Earth hit by solar storm

The solar activity is expected to produce aurorae

Telecommunications may be disrupted briefly and the northerly and southerly night skies will shimmer red and green this weekend as intense storms rage on the Sun, scientists say.

The biggest sunspot cluster seen in at least 10 years has developed on the upper right quarter of the side of the Sun visible from Earth, according to satellite readings.

Nasa scientists said the most powerful flare erupted on Thursday, but it takes 24 to 36 hours for the effects to be felt on Earth.

It was rated a class X, the most potent category of sunspot, the other flares were less intense.

It is the biggest sunspot cluster for years

The eruptions triggered a powerful, but brief, blackout on Friday on some high-frequency radio channels and low-frequency navigational signals.

The flares are expected to persist for several days and experts are predicting that there is at least a 30% chance of disruptions continuing through until Sunday.

The solar activity is also expected to produce aurorae in the night sky over northern and southern latitudes.

Damage on the ground

The colourful, shimmering glow occurs when the energetic particles strike the Earth's upper atmosphere.

In addition to radio disruptions, the charged particles can bombard satellites and orbiting spacecraft and, in rare cases, damage industrial equipment on the ground, including power generators and pipelines.

The sunspot, which is a cooler, darker region on the Sun's surface, is caused by a concentration of temporarily distorted magnetic fields.

The solar flares are predicted to last for several days

It spawns tremendous eruptions, or flares, into the sun's atmosphere, hurling clouds of electrified gas toward Earth.

Monster sunspot

Geoff Elston, director of the solar section of the British Astronomical Association (BAA), has been studying the monster sunspot, Noaa 9393, for several days.

"It is definitely the largest we have seen for a long time, probably for many decades," he told BBC News Online. "It has overtaken the size of the most recent large one that occurred in March 1989."

Although very large by normal standards, Noaa 9393 is way short of the all-time record holder.

That title is held by a spot group that appeared in 1947. It was three times larger than Noaa 9393.