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

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