Aurora Australis lights up Lake Rotoiti

Terry Urban had been following the right Facebook pages for years – looking for the perfect moment when he might spot an Aurora Australis.

The amateur Nelson photographer has taken photos of the natural phenomena before but on Saturday there was a particularly exciting alert.

The ‘‘KP level’’, which measures geomagnetic storm strength, was up to 7. This was rare for the Nelson region, he said.

The Southern Lights, or Aurora Australis, are caused by a geomagnetic storm - the result of a large hole in the Sun’s surface and a solar wind shock wave, which typically hits Earth’s magnetic field 24 to 36 hours after the event.

On Saturday night there was a particularly strong aurora. So at 7pm Urban packed up his camera and set out to Lake Rotoiti. It was almost completely dark when he arrived.

‘‘You can barely see it with the naked eye,’’ Urban said. ‘‘But the camera sensor can pick it up.’’

Then he set up his camera on a tripod and adjusted his settings - 30 second exposure and a f-stop of 2.8, to allow as much light to come into the lens as possible.

‘‘That red glow in the photo is actually the top of the aurora.

‘‘The further it goes down the earth the more yellow it gets. I wasn’t far south enough to pick up the yellows.’’

Urban said he first saw an aurora at Lake Tekapo when he was learning the craft. However, the photographs from Nelson Lakes were some of the better ones he has captured.

‘‘It’s incredible to see. You just stand there and almost forget to take the picture.’’

The Southern Lights were also spotted from Auckland, Canterbury and Otago on Saturday.