The man, who remains anonymous, called police from his home in Stevenage, Hertfordshire, to tell them he could see a brightly-lit UFO with a hole in it.
The caller claimed it was hovering over his house and coming towards him.
During the call, which was recorded and released by Hertfordshire Police, the operator assures him she will get it checked out.
But the man called back two minutes later to apologise to an exasperated operator.
Laughing nervously, he says: “I made a mistake. I thought I saw something really strange, but I didn’t. You won’t believe this, you won’t believe it. It’s the moon.”
Jason Baxter, assistant manager at Hertfordshire Police communications room, said: “While the caller here may not have been phoning out of malice, his call still tied up valuable police resources and time for something which was not an emergency.
“It also illustrates the kind of bogus call we might receive to 999, whether as a hoax or an inappropriate call.
“I would like to encourage people before they phone 999 to ask themselves is this really a police matter?
“Also, if you are thinking it would be funny to play a ‘trick’ this Halloween and make a hoax call, be very careful.
“You could find the ‘trick’ is on you when we prosecute you for making a hoax call.”