A couple of years ago astronomers trained the Hubble Space Telescope on a fairly empty patch of sky and left it there for ten days, trying to catch whatever photons straggled in. (discovermagazine.com)
If they encounter too many empty patches, they starve, and by the end of the level it's game over. (sciencedaily.com)
Penn Cove Shellfish and the UW researchers joined forces after company harvesters saw empty patches on some cultivation ropes that should have had mussels. (scientificamerican.com)