December Sky Talk | Moon Occults Aldebaran!

In its monthly eastward orbit around the sky, our lovely satellite often passes in front of (or occults) objects beyond it, including planets, stars and even entire star clusters like the famed Pleiades.  Late on the evening of December 12th the nearly full Moon will cover one of the brightest stars in the sky for much of North America.

The beautiful fiery-orange star Aldebaran in Taurus warms the hearts of observers on cold winter nights.  It lies northwest of Orion, whose three belt stars point directly to it—as a glance at your Scientifics Star and Planet Locator will show.  When evening falls on the 12th, the nearly full Moon will be rising in the eastern sky in Taurus but by occultation time it will have moved to high in the south.

Normally, an occultation of a bright star or planet would be a naked-eye event, especially when most of the leading edge of the Moon is still in darkness. This time its slow approach toward Aldebaran over a period of hours will be visible without optical aide. But it will be so bright that binoculars will likely be needed to see the actual disappearance itself.  One technique that may make it visible to the eye is to hold a piece of cardboard at arm’s length to block most of the Moon’s bright surface.  But you have to be careful to not cover the left edge of the Moon where Aldebaran will be disappearing!  It’s best to be sitting comfortably in a lawn chair to help keep your aim steady.

Aldebaran’s disappearance will be instantaneous, but assigning an exact time is a bit tricky since it depends on both an observer’s latitude and longitude.

As an example, for those living along the East Coast, the occultation is scheduled for:

  • 11:09 p.m. EST  for Jacksonville
  • 11:10 p.m. EST for Norfolk
  • 11:13 p.m. EST for New York
  • 11:18 p.m. EST for Boston

Going inland changes this by a few minutes earlier.  Washington DC, for example, is scheduled at 11:07 and Tallahassee is scheduled for 10:57.  The best advice is to go outside at least 15 minutes before the scheduled time so you are sure to not miss the disappearance.  This give you time to watch the Moon creep up on Aldebaran before covering it.  Even if you do miss the actual occultation at the instant it happens, you will have the thrill of seeing a star that was there just minutes before no longer in the sky!

Finally, here’s an interesting aside to this event. Not only is a star blocked out by the Moon this month but an entire meteor shower!  The annual Geminid display (which many consider the best of the year) on December 13-14 will be washed out by moonlight from the full Moon on the 13th.

— James Mullaney

Former assistant editor at Sky & Telescope magazine & author of nine books on stargazing.  His latest, Celebrating the Universe!, is available from