NavList:

Hi Frank:

There are optical retro reflectors on the moon used with lasers to range the moon.  There are also a number of satellites with retro reflectors.
By feeding the laser into the eyepiece of a telescope you can expand the beam.  The expanded bean has a lower divergence.  I think the scopes used for this purpose are about 1 meter in diameter but the laser is an industrial high power unit.  This is one of the ways that the Earth's rotation is measured.

Have Fun,

Brooke Clarke, N6GCE
http://www.PRC68.com
Frank Reed wrote:

Ted G wrote:
"Geoffrey Kolbe's idea seem interesting although I for one would have thought
lunar occulation might just have been an easier method of determining
longitude in ancient times if based on hindsight; i.e.comparing data on
returning to base. "

Lunar occultations are much more difficult to use because the Moon is so close to the Earth (in navigator's lingo, because of the Moon's horizontal parallax). In a lunar eclipse, all observers who are able to see the Moon see the same things happening simultaneously. If two observers separated by thousands of miles chat on the phone during a lunar eclipse, they will be describing exactly the same scene on the face of the Moon. The Moon will appear in a different part of the sky, since they don't share local time, but the events on the Moon's face will be simultaneous. Contrast that situation with an occultation. If we chat on the phone while the Moon is getting ready to occult Aldebaran, I may yell out "it's gone! Aldebaran has been occulted", while you can still see it for many minutes later. We could later reduce those observations to geocentric timings, but it's a lot of extra calculation and it would not have been useful until the early 18th century when the lunar models were beginning to be really accurate.

A few years ago, some well-meaning but scientifically ignorant soul proposed a "laser the moon" day. He wanted everyone to point their pocket laser pointers at the Moon at the same time so that we could all see a little glowing patch of light on the Moon and partipicate in a cosmic experience. He and many other people who read about this did not understand that laser beams do, in fact, spread out with distance. So this project cannot work. But if you could do this... if you could "snap on" a light on the surface of the Moon at one instant of time, it would be the perfect longitude solution. Oh, no wait, GPS is the perfect longitude solution <g>, but you know what I mean...

Frank R
[X] Mystic, Connecticut
[ ] Chicago, Illinois