ABOUT every third night Trevor Barry, a retired Broken Hill mine worker, turns his attention to the sky. What he has been seeing has delighted scientists around the world.

The amateur astronomer has been using his backyard telescope to record pictures of lightning crackling in a fierce electrical storm raging 1.4 billion kilometres away on the ringed planet Saturn.

First noticed in November by Cassini, an unmanned probe that has been circling Saturn for almost four years, the lightning bolts have been estimated to be 10,000 times more powerful than any seen in earthly storms.

To the untrained observer, what Mr Barry has recorded may look like a tiny white dot moving across the face of the planet as it rotates. But that dot is really a continuous series of lightning flashes so bright that they can be seen from Earth.

"I am imaging the lightning ... from Broken Hill, 1.4 billion kilometres away," Mr Barry said. "There must be thousands, probably hundreds of thousands [of lightning bolts] every second."

The entire storm, he added, "must be thousands of kilometres across".

He admitted he was awestruck by the display of nature's power being played out on another world. "I am stoked, fair dinkum."

Mr Barry is not the only one who is impressed.

He, and fellow amateur astronomers in the Philippines, the Netherlands and France, have been sending their images to Georg Fischer, a Cassini scientist at the University of Iowa.

There, Dr Fischer's team compare the amateur images with Cassini's observations. "Since Cassini's camera cannot track the storm every day, the amateur data are invaluable," Dr Fischer said.

In 2004 and 2006 the space probe also spotted storms on Saturn that lasted about a month. "But this storm is longer-lived by far," he said.

Although Cassini has photographed the tempest, most of its observations have involved recording the static-like noise generated by the lightning.

Dr Ulyana Dyudina, another Cassini scientist, said: "Whenever our cameras see the storm, the radio outbursts are there."

Mr Barry has been observing the storm since February. "From night to night it can be brighter or dimmer." But when the sky is clear and Saturn is in the right place in the sky, the storm is there. "It is the longest lived storm we know of on Saturn."

Scientists have no idea how long the storm, whipping through a part of Saturn's southern hemisphere now dubbed "storm alley", will last. However they hope it will provide clues to the workings of the planet's atmosphere.