A lens bends the path light takes (this is called
refraction), so that a photon that would otherwise miss your camera gets directed into it. Again with a rain analogy: A raindrop that falls a meter away from you misses you, but if you could deflect (refract!) the path of that drop a little bit while it s still up high, it ll be aimed right at you, and you get wet.
In the case of the Terrascope, the lens is actually Earth s atmosphere. When light moves from one medium to another (like air to water, or space to air), its path bends a little bit. The amount it bends depends on the angle it enters and the stuff (what we usually call the
Subsurface oceans on alien worlds even better for life than Earth s oceans? | Space earthsky.org - get the latest breaking news, showbiz & celebrity photos, sport news & rumours, viral videos and top stories from earthsky.org Daily Mail and Mail on Sunday newspapers.