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(meteorobs) [IMO-News] Observing Lunar Geminids




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Date: Fri, 10 Dec 1999 11:07:53 -0500
To: occultation@skypub.com
From: Joan and David Dunham <dunham@erols.com>
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Subject: [IMO-News] Observing Lunar Geminids

    First, I apologize to those of you who don't have telescopes;
I must get this message out quickly and am therefore sending this
to my ENTIRE mailing list - if you are in this category,
just delete the message now.
_________________________________________________________________

    Much good information about observing lunar Geminids has already
been posted at http://www.LunarImpact.com NASA Science's Web site,
which you should visit.  Also useful is the diagram showing the
expected Geminid rates at
http://www.skypub.com/sights/meteors/geminids
Although it shows the situation for 1998, it gives solar longitudes
at the bottom that can be used to also determine the situation for
1999.  For 1999, the leftmost part of the chart (solar longitude
261.2 deg.) occurs at 16h U.T. of Dec. 13.  This indicates that
the best part of the shower, with rates of 100 or more per hour,
will occur from about 9h to 21h UT of Dec. 14.  Keeping in mind
that these are for the Earth, and that the Moon follows the
Earth around the Sun at this time by about 2 hours, it indicates
that observers in the Pacific Ocean region, Asia and Australia
should have the best chances for observing Geminids striking the
Moon.  But the rates will be about half the maximum or more for a 
longer time, from about 18h U.T. of Dec. 13 to 9h U.T. of Dec. 15,
so observers are encouraged to observe whenever the Moon is 
reasonably well-placed in a dark sky during this period, roughly
the evenings of Dec. 13th and 14th local time for most, including
the Americas.

     The LunarImpact site above lists bright stars near the Moon
that can be recorded briefly at the beginning of a taping for
calibration.  Also, a few 7th and 8th magnitude stars will be 
near the Moon at times; every 15 minutes or so examine the space
ahead of the dark limb to see if any stars are approaching it,
and record them if you see any, preferably up to the time of
their occultation.  Predictions for some of these events for
North America are given at IOTA's Web site at
http://www.lunar-occultations.com/iota

     Occultation observers and others with telescopes and 
video cameras are encouraged to try to record these events with
whatever equipment they have.  Even visual observers are not
discouraged, especially if they can time any flashes they might
see using a tape recorder or stopwatch and either shortwave
or accurate telephone (such as the USNO master clock) time
signals.  If Brian Cudnik had not observed visually on Nov. 18th,
we might still not know about the lunar Leonids, since most of
us would not have looked at our lunar tapes closely until
well afterwards, or in some cases, if ever.

     Video observers should also try to take precautions so
that any flashes that they observe might be located on the 
Moon's surface, to compare with others to rule out for sure
the possibility of a sunglint from a very high-altitude
satellite.  Keep your camera at the same orientation and
at the start of an observing run, record a little of the
north and south cusps, and terminator.  Then during the
observation, try to keep part of the dark edge of the Moon
in view.  The dark side was hard to detect in most videos
on Nov. 18th with the Moon over 60% sunlit, but for the
Geminids, the Earthshine will be brighter and glare from
the sunlit side less, so most telescopic video systems 
should pick it up.

     The Geminids will strike the Moon with less velocity
than the Leonids, so their flashes will probably not be
as bright.  Also, the density of objects is lower.  
Nevertheless, I think it is worth a concerted effort to
see what might happen.  The Geminid rates raise relatively
slowly to the broad peak, then fall more rapidly.  However,
I've heard that the later meteors (those on the evening of
the 14th local time) tend to be brighter (larger), so
that might produce more observable flashes on the Moon.

     David Dunham, IOTA, 1999 December 10o
Joan and David Dunham
7006 Megan Lane
Greenbelt, MD 20770
(301) 474-4722
dunham@erols.com

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