The massive storm overwhelmed satellite sensors and looked set to produce brilliant displays of the northern lights.
But Nasa were watching the giant spot – which is bigger than the Earth – in case it fires more deadly levels of radiation hurtling in our direction.
The sunspot, labelled 930, unleased several massive blasts last week when it was near the edge of the Sun. Even though it was then pointed away from Earth, it registered as a loud roar on shortwave radio receivers and space station astronauts practised sheltering procedures.
Above is a photo I took at the weekend. Since then, the Sun has revolved and the spot, which had quietened down, has exploded back into life as it faces us. Experts said yesterday’s category S2 storm was not a danger to the shuttle cre, but could cause glitches and reboots on satellites.
UK solar expert Dr Lucie Green, of the Mullard Space Science Laboratory in Surrey, told me today: “These explosions are unpredictable and there is a real danger to astronauts if a big one goes off.
“X-ray and ultra-violet particles take just 20 to 30 minutes to get here from the Sun so Nasa would have to act quickly to move spacewalking astronauts.
“They have a limited amount of protection in their spacesuits but for a major flare they would need to find shelter within the space station.”
Two of the seven Discovery astronauts are due to make two more lengthy spacewalks this week to continue rewiring work and extending the space station.
If another, bigger flare is seen, Nasa expects to have enough time to order them inside to shelter behind water tanks before a dangerous wave of radiation hits them.
In August 1972, between the Apollo 16 and 17 missions, a powerful solar flare occurred that could have killed astronauts if they had been on their way to the moon or on the lunar surface. Life on Earth is protected from the effects of solar storms by our planet’s magnetic field.
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