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occultation



I was wondering if anyone on the list saw the lunar occultation of
Aldebaran last night? At least two of us here at Weber State did--John
Sohl and myself. Neither John nor I ever recall seeing an occultation of
such a bright star, and it was a spectactular happening!

According to my clock, the occultation began at 10:45 p.m., MDT last
evening (Apr. 10). That is when the leading (i.e., dark) edge of the moon
went in front of the star. The crescent (3-day old) moon was still sufficiently
high above the horizon from Ogden, Utah, at the time, so it was easy to
see.

Some time ago the question was raised on the list about simple ways to
measure the size of the earth using the sun. This occultation can give a
way for students to estimate the speed, orbit radius, and size of the moon, if
we can get timing information from different parts of the country. There are
several motions occuring all at once, of course, and they would all have to
be factored into the calculation. The main effect is the orbital speed of the
moon--roughly its diameter every hour, or 2000 mi/hr. Then the rotation of
the earth--roughly 800 mi/hr at 41 degrees North latitude--is in the same
direction. So, the "shadow" of the moon only moves across the surface
about 1200 mi/hr or so. Anyway, we can figure all these things out if
anyone else can provide additional data points to go with the one above.

Let's hear it from anyone who witnessed last night's occultation. It should
have been easily visible from the west coast and all of the Mountain time
zone, maybe even into the western part of the Central time zone, though
the moon would have been pretty low there at the time of occultation.

Rondo Jeffery, Weber State University, Ogden, Utah
RJeffery@weber.edu