Bob Moler's Ephemeris Blog

On the early morning of November 26th, that’s Thanksgiving morning here in the US,  The Moon will pass in front of, or occult, the bright star Aldebaran in Taurus the bull.  The event is called an occultation.

Three first magnitude stars can be occulted by the Moon,  Aldebaran, Regulus in Leo the lion, Antares in Scorpius the Scorpion, and Spica in Virgo the virgin, since these stars lie within 5 1/2 degrees of the ecliptic, the plane of the Earth’s orbit.  The Moon’s orbit is inclined to it by 5º 14′.  Also because the Moon’s orbit precesses over a period 18.6 years they occur over the Earth in monthly series every 18.6 years.  There are 43 monthly occultations that will occur in this series, which actually started in January.  This is the best of them so far.  We’ll have another on the evening of January 19th next year.  Below is a chart of the event from the Astronomical Almanac Online which can be accessed here:  http://asa.usno.navy.mil/.

Map of the area where the occultation of Aldebaran is visible. Credit: Astronomical Almanac Online – U.S. Nautical Almanac Office, United States Naval Observatory (USNO), in the United States and Her Majesty’s Nautical Almanac Office (HMNAO), United Kingdom Hydrographic Office (UKHO), in the United Kingdom.

The occultation will be visible for locations within the nested grid of curved lines.

The two important events of the occultation is the star’s disappearance and reappearance.  The times of these two events depend on your location, and are scientifically useful in determining the precise position of the Moon.

I’ve worked out the timings for my location about half way between Traverse City and Interlochen, so they should be within a couple of minutes of your observed time if you’re within 30 or so miles.  Go out early, the earlier the better.  The Moon will be especially bright, being only 12 hours after the instant the Moon will be full.  Binoculars or a small telescope will be necessary to spot Aldebaran.  The farther away Aldebaran is away from the Moon the easier it can be picked up.  Note as a rule of thumb, the Moon moves its own diameter against the stars in about an hour.

For the Traverse City/Interlochen area I calculate the disappearance of Aldebaran at 5:38 a.m.

Aldebaran just prior to it’s disappearance behind the Moon from Interlochen/Traverse City. Created using Cartes du Ciel (Sky Charts).

For the Traverse City/Interlochen area I calculate the reappearance of Aldebaran at 6:29 a.m.

Aldebaran just after it’s reappearance from behind the Moon from Interlochen/Traverse City. Created using Cartes du Ciel (Sky Charts).

The Moon will be low in the western sky.

Timings for 3 locations in Michigan

This can be used to approximate the occultation time for other locations in Michigan.

City(s)                    Disappears  Reappears Location
Ironwood          5:33 a.m.   6:25 a.m. Northwestern corner of the
                                        Upper Peninsula (UP) of
                                        Michigan
Interlochen/      5:38 a.m.   6:29 a.m. Northwestern lower Michigan
   Traverse City
Monroe            5:45 a.m.   6:29 a.m. Southeastern corner of Michigan

Estimating timings for your location

I used Cartes du Ciel the free software that I have a link to on the right.  Make sure that the program is set for topocentric positions under Setup/Solar System.  And you have entered your position under Setup/Observatory.  You can find your location in Google Earth.

You can also use Stellarium.  Just make sure the Moon is normal sized.

In both programs you can lock the Moon or Aldebaran in the center of the screen Pick a time in advance of the occultation and using the set time window walk the star towards the Moon, mark the time.  Then walk the star out from the Moon and record the reappearance time.  That’s it.

This should work with other planetarium programs too.