Tuesday marks the 21st anniversary of the so-called "Phoenix Lights" that appeared along the Valley's skyline on March 13, 1997.
Some believe it was a visit from life outside of this world. Skeptics acknowledge the formation of orange and red lights that appeared, but they're unable to explain what it was.
"It's the most witnessed, the most documented, most important mass anomaly sighting," said Phoenix Lights documentary director, writer and producer Dr. Lynne Kitei.
On Sunday, there will be a documentary screening, followed by a Q&A session with researchers and witnesses. Organizers say this will allow people to ask the questions they may have been too afraid to bring up before.
"I think folks can be defamed," said Dr. Bob Evans.
Evans told ABC15 that he witnessed the lights while traveling to Phoenix from Tucson with his family that March night.
His wife the first one to spot something strange in the sky.
"And she pointed to about the 1 o'clock position...right in that corridor," Evans gestured with his hand. "And said, 'Well, then what is that?'"
However, he has never spoken publicly about it. He was worried about it hurting his medical career with what he describes as, the "UFO stigma."
But, now that he has retired and has spent time talking to advocates like Dr. Kitei he is excited to be apart of the event.
"I don't care if there are 2 or 270 [people]," Evans said. "They're showing up for a reason. I want to know why they're showing up now."
IF YOU GO:
Harkins Theatres Scottsdale Shea 14
7354 E Shea Boulevard
Scottsdale, AZ 85260