The Canberra Airport "stationary silver object"

Canberra Airport, 1965. Pialligo, on the edge of the national capital. The airfield was shared. Civil traffic was run from the Department of Civil Aviation control tower, and the same ground housed RAAF Fairbairn.

The men in that tower watched the sky for a living. On the morning of Thursday 15 July 1965, that is exactly what they were doing.

Around 10:50 am, controller Tom Lindsey was scanning for incoming aircraft. He saw something that did not belong. The Australian described a "metallic silvery object, hovering in the sky to the north-east at an elevation of between 20 and 30 degrees." The Sydney Morning Herald, which spelled his name Lindsay, called it a "glowing white spot", like "the reflection of a light aircraft at a distance." The witnesses could not define its shape. No civil aircraft were in the area.

It did not leave. Controller A.F. Frodsham said it "hung in the sky for about 40 minutes." He weighed the idea of a reflection from an aircraft. He rejected it. The Herald counted six tower staff as witnesses, plus two pilots of a TAA Fokker Friendship just after take-off. On the RAAF side, base operations officer Flt Lt Weston was less certain. "It's hard to say whether it was stationary. At one time it seemed to be approaching us but I'm not sure."

Then it was gone. The press reported that it disappeared when an Air Force plane was sent after it.

They did not want an easy answer. "I've been in the job for two and a half years and I've never seen anything like it before," Lindsey said. "It wasn't Venus as has been suggested." The officer-in-charge, A.B. Lindeman, put it plainly. "I wish Mt Stromlo would tell us it was a planet. I don't like something in the back of my mind I can't understand." He was sure it was not Venus, he said, from the position.

Mt Stromlo Observatory was divided. T. Miller said there was "no astronomical explanation" for what had been described. "Heaven knows, it may have been an object from another planet." His colleague Dr Westerlund disagreed. A light in the north-east, he said, would almost certainly be Venus.

The RAAF moved fast. A telex from Headquarters Operations Command on 16 July read: "This headquarters has concluded that object was planet Venus. No further action will be taken." By 30 July the certainty had softened. A press release from the Minister for Air, Peter Howson, offered three possible causes. A short-lived contrail from a high-flying jet. Venus. Or a meteorological radar reflector balloon from Wagga, "clearly visible from long distances due to the reflecting sunlight."

Decades later, Keith Basterfield traced the files in the National Archives of Australia. He found no record that any RAAF aircraft had been sent, and no mention of radar. His software placed Venus due north-east at 23 degrees at 11:00 am, at magnitude minus 3.8. In 2011 Basterfield judged Venus the best match. By 2018 he left the case open, with the tower against the planet and the astronomers for it.

One more thread runs through the story. That same morning, Mariner 4 made its closest approach to Mars. Tidbinbilla had asked civil aviation to divert aircraft during the encounter. In a 2002 paper, Kerrie Dougherty of the Powerhouse Museum and John Sarkissian of CSIRO recalled the station's first ever call on a direct line from Canberra Airport, asking about interference from a UFO. Later, they wrote, the object was identified as an errant weather balloon. Whether that object was the one the controllers watched has never been settled.