Solar flare The bright source of the flare can be seen close to the centre of the Sun
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The Sun has unleashed its strongest flare in four years, observers say.
The eruption is a so-called X-flare, the strongest type; such flares can affect communications on Earth.
Nasa's Solar Dynamics Observatory (SDO) spacecraft recorded an intense flash of extreme ultraviolet radiation emanating from a sunspot.
The British Geological Survey (BGS) has issued a geomagnetic storm warning, and says observers might be able to see aurorae from the northern UK.
The monster flare was recorded at 0156 GMT on 15 February and directed at the Earth. According to the US space agency, the source of this activity - sunspot 1158 - is growing rapidly.
Preliminary data from the Stereo-B and Soho spacecraft suggest that the explosion produced a fast but not particularly bright coronal mass ejection (CME) - a burst of charged particles released into space.
The unpredictable eruptions on the Sun can interfere with modern technology on Earth, such as electrical power grids, communications systems and satellites.
On Wednesday, the BGS released a rarely seen archive of geomagnetic records that provide an insight into "space weather" stretching back to the Victorian era.
BGS scientists say that studies of solar storms in the past could inform the prediction of future space weather and help mitigate threats to national infrastructure.
Displays of the Northern Lights (Aurora Borealis) have already been seen further south than usual in Northern Ireland and elsewhere in the UK. And further solar activity is expected over the next few days.
Researchers say the Sun has been awakening after a period of several years of low activity.
