The Phoenix Lights (sometimes referred to as the lights over Phoenix) were a series of widely sighted optical phenomena (generally unidentified flying objects) that occurred in the skies over the U.S. states of Arizona and Nevada, and the Mexican state of Sonora on March 13, 1997. A repeat of the lights occurred February 6, 2007, and was filmed by the local Fox News TV station.
A similar incident occurred April 21, 2008. This incident was later revealed to be prank–flares attached to helium balloons.
Lights of varying descriptions were seen by thousands of people between 19:30 and 22:30 MST, in a space of about 300 miles, from the Nevada line, through Phoenix, to the edge of Tucson. There were two distinct events involved in the incident: a triangular formation of lights seen to pass over the state, and a series of stationary lights seen in the Phoenix area.
The United States Air Force (USAF) identified the second group of lights as flares dropped by A-10 Warthog aircraft which were on training exercises at the Barry Goldwater Range in southwest Arizona. Witnesses claim to have observed a huge carpenter's square-shaped UFO, containing lights or possibly light-emitting engines. Fife Symington, the governor at the time, was one witness to this incident. (Excerpt from en.wikipedia.org)