Kenneth Arnold unidentified flying object sighting

The Kenneth Arnold UFO sighting occurred on June 24, 1947, when private pilot Kenneth Arnold claimed that he saw a string of nine, shiny unidentified flying objects flying past Mount Rainier at speeds that Arnold estimated at a minimum of 1,200 miles an hour (1,932 km/hr). This was the first post-War sighting in the United States that garnered nationwide news coverage and is credited with being the first of the modern era of UFO sightings, including numerous reported sightings over the next two to three weeks. Arnold's description of the objects also led to the press quickly coining the terms flying saucer and flying disc as popular descriptive terms for UFOs.

On June 24, 1947, Arnold was flying from Chehalis, Washington to Yakima, Washington in a CallAir A-2 on a business trip. He made a brief detour after learning of a $5,000 reward for the discovery of a U.S. Marine Corps C-46 transport airplane that had crashed near Mt. Rainier. The skies were completely clear and there was a mild wind.

A few minutes before 3:00 p.m. at about 9,200 feet (2,800 m) in altitude and near Mineral, Washington, he gave up his search and started heading eastward towards Yakima. He saw a bright flashing light, similar to sunlight reflecting from a mirror. Afraid he might be dangerously close to another aircraft, Arnold scanned the skies around him, but all he could see was a DC-4 to his left and behind him, about 15 miles (24 km) away.

About 30 seconds after seeing the first flash of light, Arnold saw a series of bright flashes in the distance off to his left, or north of Mt. Rainier, which was then 20 to 25 miles (40 km) away. He thought they might be reflections on his airplane's windows, but a few quick tests (rocking his airplane from side to side, removing his eyeglasses, later rolling down his side window) ruled this out. The reflections came from flying objects. They flew in a long chain, and Arnold for a moment considered they might be a flock of geese, but quickly ruled this out for a number of reasons, including the altitude, bright glint, and obviously very fast speed. He then thought they might be a new type of jet and started looking intently for a tail and was surprised that he couldn't find any.

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Wikipedia