By Dr David Whitehouse
BBC News Online science editor
One of the largest flares ever seen on the Sun is taking place right now.
Huge explosions rip away from the Sun
It comes from one of the biggest groups of sunspots seen for years. Several times in recent days superhot gas has erupted above them.
The events, called coronal mass ejections, have sent 10 billion tonnes of superhot material speeding towards Earth.
As well as communication blackouts, aurorae - polar lights - may be seen from mid-latitudes as the gas arrives.
Arrives in two days
According to reports, the flare is considerably more powerful than the two major flares that erupted on the Sun at the weekend.
It is the strongest flare since 2001 which itself was the most powerful since 1989.
A less powerful flare, also in 1989, caused disruption of power grids in Canada.
Observations from the Solar Heliospheric Observatory (Soho) satellite, monitoring the Sun from a gravitational balance point closer to the Sun than the Earth, indicate that a large mass of gas has been hurled towards the Earth.
It will probably slam into the Earth's magnetosphere in about two days.
Until scientists know the magnetic structure of the coronal mass ejection they will not be able to say if it will cause any disruption on Earth.
If the cloud has a southward directed magnetic field it will be severe, while if it has a northward component it will not affect us that much.
Observers say the eruption also caused a high energy proton shower which can cause damage to satellites and can be harmful for astronauts.