A large sunspot has erupted, sending a coronal mass ejection hurtling towards Earth.
Coronagraph images from the Solar and Heliospheric Observatory (SOHO) and NASA's twin STEREO spacecraft show the plasma gas cloud as it was blasted out from sunspot 1123 in the sun's southern hemisphere during the early hours of Friday.
It'ss been classified as a C-4 solar flare, making it middling as solar flares go. But the filament of ejected material is headed more or less straight towards Earth at a little under 500 kilometers an hour.
NASA says it expects the cloud to deliver 'a glancing blow' to the Earth's magnetic field sometime tomorrow or the day after. "High latitude sky watchers should be alert for auroras on those dates," it says.
Only a few solar flares are powerful enough to produce coronal mass ejections. As well as massive quantities of matter - mostly protons and electrons - they release magnetic fields and electromagnetic radiation into space.
As a result, they can can disrupt radio transmissions and damage satellites and electrical lines. Mobile phone signals and other communications may be disrupted over the next couple of days, and there may be power outages.