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Moon and Aldebaran

January 19, 2016

Aldebaran, the bright eye of Taurus, the bull, plays a game of stellar “peek-a-boo” this evening — it’ll disappear behind the fat gibbous Moon. Its vanishing act will be visible from almost all of the United States. The exact timing depends on your location. It happens late in the evening for those on the East Coast, but in early evening on the West Coast.

This event is known as an occultation. It occurs when the Moon passes directly between Earth and a star, hiding the star for anywhere from a few minutes to an hour or so. The Moon can occult any star that lies within a few degrees of the Sun’s path across the sky. But the Moon’s orbital path is tilted a bit, so most of the time the Moon misses most of the bright stars along its path. The geometry has to be just right for an occultation to take place.

And right now, the geometry is right for a whole series of occultations with Aldebaran. The first took place about a year ago. The paths of the occultations are moving southward, and will be farthest south later this year. After that, they’ll begin to move northward again. The series will end in September of 2018. After that, the Moon won’t cover up Aldebaran again for another 15 years.

Look for Aldebaran below the Moon at nightfall, with the Moon’s dark edge creeping toward the star as the night progresses. After the occultation, Aldebaran will lead the Moon across the sky until they set in the wee hours of the morning.

Script by Damond Benningfield, Copyright 2015

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