Some famous UFOs -- or were they?

LONDON (Reuters) - Here are some of the more celebrated UFO sightings:

MOUNT RAINIER, WASHINGTON

May 1947 - In the first sighting since World War Two -- during which there had been several reports of "foo fighters" or balls of light following combat aircraft -- American businessman Kenneth Arnold saw lights in the sky near Mount Rainier, in the northwest United States.

He described seeing nine silvery objects that flew erratically, "like a saucer skipping across the water". Newspapers seized on his account and a new phrase entered the language - "flying saucer".

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ROSWELL, NEW MEXICO

July 1947 - The daddy of them all, the Roswell incident in which an alien craft was widely believed to have crashed.

According to some accounts, the ship crashed in an empty field with several aliens on board. Those who believe an alien craft landed are adamant the incident involves a huge government cover-up.

The official explanation was that it was a secret research balloon that had come down.

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KECKSBURG, PENNSLYVANIA

In December 1965, residents of Kecksburg watched a fireball crash into a heavily forested area 40 miles from Pittsburgh.

That night, the area was cordoned off by the military. Trucks and helicopters came and went, and the town was reportedly placed under martial law for a short time.

Reports say a truck took away an acorn-shaped object about the size of a VW Beetle.

The official explanation: a meteor strike.

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