I was reading the answers to this question:

What did the sky actually look like from the Moon?

And it got me thinking... What, if any, astronomy tasks could be performed better on the lunar far side than on Earth (or in general)? They mention that the albedo properties of the moon (when the light is shining upon it) are about as bad as Earth. Would there be any benefit from studying stars on the far side of the moon as compared to studying them from Earth? Have there been missions to the far side of the moon for such purposes or otherwise?

Please ignore thermal and energy limitations in your answer, assume a spacecraft that can deal with massive fluctuations of both temperature and light availability.

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    $\begingroup$ The Dark Side of the Moon is an album by Pink Floyd, and an album by Nichelle Nichols, and an album by Medicine Head, and something that mentions Henry Rollins, and a bunch of other things. But there is no such fixed "side" of the Moon that is dark except the poles to some extent. $\endgroup$ – uhoh Jun 29 '18 at 23:34
  • $\begingroup$ Vs Earth - huge; lack of atmosphere. Vs space telescopes like Hubble or JWST - about none, just a lot of big headaches. $\endgroup$ – SF. Jun 30 '18 at 6:27
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    $\begingroup$ The more accepted term the dark side of the Moon is the far side of the Moon $\endgroup$ – Fred Jun 30 '18 at 13:55
  • $\begingroup$ "Dark Side of the Moon" is also a great mockumentary about the moon landing hoax. See imdb.com/title/tt0344160 $\endgroup$ – hdhondt Jul 1 '18 at 23:46

The short answer: for optical astronomy (IR through gamma wavelengths), no, there isn't any huge advantage. But for radio astronomy there are distinct advantages to being on the lunar far side, they're just not related to any albedo differences.

Electrostatic forces loft tiny (micron-sized) dust particles above the moon's surface. When lit by sunlight they cause background light levels roughly comparable to those at good observing spots on Earth, so there's no advantage there. At night (which lasts about 14 Earth days) those dust particles are not lit, so there is the minor advantage of lower background light levels for optical observing.

That dust is the source of a distinct disadvantage: it can coat optics. And lunar dust isn't like Earth dust. It is hard, angular, and extremely abrasive, (same reference as above) so you can't just brush it off a mirror's surface—it would scratch the heck out of that surface!

For radio astronomers, especially those wanting to do radio astronomy at very low frequencies (tens of MHz and below), the far side of the moon would be the perfect place for observations (see this ESA PDF). Earth itself is a cacophony of radio signals at every frequency. For a Star Trek 4 analogy, for long-wavelength radio astronomers Earth is the guy on the bus with the blaring boom-box. The far side of the moon would shield against the great majority of that noise. And at night, when the sun (also a significant source of radio noise) is out of the sky, the radio environment is very quiet. Some scientists see that environment as such a unique resource that they propose to establish UN-managed radio-quiet zones on the lunar far side.

So far there haven't been any missions sent to land on the lunar far side. One good reason is that a lander there can't communicate with Earth unless there's a telecom relay spacecraft overhead and in view of Earth. You might do that with an orbiter in low lunar orbit, so you get brief telecom passes every couple of hours. Or you might put a relay spacecraft in a loose Lissajous orbit around the Earth-moon L2 point. Either way, this makes the mission much more expensive.

In its New Frontiers Program, NASA specifies that one of the missions eligible for consideration is the "Lunar South Pole Aitkin Basin" mission, which would involve a landing on the lunar far side. The proposal for the Moonrise mission that would have pursued that science was not selected in the last round of competition. It would not have addressed lunar sky brightness or dust lofting.

  • $\begingroup$ Really interesting answer! I've just asked How bright would electrostatically suspended dust above the lunar surface be? Has it ever been measured? $\endgroup$ – uhoh Jul 1 '18 at 7:04
  • $\begingroup$ Thank you! That is awesome, had no idea that the lunar dust would be such a problem for optics. Is there really no feasible way to remove lunar dust from a lens without scratching? And I'm reading about the radio isolation zones now :). $\endgroup$ – Magic Octopus Urn Jul 2 '18 at 13:03
  • $\begingroup$ @MagicOctopusUrn You might try blowing it off with a stream of gas, but I can think of problems even that would create. Instead of being dragged along the mirror surface, the particles could "saltate" (bounce along, blown by this artificial wind), and each impact on the mirror surface would make a tiny crater—sort of like sandblasting. Also, in a vacuum, a dusty gas flow like that can cause electrostatic charge to build up, so the mirror might attract even more charged dust particles. $\endgroup$ – Tom Spilker Jul 2 '18 at 19:40

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