Re: Can any man-made object be seen on the moon from earth?

I've certainly never heard of any such observations, but that doesn't prove that they don't exist. So I decided to figure out how large a telescope one would need to see a moon lander. The angular size (how big it appears to be) goes like (206,265) * (size)/(distance), while the smallest thing you can see with a telescope goes like (0.25) * (wavelenth of the light)/(diameter of the telescope) [Note: wavelength is measured in microns, or one-millionths of a meter]. I estimated that the landers were maybe 10 meters across and figured 0.6 microns for the wavelength (this is about right for red light). The distance to the moon is 284,400 km, so playing around with the algebra and solving, I got that you'd want a telescope at least 28 meters across. Unfortunately, this is well larger than any (optical) telescope ever built.

Even if such a telescope existed, at this small size you'd have trouble seeing through the atmosphere. Additionally, most large telescopes won't or can't look in the moon's direction because they will, in essence, be blinded by the brightness (Hubble, for example, shuts down and has to be coaxed back into operation if anyone tries to point it at the moon, Earth or the sun).

To leave off on a brighter note, people have imaged things in orbit about the Earth, being much closer. Amateur astronomers, typically with 8" to 16" diameter telescopes have taken some remarkably clear pictures of the space shuttles and Mir (sometimes together). The fact that these objects are many times closer than the moon is what allows them to do take this stunning (and terribly cool) pictures.

If you want to learn more about angular size and resolution of telescopes (i.e. - what's the smallest thing that they can see?), I'd suggest a good introductory astronomy text, since most of them have really good discussion of this material without going crazy with the detailed physics. I personally would suggest Astronomy Today by Chaisson and McMillian, but you're welcomed to choose a different one!