Sky watch: For early risers, a partial lunar eclipse

Night owls and insomniacs may be the only ones to witness a rare cosmic alignment on June 26.

Before dawn that day, the full moon will appear to drift slowly into the shadow of the Earth, creating a partial lunar eclipse.

Regular readers of this column already know that the moon moves eastward in its orbit about one full moon diameter every hour relative to the more distant stars. What we normally don't see, however, is the shadow of the Earth - unless the moon encounters it in space.

That's just what will happen June 26. On that morning, the moon's eastern edge will enter the Earth's light outer shadow (the penumbra) around 4:57 a.m. The penumbra is quite faint, and few people will notice it until just before what astronomers call "first contact." This is when the moon enters the Earth's inner dark shadow (the umbra) around 6:17 a.m.

Some East Coast viewers may see the eastern edge of the moon begin to appear slightly darker before the full moon sets behind the southwestern horizon. Just about everyone else in the United States will be able to see first contact - weather-permitting, of course.

The eclipse progresses as the moon drifts further into the circular shadow until it reaches its deepest point around 7:38 a.m., when about half of the moon will be engulfed in shadow. Much of the nation will see this around the time of moonset.

From this time on, the moon will leave the shadow and exit entirely, its "last contact," around 9 a.m.

Unlike an eclipse of the sun, a lunar eclipse is safe to watch without filters. All you need is your eyes, though viewing with binoculars or a small telescope can be fun as well. If you miss it, U.S. residents have to wait only until the night of Dec. 20-21 for the next one. On that night, the moon will be engulfed entirely by the Earth's shadow, and will provide us with a spectacular total lunar eclipse.

To learn more about how to view and photograph the lunar eclipse, visit: mreclipse.com/Special/LEprimer.html.

And after the sky show, be sure to visit spaceweather.com to see terrific photos of the sky show.