New Close-Ups of Saturn's Geyser Moon

I wonder how good a telescope we would need to actually see a human being on the surface of the moon anyway?

It would have to be very good. For example, the Hubble space telescope couldn't do it. Not even close. (Despite the fact that it can image galaxies that are billions of light-years away.)

Let's say that seeing an astronaut convincingly requires a resolution of ~5 cm (at that resolution, their hand would be a bit of a blob, but at least you'd be able to tell that it was a person and not a rover...). Let's assume we're using the violet-end of the visible spectrum (wavelength lambda ~ 400 nm). Using the resolution equation [wikipedia.org]:
sin(theta) = 1.22 * lambda/D

theta is the angular difference we're interested in, D is the size of the aperture/optical system, the 1.22 factor can vary a bit between optical schemes but is close enough for our purposes. The distance to the moon is 384,000 km [wikipedia.org], so the angle theta is [google.com] arctan(5 cm/384000 km) = 7.5E-9 degrees. So [google.com]:
D = (1.22 * 400 nm)/( sin(7.5E-9 degrees) ) = 3.7 km

So, we would need an optical telescope with an aperture/mirror that is 3.7 km in diameter. Needless to say, this is quite a bit bigger than any telescope that exists today (the best is about 12 m [wikipedia.org]). If you want to be able to accurately see the astronaut's eyes, to confirm that he's really not a robot, then the telescope would have to be even bigger (like 40 km in diameter).

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/IRkbaOcng0Y/New-Close-Ups-of-Saturns-Geyser-Moon

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