Tacoma, WashingtonAugust 1956

On the evening of August 18, 1956, a resident of Tacoma, Washington reported watching a round object about the size of a dime held at arm's length. The object alternated between blue and white light, with the brightness increasing and decreasing as it moved across the sky. The observer watched it travel from east to west, at one point stopping in the middle of the sky before continuing westward. The object appeared small enough to form a triangle when lined up with two nearby stars, and the witness reported it was moving at a high rate of speed.

The Air Force's investigation noted several details from the report. The object started at a low elevation in the eastern sky and climbed higher as it moved. At its highest point, it was observed at 55 degrees elevation (roughly halfway up from horizon to zenith). Weather data from the time showed a temperature inversion existed, a layer of warm air sandwiched between cooler air both above and below it. These inversions can bend light and create optical illusions.

The Air Force evaluated the sighting as probably astronomical in nature, specifically suggesting the bright star Deneb as a likely explanation. The case file notes that the observer's initial report of a high rate of speed could not be confirmed, and that viewing conditions through the temperature inversion may have distorted the object's appearance and motion. The full case file, consisting of 15 pages as held by the National Archives, is reproduced below.