Jimmy Westlake: Partial lunar eclipse on horizon
May 21, 2012
In an eerie re-creation of last December's sunrise lunar eclipse, the full moon once again will slip into the Earth's dark shadow by the dawn's early light on the morning of June 4. This eclipse, however, will not be total for anyone on Earth. It is a partial eclipse of the moon, which means the moon's path only takes it through the edge of the Earth's shadow, not completely into it.
An eclipse of the moon occurs when the moon passes through the Earth's long shadow cast into space, either partially or totally. This can occur only during the full moon phase when the moon is opposite the sun in our sky, but it doesn't happen at every full moon because of the 5-degree tilt of the moon's orbit relative to the Earth's orbit. The full moon usually passes slightly above or slightly below the shadow cone of the Earth.
June's full moon is known in folklore as the Flower Moon. It will rise at sunset on the evening of June 3 and will show no hint of an eclipse until just before 4 a.m. the next morning. That's when the lower-left edge of the moon will begin to darken as it enters the Earth's umbral shadow. Then it becomes a race against sunrise as dawn brightens the sky. Maximum eclipse happens at 5:03 a.m. when 37 percent of the Flower Moon will be shadowed. The sun will rise at about 5:39 a.m. and the partially eclipsed moon will set only nine minutes later, at 5:48 a.m.
If you have a very clear view of the southwest horizon, you might be able to follow the eclipsed moon all the way to its setting point. Binoculars or a small telescope certainly will help. The farther west of Colorado you live, the more of the eclipse you will get to see. June's partial lunar eclipse is the closest that Colorado will come to a total lunar eclipse until April 15, 2014.
Remarkably, this unusual partial eclipse of the moon is sandwiched between two even more unusual events, the annular eclipse of the sun Sunday and the ultra-rare transit of Venus across the face of the sun June 5. I don't recall a time in my life when three such events happened in so short a timespan. Astronomically speaking, I would consider any year that contained one of these events to be a good year.
These are good times, indeed.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out Westlake's astrophotography website at http://www.jwestlake.com.
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