John Kelly, Columnist

This month marks the 60th anniversary of the Great Alien Invasion of 1952 or, as it might more appropriately be called, the Great Alien Reconnaissance of 1952. The UFOs allegedly just flew around; no one saw them land.

But were they aliens? This much is undisputed: Late on the evening of July 19, 1952, air traffic controllers at Washington National Airport spotted a curious cluster of seven blips on their radar screens. Similar blips were sighted by radar operators at Andrews and Bolling Air Force bases.

National’s control tower contacted commercial aircraft in the vicinity and asked their pilots if they had seen anything unusual. Why yes, Capt. S.C. “Casey” Pierman of Capital Air Flight 807 radioed back. He saw six bright lights streaking across the sky, “like falling stars without tails.”

F-94 jets were scrambled from Delaware’s New Castle Air Force Base (the runway at Andrews was under repair), but the pilots saw nothing.

The Pentagon was already studying the escalating number of UFO sightings — under the aegis of Project Blue Book — and the officer in charge added the Washington outbreak to his growing list. Then, the next weekend, it happened all over again. National Airport’s air traffic controllers tracked a dozen unexplained blips.

Fighter jets were again scrambled, and on their second circuit, pilots saw bright lights speeding away from them.

“I tried to make contact with the bogies below 1,000 feet,” pilot William Patterson later told investigators. “I was at my maximum speed but . . . I ceased chasing them because I saw no chance of overtaking them.”

The media had a field day. A headline on the front page of The Washington Post read: “ ‘Saucer’ Outran Jet, Pilot Says; Air Force Puts Lid on Inquiry.”

After the earlier outbreak, a reporter for the Washington Daily News had written: “Recent attempts to explain ‘saucers’ as optical illusions have been shaken by recent radar sightings. Illusions don’t show up on a radar screen.”

Illusions don’t, but temperature inversions do. A temperature inversion occurs when a layer of cold air is trapped under a layer of warm air. It’s most common in extremely hot weather of the sort that Washington was enduring 60 summers ago. The warm air can create a ceiling that causes radar beams to bounce down.

Objects on the ground — moving cars, a row of telephone poles — can appear to be thousands of feet in the air. An Air Force officer ascribed the sightings to this phenomenon.

But what of the lights? A layer of moisture in the atmosphere could have caused reflections.

“It’s very much like when you’re riding down the highway and it’s very hot out and you see a mirage on the highway,” said Bruce Press of National Capital Area Skeptics, a group that debunks UFOs, ghosts and the like. “As you drive towards it it doesn’t get any closer, so you assume that because it doesn’t get any closer it’s moving away from you at the same speed you’re driving.”

UFOlogists discount these explanations. Experienced pilots saw the lights, said Robert Swiatek of the Mutual UFO Network, and National’s radar operators felt that “the anomalous signals were good, solid targets, as though they were being reflected from the surface of metallic aircraft.”

While there certainly are more things in heaven and earth than are dreamt of in Answer Man’s philosophy, he must side with the skeptics in what became known as the “Washington Flap.” Even before that hot July, the papers were full of stories about UFOs.

They were a staple of science-fiction movies in an America fearful of a Soviet invasion.