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Really ignorant question: some comments mention huge telescopes: can a moon be used via gravitational lens-ing to effect a huge telescope?

• sandworm101 4y ago
  No. The focal point would be so far away, as in way bigger that the moon's orbit, that the entire arrangement would be wildly impractical. Imagine hanging out around pluto's orbit while trying to aim at earths moon as it spins around the earth. Using the earth would be easier. Using jupiter would be easier. It is possible to build a refracting telescope in space that uses earths atmosphere as a lens. This is far more practical (ie smaller) than any gravity telescope.
  • tadfisher 4y ago
    The sun's focal point is 542 AU, about 11 times Pluto's orbit. It's safe to say we won't be using Jupiter or Earth as lenses anytime soon.
    • sandworm101 4y ago
      Not as gravity lenses, but as both planets have atmospheres they can be used as refracting lenses at much shorter focal points at orbits, if using earth, just beyond the moon. https://www.science20.com/tommaso_dorigo/the_terrascope_using_earth_as_a_lens-240567 https://www.science20.com/tommaso_dorigo/the_terrascope_usin...
    • flangola7 4y ago
      Could we start with Earth and scale up to the sun?
• tadfisher 4y ago
  The lens effect from something less massive than a star is too weak. The Sun has a focal point 542 AU away from its center; our moon would have a focal point some orders of magnitude beyond that, and the angular resolution wouldn't be nearly as good. In short, it's far easier and more effective to use the Sun for this effect. Radio interferometry would be a better use for Moon-based observatories, if we felt like building several of them.