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THE ASTRONOMER Electronic Circular No 1884      2003 May 14 19.43UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK             GMH at AST.STAR.RL.AC.UK
WORLD WIDE WEB                         http://www.theastronomer.org
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LUNAR ECLIPSE, 2003 May 15/16
Richard Keen e-mails:
Since many of you have kindly sent me observations of one or more
of the lunar eclipses in 2000 and 2001, you probably know what this
message is about!  Your observations were quite helpful in my
research, and you may wish to read the report in the May, 2001,
issue of the "Bulletin of the Global Volcanism Network."  The GVN
web site is:     http://www.volcano.si.edu/gvp/
Check the May, 2001, and look for "Atmospheric effects".  You'll
even find an acknowledgement of your efforts!

Here's a repeat of a "request of observations", this time for the
eclipses of May 16 and November 9.....
I am writing to request such observations of the brightness of the
moon during the total lunar eclipse. The brightness of the moon
during a total lunar eclipse is extremely sensitive to the presence
of volcanic dust in the earth's atmosphere. As part of a continuing
research project, I have used observed lunar eclipse brightnesses
to calculate a history of optical thicknesses of volcanic dust
layers (R. Keen, "Volcanic Aerosols and Lunar Eclipses", Science,
222, pages 1011-1013, 1983; Sky & Telescope, June 1984, page 512).
The resulting optical thicknesses are useful to climatologists (for
volcano-climate studies) and to volcanologists (for estimating
total amount of material ejected by an eruption).

Here's a brief description of one way to measure the brightness of
a lunar eclipse: 

The totally eclipsed moon is usually brighter than most comparison
stars (I expect about magnitude -3 at second and third contacts,
and -1.4 at mid-totality, assuming no volcanic dust present), and
its brightness needs to be reduced before a direct comparison can
be made.  An easy way to do this is to view the moon through
reversed binoculars with one eye, comparing the reduced lunar image
with stars seen directly with the other eye. The estimated
magnitude of the reduced moon can be adjusted by a factor depending
on the magnification of the binoculars, yielding the actual
magnitude of the moon.  For example, reversed 10x50 binoculars will
reduce the apparent diameter of the moon by a factor of 10, or its
brightness by a factor of 100, or 5 magnitudes.  If the reduced
moon appears like a magnitude 3 star, the actual moon is 5
magnitudes brighter, or -2.  The corrections for 8x, 7x, and 6x
binoculars are 4.5, 4.2, and 3.9 magnitudes, respectively. These
correction factors assume the stated magnification of the
binoculars is correct, and neglects light loss in the optics. More
accurate correction factors can be empirically derived from
observations of Venus, Jupiter, or Sirius. 

Observations made from the beginning to end of totality will reveal
the darkening of the moon as it slips deeper into the umbra, but
the most useful observations (for measuring volcanic dust) are
those taken near mid-totality. 

I am also interested in any and all brightness observations of past
or future lunar eclipses. Any reports of Danjon L-scale values will
help me compute brightnesses of older eclipses for which only L-
values are available.  Reports should include time(s) of
observation, size of binoculars (or other method) used, and
identity of comparison stars or planets.

Editor: Please send your reports to Mark Kidger, TA planetary
editor who will collate and liaise with Richard as necessary. Mark
also encourages crater timings by more experienced observers.

Guy M Hurst