[AZ-Observing] Re: Two crescents
- From: Gene A Lucas <geneluca@xxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Wed, 22 Apr 2009 17:08:59 -0700
I got up early <yawn> and set up my Meade 4 inch f:10 SCT on my new
CubePro alt-az mount, right on my balcony here in Fountain Hills,
elevation 1900 ft overlooking the Four Peaks range to the east. The
CubePro was set up and ready in a jiffy, which made it all easy with its
built-in GPS.
With an 11mm Brandon eyepiece, I watched Venus slide behind the lunar
crescent, and noted the brilliant white color. Contrary to Steve's
observation, I estimated it took about 45 seconds (counting them off by
hand) for the crescent parts to be covered by the Moon's motion -- could
not see the dark part of the ball of Venus, of course. The two "horns"
just touched the lunar limb together at the start, as seen from here in
FH... There could be a considerable difference in the angle that Venus
approached the Moon, from two widely-separated observing locations, of
course, which would produce a difference in timing.
I, too, noted the effect of the white Venus crescent appearing to
slightly overlap the Moon's surface -- the technical term is
"irradiance" and it is evidently caused by the contrast and brilliance
of the image. This effect is also contributed to by scintillation and
seeing variations. This effect has also been noted sometimes in the
case of Supergiant stars during lunar occultations.
I did not stay up to observe the egress from behind the Moon... I lost
the Moon in the sunrise sky, but that may also have been due to a
Jacaranda tree that is in the way... Perfectly clear skies this morning...
I left the photography and videography to others this time...
Gene Lucas
(17250)
As usual, I just copied Rick and Steve's earlier, longish memos on the
end of mine, and got bit (again) by The Dreaded Net Nanny....
What a stupid limitation, IMHO !!
GL
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