Spectacular aurora over NZ tonight

This extreme ultraviolet wavelength image provided by NASA shows a solar flare. It's heading toward Earth and could disrupt power grids, GPS and airplane flights. Photo / AP, NASA

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Those in the south of New Zealand should be able to see spectacular aurora lights tonight as the largest solar flare in five years reaches Earth.

Astronomer Dr Grant Christie from the Stardome Observatory said the particles from the solar flare should reach the earth around midday, New Zealand time.

"The actual flare occurred yesterday. It blew off quite a lot of material off the sun. That's called a coronal mass ejection. Typically they weigh about 10 billion tonnes of material. That goes out into space with a lot of force like a shotgun blast and satellites up there now monitoring the sun can monitor its trajectory in three dimensions.

"It's going to be a glancing blow to the earth."

Dr Christie said it is a class X5.4 flare, the strongest in more than five years.

An X1.3 flare occurred soon after the yesterday's X5.4. A solar flare on January 27 was a X1.7 flare.

"This one is quite a lot stronger than the one in January," he said.

"Any class X flare has got potential hazard to satellites, power grids, and aircraft navigation near the poles. So there are alerts out for that."

He said satellite operators will be rotating their satellites so that the hard back-end of the satellite is facing the sun to shield the electronics from the particles.

Dr Christie said the flare will only have an effect on flights over either of the poles.

"I understand airlines simply redirect those flights to avoid the hazard. The impact it has is not so much the radiation on passengers, it's the possibility of electronic disruptions to communications and navigations."

"Because the earth's magnetic field channels high energy particles onto the polar regions, which is why you see the aurora at the poles, there is much more intense electrical disruption at the polar regions than there are in our regions.

"Therefore the polar regions are where you expect to see more activity and therefore increased hazard."

Anywhere south of Auckland people should be able to see enhanced aurora over the next couple of nights.

"To actually get a good view anywhere in south Otago, Southland, Canterbury ... the further south you are the better. In Auckland you see the very top of the aurora, it's so far south a strong one will just peak over the horizon, it will look like a red glow in the south. As you get further south you will see colours like green appearing.

"It is a full moon as well so that will dim the impact."

Dr Christie said a big sun spot group, named AR1429, was the source of the solar flares.

"It's large, it's something like 10 times the size the earth would project ... nearly the size of Jupiter.

"You should be able to see it if you have the right sort of filter. I wouldn't encourage people to do it, but you can get safe solar viewers, from places like Stardome and the Royal Astronomical Society of New Zealand."

"It's not to say this will be the last flare, it's still possible there will be another eruption."