-------------------------------------------------------------------
THE ASTRONOMER Electronic Circular No 1064      1996 Apr 01 17.47UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK             GMH at AST.STAR.RL.AC.UK
WORLD WIDE WEB                    http://www.demon.co.uk/astronomer
-------------------------------------------------------------------
TOTAL LUNAR ECLIPSE
Observers are reminded that the total lunar eclipse of 1996 Apr 3/4
provides a possible opportunity to study Comet C/1996 B2 Hyakutake
under darker skies.

We have also received the following appeal for brightness estimates
of the eclipse from Richard Keen in USA:
No doubt you're all enjoying the flyby of Comet Hyakutake, and
using novel methods to observe a comet that bright, that close,
and that huge!  Some of these observing techniques can also be
applied to measuring the brightness of the moon during a total
lunar eclipse, and I am writing to request such observations.
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).
Since the 3-4 April total lunar eclipse is not visible from
Colorado I am requesting your help.  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.

Please send reports and feedback via the TA Editor

Guy M Hurst