Re: Paint the Moon

[David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>]

Regarding my previous post where I wrote:

> ...  Since the Moon subtends about
> 1/2 deg, this means that the aiming needs to be accurate to within
> about 1/20 deg (or 3 arc min).

I just did a very crude experiment with my cheapo Radio Shack laser
pointer.  I measured the diameter of the brightest part of the spot
when it shined on a whiteboard while it was held in a ring stand at
8 m away.  It seems the spot is approximately elliptical with a
major diameter of about 0.05 deg and a minor diameter of about
0.025 deg.  The major diameter seems to be just approximately the
size of the target spot size described at the www.paintthemoon.org
web site.  Thus the aiming only needs to be accurate and steady to
within about the spot size itself if most of the laser pointers
have a beam spread comparable to mine.

For some reason I doubt that most of the people using their
pointers for the project will go to the lengths necessary to keep
their pointers pointing accurately on the intended target area.

Also there don't seem to be anywhere near enough laser pointers in
the whole Earth to be able to cause sufficient illumination for a
spot to be visible on Earth even if by some miracle they *were* all
pointing to the same target area concurrently.

David Bowman
David_Bowman@georgetowncollege.edu