Arizona residents had a close encounter of the unusual kind on a warm spring night back more than 27 years ago.

On March 13, 1997, two formations of light were sighted in the skies over the Valley and other parts of Arizona. One was shaped like V and cruised across the sky while the other was a series of glowing orbs that appeared in a line near the Sierra Estrella mountain range.

The two incidents became known as the Phoenix Lights, one of the largest and best-known UFO sightings in history. Thousands of people across Arizona witnessed the phenomena, which caused a hullabaloo in the media over the next few months that grew into a worldwide obsession.

Despite the public clamoring for answers about what caused the Phoenix Lights, both at the time and over the ensuing decades, no official investigation has ever occurred. Here's everything to know about the Phoenix Lights.

"Everything to know?"  We certainly know what we don't know.

To read more, click here.