Within our current knowledge, what is the largest (circular, say) area in the sky which is empty/dark? I'm thinking in terms of angular size.
I was wondering what was the largest star as seen from the Earth, other than the Sun of course, in terms of milliarcseconds, say. A search quickly turned up R Doradus which is huge (57 mas as seen from the Earth). But I wondered if it was possible to rule out any (angularly) larger dark objects by finding stars whose light would be blocked if there was such an object.
Of course we should eventually be able to rule out each such area -- as Hubble Deep Field showed, if you look long enough there's a lot to find everywhere -- but relative to our current knowledge, what are the largest gaps?
I expect that the answer would be in a region which has been missed by a sky survey and which coincidentally doesn't have anything we can see.