[Laser] How much power? Ideed!

[Art]

You wouldn't see a laser based on the Moon. Although the laser is 
collimated, the few (at best) photons that arrived on Earth would be 
masked by the Moon's reflectivity of the sun (light that bounces off 
the Moon and makes it's way to Earth).

The only hope of seeing a laser on the Moon (from the Earth) would 
happen only if the laser was located on the dark side of the 
terminator. In such a case, the field of view would have to be very 
narrow, about the same as the divergence of the laser transmitter, or 
around 2 to 5 milliradians. It would be just as difficult to aim 
receiver as it would be to aim the laser. When you consider that both 
the Moon and the Earth move relative to each other, both ends would 
need to be actively tracking each other.

I think receiving a laser based on the Moon would be difficult and a 
2 way QSO between the Moon and the Earth would ne next to impossible 
for amateurs.

Receiving an Earth based laser from the Moon would be even worse, the 
Earth is a much better reflector than the Moon is, so the background 
ambient light level would be much worse.






>If there
>were a Moon Base or just a rover up there with the equivalent of a
>laser pointer, 5 mW and 1.5 mR beamwidth, it could send a spot down that
>would be 360 miles across. How much of a telescope would you need to see
>that?