It may not seem like much when you 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 us to refine our knowledge of the moon’s orbit and even 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 Spica that becomes the star of the show. Spica is the bright white star that marks the shaft of wheat held by Virgo, the maiden, and you can now see it low in the eastern sky before dawn.
And on the morning of Wednesday, Nov. 27, it will co-star with the waning crescent moon in just such an occultation.
As the moon approaches Spica from its upper right, keep a watchful eye on the star until it winks out instantly behind the moon’s bright 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, might be a challenge for some, since the event may occur during bright twilight where you live.
Viewers around the country will view the event from different angles, so its times will differ from place to place.
From New York City, for example, Spica will disappear at around 5:36 a.m. EST and reappear at around 6:51 a.m. EST. In Chicago, the occultation will occur at around 4:29 a.m. CST and end at around 5:38 a.m. CST.
Farther to the west, near Denver, viewers will miss the beginning of the occultation since the pair will be below the horizon, but the star will reappear on the upper right side of the moon at 4:21 a.m. MST.
Unfortunately, from the West Coast, the event occurs before the moon and Spica rise.
The key is to begin your watch at least 10 or 15 minutes early; also, don’t turn away as the star appears to close in on the moon.
To get the event’s times for your location, call your local planetarium, science museum or observatory, or click here for more information.
The times are listed in Universal Time, which you must convert into your local time. To get PST, for example, simply subtract 8 hours from UT; for MST, subtract 7 hours; for CST, subtract 6 hours; and for EST, subtract 5 hours.
If weather should interfere, or you miss the split-second disappearance or reappearance, don’t worry. We’ll get to see occultations of other planets and stars during the next year.
