On 24 June 1947 Kenneth Arnold, a businessman and pilot, was flying along the Cascades when he saw nine objects strung out near the slope of Mount Rainier, moving at enormous speed. On landing he described their motion to a reporter: like a saucer skipped across water. The paper shortened that to "flying saucers", and the phrase has existed ever since. Arnold himself insisted the objects were not round but crescent-shaped, and that the press had described the movement rather than the shape. Nobody heard the correction. The sighting is generally taken as the start of the whole modern subject: before it, reports of strange things in the sky were occasional; after it, they came in floods.

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The Berwyns and the Welsh Roswell

On the evening of 23 January 1974 the ground shook in the Berwyn mountains of north Wales and lights were seen on the hillside. People assumed an aircraft had come down; police, a nurse and mountain rescue climbed in the dark and found nothing. Over the years the story acquired military lorries carrying containers away, and the nickname the Welsh Roswell. Seismic records show a real earthquake of about magnitude 3.5 that evening, and the lights fit well with a bright fireball seen across northern Britain in the same minutes. The coincidence of two events in one evening produced everything else.