Red star pricks Moon balloon

For the first of 13 times this year, the Moon will on Tuesday-Wednesday night (Jan. 19/20) pass so close to Aldebaran that it occults (hides) the great “eye of the Bull.”

Occultation of Aldebaran

This detail from the “Occultations” section of Astronomical Calendar 2016 shows that the track from within which the occultation is visible – the “shadow of the Moon” cast by the remote ruddy light of Aldebaran – embraces all of the contiguous U.S. and most of Canada. Few occultation events are so favorable.

As shown by the little diagram to the right (star passing Moon as seen from Earth’s center), Aldebaran will disappear at the Moon’s dark limb (edge) and emerge from the bright one.

Seeing an occultation happen is perhaps surprisingly exciting. Seeing it happen to a bright star high in the sky should be easy. If you’d like to try, go out in early darkness (Pacific coast: evening of Tuesday Jan. 19) or nearer to midnight (mid America): there’s the Moon, “waxing gibbous,” that is, a few days before Full, therefore pretty bright. Not far to its left sparkles reddish Aldebaran. Estimate how long it will be before the two collide: the Moon moves roughly its own width in an hour. Go back in and warm up and come out, preferably with binoculars, a quarter of an hour or so before the collision.

The more centrally the star hits the Moon (which depends on how far north or south you are from the centerline of the track) the longer it will take to pass behind: up to nearly an hour. Its popping out from the other and dazzling edge will take you by surprise.

In Britain, the occultation can theoretically be seen, but in bright twilight just before the Moon sets



3 thoughts on “Red star pricks Moon balloon”

  1. “Few occultation events are so favorable.” Unless it’s raining. Those last few kilometers of Earth’s atmosphere are a total wild card.

Write a comment