As the Moon rises this evening for those of us in the United States, it might look just the tiniest bit fainter than usual. That’s because the Moon will be sliding through the outer portion of Earth’s shadow, the penumbra. But the penumbra is quite faint, so it won’t produce a spectacle — just a barely-there shading that most of us won’t notice at all.
The Moon will produce plenty of spectacle all on its own, though, because it’s full. As the first full Moon after the Harvest Moon, it’s known as the Hunter’s Moon. In times gone by, hunters used the bright moonlight to help them track game through the barren fields.
Lunar eclipses occur only during a full Moon, when the Moon is directly opposite the Sun in our sky. That alignment allows it to pass through Earth’s shadow, which extends far into space. But there’s not an eclipse at every full Moon because the Moon’s orbit is tilted a bit relative to Earth’s orbit around the Sun. So most months, the full Moon passes a little above or below the shadow.
At least twice each year, though, it passes close enough to the plane of Earth’s orbit to create an eclipse. Some eclipses are penumbral, like tonight’s. Others are partial, which means the Moon is partially covered by the dark inner part of Earth’s shadow, the umbra. And the best of all are total eclipses, in which the umbra covers the entire lunar disk — briefly darkening the otherwise-bright face of our satellite world.
Script by Damond Benningfield, Copyright 2013
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