The day the sun caught fire

This spectacular eruption of superheated gases, shooting a flame hundreds of thousands of miles long into space from the sun, was captured on film by an orbiting satellite.

The solar eruption, which is more than 240,000 miles long, burst from the surface of the sun yesterday as the satellite had its cameras trained on our nearest star.

The explosion is what astronomers call an eruptive prominence, a loop of magnetic fields that trap hot gas inside. As the trapped gas becomes unstable it erupts violently into space.

If eruptions like these are aimed at Earth, they can disturb the magnetosphere, the planet's magnetic field, with dramatic consequences.

Past eruptions have knocked out satellites, wrecked television reception and caused power surges and blackouts, but this one was fortunately not aimed at us.

Scientists say the sun is experiencing a solar max, a period of strong activity that happens about every 11 years and lasts for about three or four years.

The eruption is mostly burning hydrogen gas and solar particles which have been flung into space at around 100,000F, eight times the temperature at the core of the Earth, which is up to 13,000F - and hot enough to vapourise our planet should the Earth cross its path.

So much superheated hydrogen was involved in the eruption that although the gas is one of the lightest substances in the universe, it would have had a greater mass and weighed more than Mount Everest, our tallest peak.

The Soho satellite - short for Solar and Heliospheric Observatory - is a joint Nasa and European Space Agency project, orbiting the Sun a million miles from Earth. Its mission is to observe "space weather".

Todd Hoeksema, solar astronomer at Nasa, said: "This was quite a large eruption and they are pretty spectacular.

"The material goes out into space, and if it is heading towards Earth it will hit our atmosphere and disturb the magnetic field.

"It can damage satellites and sometimes means planes flying over the poles have to be re-routed, because it interferes with communications equipment."