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Moon and Spica

July 15, 2013

The first-quarter Moon snuggles quite close to Spica this evening, the brightest star of the constellation Virgo. In fact, for skywatchers in the continental United States they’ll be separated by less than the width of the Moon itself. And from parts of Central America, the Moon will actually cover up the star for a while, blocking it from view — an event called an occultation.

In the past, astronomers routinely used lunar occultations to learn more about the star that was being covered up. If you know how far away a star is, for example, then the length of time it takes the star to wink out of sight reveals its diameter. And if there are two dips in the light instead of one, it means the star is a binary — two stars locked in a gravitational embrace.

Lunar occultations of stars get less attention today than in decades past, though. That’s largely because advances in technology allow astronomers to learn the same things about a star on just about any night the star is in view — not just when the Moon ambles in front of it.

Tonight, Spica stands just a whisker from the Moon as night falls. The time of their closest approach varies depending on your location, but they’ll remain quite close for the entire time they’re in view. And another object stands not far to their upper left — the golden planet Saturn, which is a bit brighter than Spica. It will be close to the Moon tomorrow night — and we’ll have more about that on our next program.


Script by Damond Benningfield, Copyright 2013

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