A 31-year-old UFO mystery was nothing more than a schoolboy science experiment, according to a man who has claimed responsibility for lights seen hovering in the Manawatu sky in the 1970s.

On a clear April evening in 1979 an orange light was spotted travelling in the night sky from Aokautere toward Hokowhitu.

Government documents released last week put this unexplained light down to a radar balloon "in the hands of people outside the meteorological service".

These official X-files show the light was spotted early in the evening on April 20, while other orange lights were seen in the region six days later.

Malcolm McCrea was then a 16-year-old fifth form pupil at Awatapu College.

He said that at school, a science teacher would build hot air balloons from tissue paper, cardboard, wire and cotton wool.

Using heat from a bunsen burner, the balloons would be released into the atmosphere.

About April or May 1979 those pupils decided the balloons would look better at night, so McCrea and his friends would release them into the atmosphere – powered by burning meths.

By stuffing different coloured tissue paper into them, the pupils could make a virtual kaleidoscope in the night sky, with the balloons ranging in size from a shoebox to a fridge.

The balloons would usually meander through the sky until an airstream caught them and made them rocket away – looking much like a silent alien aircraft speeding into the distance.

"We would often release several balloons at the same time, hence seeing something in a V-formation meant they were all caught in the same airstream," McCrea said.

Oddly enough, one of the April 1979 sightings was of three lights travelling in such a formation. There were also plenty of other reports in the media about unexplained lights in the night sky.

"We thought it was very funny."

McCrea, who now lives on the Kapiti Coast, said he released about eight or nine balloons himself – as did about 15 other people.

This likely explanation for Palmerston North's 1979 sightings did not surprise New Zealand sceptics spokeswoman Vicki Hyde.

While most sceptics would not rule out the possibility of other life forms existing somewhere, most possible UFO sightings could be explained.

"The bulk of [sightings] are from sincere people who have seen something they can't explain," she said.

"You don't have to be foolish to be fooled." Ms Hyde encourages people who see unexplained objects to keep an open mind about what they're looking at.

Another UFO sighting in Palmerston North happened in June 1972, when 17-year-old Jon Watson looked outside of his Crew Crescent flat and saw three silver objects flying 1000 feet overhead. "I got a fright at first," he told the Manawatu Standard at the time.

"We followed the three spaceships with our eyes for about a quarter of an hour. They were following each other and were quite close together."

Fourteen-year-old Freyberg High School pupil Gregory Key saw three "spinning silver objects" above Pahiatua on June 15 the same year.