Dennis Mammana | Stargazers: Watch a star wink out during a lunar occultation

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It may not seem like much when you hear or read a description, but once you see one with your own eyes you'll understand why it's so special. I'm referring to the phenomenon astronomers know as a lunar occultation.

A lunar occultation occurs when the moon in its orbit around the Earth drifts in front of a more distant object — for example, a planet, star or star cluster — and blocks it from view for about an hour or so.

Occultations of stars are important because they allow scientists to refine our knowledge of the moon's orbit, and even to discover companion objects orbiting distant stars. In fact, it was a faint companion star orbiting the red supergiant Antares that first showed up during a lunar occultation in the early 19th century.

But this week, it will be Aldebaran that becomes the star of the show. Aldebaran is the reddish-orange star that marks the "fiery eye" of Taurus, the bull, and you can see it shining brightly high in the eastern sky just after dark this week. And on the evening of Tuesday, Jan. 19, it will co-star with the waxing gibbous moon in just such an occultation.

As the moon approaches Aldebaran from the west, keep a watchful eye on the star until it winks out instantly behind the moon's darkened edge. This occurs for two reasons. The first is that the star is so distant that it appears as only a point of light in our sky. The second is because the moon has no atmosphere to dim the star's light before blocking it completely.

Watching the star disappear and reappear, however, can be a challenge, though. While the celestial event will be visible with the naked eye, the moon is so bright that night that the star Aldebaran will pale by comparison and you may need binoculars or a small telescope to see it.

Because viewers around the country will view the event from different angles, its times will differ from place to place. From New York City, for example, Aldebaran will disappear at around 9:32 p.m. EST and reappear at around 10:42 p.m. EST.

The key is to begin your watch at least 10 minutes early and don't turn away!

To get the event's times for your location, call your local planetarium, science museum or observatory, or visit the following website: lunar-occultations.com/iota/bstar/0120zc692.htm. Times there are listed in Universal Time, which you must convert into your local time. To get EST, for example, simply subtract 5 hours from UT.

If weather should interfere, or you miss the split-second disappearance or reappearance, don't worry. You'll get a few more chances this year!

Visit Dennis Mammana at www.dennismammana.com.


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