Quote:
Originally Posted by munin
How large does the size-to-distance ratio have to be before the obscuring or lensing of background stars are useful ways to detect objects?
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Well, in principle at least not any larger than the background star, but you've got to be lucky enough to have it actually cross in front of one while you're watching.
One could figure out how big it has to be before it usually
will obscure some, but I'm not going to try that now.