Jimmy Westlake: Watch the moon eclipse a star
February 6, 2017
Steamboat Springs — As the moon orbits Earth, it occasionally will pass in front of a bright star and hide it from view — an event called an occultation. There are only four bright stars along the moon's path that can be eclipsed from time to time. They are Alpha Leonis (Regulus), Alpha Virginis (Spica), Alpha Scorpii (Antares) and Alpha Tauri (Aldebaran).
Mark your calendar now. Early the evening of March 4, the first quarter moon will perform a prime time occultation of the bright star Aldebaran for folks living in the western U.S. The dark, eastern edge of the moon will creep up to Aldebaran and eclipse it about 8:35 p.m.
Because the moon has no atmosphere to dim the star's light and the star itself is so distant that it appears to us as a mere pinpoint of bright light, Aldebaran will wink out in a split second. One moment it will be there and the next moment — poof — it will be gone. Start watching about 10 minutes or so before the expected occultation.
The moon will hide Aldebaran for about 50 minutes before it pops back into view about 9:25 p.m. Aldebaran will reappear on the bright edge of the moon, so its reappearance probably will be a little tougher to see with the unaided eye than its disappearance. In any case, binoculars or a telescope of any size will provide an excellent magnified view of the event.
Aldebaran is the brightest star in the constellation of Taurus, the Bull. It punctuates one end of the V-shaped Hyades star cluster that forms the Bull's face. This cluster of several hundred stars shines from a distance of 150 light years, but Aldebaran is actually a foreground star — only 65 light years away — superimposed on the cluster.
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The name Aldebaran comes from the Arabic words meaning "The Follower," because it follows the nearby Pleiades star cluster westward through the night.
Aldebaran is an orange giant star in the advanced stages of its life. Astronomers estimate that Aldebaran's radius is 44 times larger than our sun's.
To locate Aldebaran and the Hyades star cluster, simply follow a line through the three stars of Orion's Belt upward to the right. The first bright star you come to is Aldebaran. Continuing along that same line will lead you next to the Pleiades, or Seven Sisters, star cluster.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Steamboat Springs Campus. His “Celestial News” column appears monthly in the Steamboat Today newspaper. Check out his astrophotography website at jwestlake.com.