By BBC News Online science editor Dr David Whitehouse

Two large and magnificent sunspot groups are travelling across the face of the Sun in an impressive display of solar activity.

Astronomers say that activity on the Sun's surface is increasing as it builds to a crescendo later this year, reaching the peak of its 11-year solar cycle.

For the first time, anyone with access to the internet can watch the Sun build to the solar maximum and look at its turbulent "surface" as it changes day by day. The last solar maximum, in 1989, occurred before the mass use of the internet.

A so-called Coronal Mass Ejection (CME) has just erupted following two intense solar flares. A CME is an ejection of super-hot gas into space. Sometimes, this stream of energetic sub-atomic particles can strike the Earth.

The magnetic fields contained within the stream interact with our planet's magnetosphere producing the spectacular Northern and Southern lights. But if the CME is particularly large event, it can also lead to interference with satellites, radio communications and, very occasionally, shut down power supplies.

The auroral light show caused by a CME last week was seen from space by the Ultra-Violet Imager on Nasa's Polar satellite.

"While the solar wind velocity was high last week, a strong gust triggered some interesting geomagnetic activity," said Dr Jim Spann of the Nasa's Marshall Space Flight Center. "I found it - a geomagnetic substorm over Asia - in the ultraviolet imaging data from the Polar satellite, which monitors aurorae from space. Without Polar, we might not have noticed."

Sun and climate

In a related development, an interdisciplinary study by astronomers and climatologists has found a striking correlation between structures in the Sun's "atmosphere" called coronal holes and the globally-averaged temperature of the Earth.

The study suggests that the Earth's atmospheric temperature may be strongly linked to solar magnetism changes over months or years.

The scientists compared the Earth's temperature with the size of coronal holes reported on the Sun during a two-decade period, starting in January 1979 and ending April 1998.

Results show a clear drop in terrestrial atmospheric temperature after the Sun's magnetic field activity is most intense.

"This is the first time anyone has combined these modern, reliable data sets to link solar activity and climate, and to cite several alternative mechanisms that might explain this link," Dr Eric Posmentier of Long Island University in New York explained.

Coronal holes are gaps in the Sun's outer atmosphere through which the stream of hot sub-atomic particles called the solar wind pours into space to engulf the entire Solar System. The solar wind has been long suspected as a possible indirect contributor to terrestrial climate change.

Dr Posmentier and colleagues think that the connection between the solar wind and climate may be more direct, suggesting that the charged particles hitting the Earth's atmosphere may affect the properties of terrestrial water clouds, particularly the percentage of clouds covering the Earth.