The Apollo 16 Incident

When the Apollo 16 mission was preparing to return back from the Moon on April 27, 1972  ....

The Apollo 16 Images That Sparked The Debate ......

.... from a command/service module window they filmed about four seconds of video footage, of an object that looked like a UFO.

Mysterious Explanations

There are lots of 'mystery' websites on the web, which I find highly entertaining. These usually try to pass certain well known stories or images off as being 'unexplained mysteries', or in some cases proof positive of Aliens / NASA Cover ups / Bigfoot / Conspiracy theories of all sorts etc etc etc.

1964 - Templeton Spaceman Solway Firth UK

They often give you some sort of 'facts' relating to the image or story, which will give you enough to ensure that a cursory investigation appears to prove that this is all a genuine mystery. However, dig a little deeper and the 'mystery' often rapidly disappears. 
 
Perhaps one of the oldest out there, and therefore most often used, is the so called Solway Spaceman ...