Video uploaded to YouTube appears to show a dark disc-shaped object loom into view across a close-up of the cratered lunar surface.
The object was said to be seen on December 3 during a live stream video from the Miami Observatory in Florida.
It has been picked up by UFO websites, which are convinced it could be evidence of an alien craft.
Scott C Waring posted on UFOsightingsdaily.com: “Caught on live video feed on telescope at an observatory in Miami, Florida, this dark UFO makes quite the impression.
“It’s not a man-made object, because there are not solar panel wings on it to gather energy.
“There are no antennas on it for transmitting.
“Also the surface is not completely round, but has a rough edge to it. Looks like a biomechanically grown UFO.”
Mr Waring did not explain what a biomechanically grown UFO was in his post or his evidence for it being one.
Dean Howe posted on YouTube: “Any idea what it could be? Other than aliens.”
Michael Clottey said: “Great stuff. Peekaboo UFO, they know we are watching.”