From Vice.com:
John Ford’s classic 1950 Western Rio Grande stars John Wayne as Lieutenant Colonel Kirby Yorke, whose regiment is tasked with defending settlers in Texas from Apaches during the late 1800s.
A little over an hour into the film, Kirby tells his wife that he’s decided not to bring Jefferson along with him in pursuit of the Apaches in Mexico. Though Rio Grande remains beloved for a great many reasons, this scene in particular has attracted considerable attention in recent years—and not for anything that was intended by the cast or crew. If you keep your eye on the top left-hand part of the screen as Kirby’s breaking the news to Kathleen, you’ll see what looks like a UFO shooting across the sky in the background. Check out the clip for yourself below.