I'm just a bridge engineer and amateur astronomer, so I'm hoping someone here with more advanced expertise in light waves and reflective surfaces can help me. Basically I was wondering how big a space telescope's primary mirror would have to be in order to view an exoplanet 10 or so light years away with the same resolution as the images of Earth taken from the moon. Obviously, it would have to be massive, like a kilometer or so in diameter, which I believe is possible given today's technology but impractical given how much it would cost to lift all of those mirrors into place. So, I came up with an idea that is probably totally absurd, but I'm just going to bounce it off you guys. The idea I have is to create what is basically a kilometer wide primary mirror with 99% or so of it missing. What I mean is, you would have two or four very slender arms (maybe as small as one degree, if you think of a 360 degree circle) where the mirrors are, and in order to generate a complete picture you have to rotate the entire telescope such that the arms "carve out" a complete 360 degree picture. To help illustrate, here's a very rough sketch I drew up showing the primary mirror: http://s8.postimg.org/47eold9et/telescope.jpg The purpose, of course, is to cut down on the overall mass and weight of the telescope, such that it would be more affordable to lift into place. The thing I'm wondering though is, is it even physically possible for light to be captured and properly reflected this way? I'm thinking that if such a telescope were to zero in on a distant Earth-like exoplanet and snap one picture, it might look like this: http://s9.postimg.org/8wps3d9rz/earth.jpg Then, the telescope (or at least the primary mirror) would be rotated a few degrees, another picture would be taken, rotated again, another picture taken, and the process is repeated until an entire 360 degree picture can be stitched together. But, would light behave in such a way, or would it just be a blurry blob? Does it need a complete 360 degree mirror? I know there would still be other astronomical costs such as a kilometer wide sun shield, and it would require a lot of energy to rotate such massive arms, but right now I'm just wondering if it's physically possible, and whether or not light would behave in such a way.