[Bring_Back_Shantz]

Originally Posted by PsYcNeT

Not entirely true.

The biggest deterrances to observing other planets in any sort of general detail (other than ones so far away we can only see gravitational or radio proof of their existance) is a) clouds (on earth and on their planets), b) reflected light, c) atmospheric interference.

All 3 of these can be negated by having a telescope in space (see: the hubble) but a sattelite telescope can only be so powerful. Having the ability to establish a full sized (optical) telescope (something like the LBT) on the moons surface would give us much greater optical detail into say, what's going on on Jupiter, but it sure as hell wouldn't let us see past all it's atmospheric gases/dust.

Okay, I thought you were talking about planets out of our solar system.
You said "Planets we can't reach", and we can reach all of the ones in our solar system, so I assumed you were talking about others.

Either way, I'm not sure what your point is about a moon observatory.
There's no way you could build something large enough to physically see extrasolar planets, and it still has no bearing on seeing say the surface of Venus.