Giant sunspot may explode

The Sun is unusually spotty at the moment

By BBC News Online science editor Dr David Whitehouse

Scientists are currently observing the largest sunspot seen on the surface of our star for a decade.

Researchers think it could lead to a powerful flare some time in the next day or so. If this explosive event does occur, it will liberate in just a few seconds more energy than mankind has ever used.

The sunspot group, designated Noaa 9393, was first seen a month ago when it was not nearly so large.

The Sun's rotation took it from view but when it reappeared a few days ago astronomers were amazed that it had grown so big.

Over the past 24 hours it has become unstable displaying signs that its pent-up energy is about to be explosively released.

Monster spot

The sunspot is a monster according to Joe Elrod of the US National Solar Observatory at Sacramento, New Mexico: "This is the first big one we have seen during this solar cycle," he told BBC News Online.

Noaa 9393: Bigger than the Earth

Every 11 years or so the Sun goes through a peak of activity when there are more sunspots on its surface. Solar observers say that 2001 is the year of the current peak.

Noaa 9393 is so large that it is even visible to the unaided eye, though astronomers say that under no circumstances should anyone without proper protective equipment ever look towards our star as blindness can result.

Sunspots are regions of the Sun's surface that are marginally cooler than their surroundings. They only appear dark by contrast. If they were alone they would shine brighter than an arc lamp.

The 'big one'

They are caused when intense magnetic fields rise up from below the Sun's visible surface. They then become twisted and distorted by surface motions storing up vast amounts of magnetic energy.

Eventually, the magnetic energy becomes unstable and collapses, resulting in the explosive heating of vast amounts of gas. This is when solar flares are produced.

The most intense solar flares are called "white light" flares and it is this type of event that sunspot group Noaa 9393 is expected to produce.

"We saw two small flares yesterday, and they may be the precursors to the big one," Joe Elrod said.

Scientists say that the Sun is currently going through a particularly active phase with many groups of sunspots on its surface.