Re: Crescent Moon Cusp Orientation
- From: brian@xxxxxxx (Brian Tung)
- Date: Tue, 28 Aug 2007 00:54:39 -0700 (PDT)
Bill Owen wrote:
The line joining the two cusps of the crescent moon is perpendicular to
the line from the moon to the sun. (When I write "line" here, it's
really a *plane* defined by the two points in question and the observer.
You-know-who will just have to get over it. Anyway....)
Or the great circle on the celestial sphere passing through both the Sun
and the Moon.
In order for
the lower cusp to be closer in azimuth to the sun than the upper cusp,
the sun must be higher in the sky than the moon. For a waxing crescent,
this geometry would occur in the *morning*, after moonrise, at all
latitudes.
Note that once the moon becomes gibbous, this conclusion no longer
holds. I'll let others explain why. :-)
I must confess I'm not sure what you're getting at. A gibbous Moon at
moonrise is still lower than the morning Sun. (Unless the Moon rises
first...but then, that can happen for a crescent as well as the gibbous
Moon.) I must be missing something.
--
Brian Tung <brian@xxxxxxx>
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