Given the current brouhaha in Congress over immigration reform, it’s easy to forget that on this day 58 years ago, Washingtonians were worried about illegal aliens of a different sort. This declassified Air Force report describes the sighting of a UFO hovering over the Pentagon on the evening of July 27, 1952. The witness, a woman from Arlington, VA, reportedly observed a bright white light that lingered over the Department of Defense, made a descent toward it, and then abruptly took off. It actually was the second UFO sighting of the evening — the same object, or a similar one, reportedly appeared over the U.S. capitol at about 7:30 p.m., according to a chronology of sightings compiled by the National Investigations Committee on Aerial Phenomena, a private-sector UFOlogy group. It was never determined whether the sighting was actually a spacecraft, or merely an illusion caused by random emissions of swamp gas from a Congressional debate. But while you’re waiting for the Men in Black to show up and erase your memory of reading this article, here are the science stories of the day.