A Territorian could not believe his eyes when he saw a strange object beaming in the night sky.

John Ganter, 49, said he saw a bright green ball with two flaming tails flash across the sky.

''It looked like a comet, but with two tails,'' he said.

''It was quite a sight.

''I have never seen anything like it, just burning up in the sky.''

Mr Ganter was walking near Darwin's Nightcliff jetty about 8.30pm on Friday when he saw the unidentified flying object, which was visible for a couple of seconds.

''It passed left to right, approaching the vicinity of the full moon,'' he said.

''Then it stopped quite suddenly, it just went out.'' But Mr Ganter said he did not think he had seen a UFO.

''There is not a great deal of concrete evidence out there to support UFOs,'' he said. ''This didn't behave like an active object.''

Darwin astronomer Geoff Carr said the object was either a meteorite burning up or a decaying satellite that had re-entered the atmosphere.

''There are hundreds of disused satellites out there and every now and then one will re-enter the atmosphere,'' he said.

''Seeing a satellite is pretty rare -- it probably happens in the Territory once every five or six months.

''But a meteorite is more common.''

Mr Carr said burning meteorites usually lasted one to two seconds, and decaying satellites about four seconds.