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RE: (meteorobs) Excerpts from "CCNet DIGEST, 15 June 1999
> (10) WATCHING METEORITES FALL ON THE MOON
>
> 1) Would it be best to use a low power eyepiece and fill the field of view
> with the unlit portion of the Moon, or use higher powers and view smaller
> areas?
In general, a stellar image is best seen against the 'sky' background by
using a higher power. A stellar flash would be expected rather than a
diffuse cloud rising into sunlight. A coordinated group of observers
looking at the unlit portion at high powers, would maximise the chance of
success.
> 2) Considering the geometry of Earth-Moon-Leonid stream that evening, is
> there some area of the "visible" unlit portion of the moon likely to
> experience more meteor impacts per unit surface area than the remainder of
> the "visible" unlit portion?
The angle from the lunar limb to the "Leonid terminator" is equal to the
elongation of the Moon from the Leonid apparent radiant. You could
call this the "Leonid phase of the Moon". Thus, Leonid impacts could only
be visible on the unlit portion of the Moon for those phases that have
some unlit portion pointing towards the Leonid radiant. The part of the
visible Moon closest to the radiant will have the greatest number of
impacts per unit lunar surface area, and as this is on the lunar limb as
seen from the Earth, the apparent area is also strongly compressed. But
despite the dramatic increase in impacts towards this limb region, the
problem with this is that rough terrain near the limb will shield the
impacts from direct line of sight. It would seem that any Mare close to
the part of the lunar limb pointed towards the leonid radiant, would give
the best chance of seeing anything. The maths of the relative impact
frequency for any specific part of the lunar surface as seen from the
Earth would appear to be proportional to
sin(elev)dot sin(ang)
where
elev is the elevation of the Leonid radiant from that point on the Moon
and
ang is the angle of that position from the center of the apparent lunar
disk
Cheers, Rob
Robert H. McNaught
rmn@aaocbn.aaodot gov.au
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