Monster radiation burst from Sun
The Sun has unleashed its most powerful eruption of 2013 so far.
The solar flare - a sudden release of radiation - peaked at 1705 BST on Monday, and was associated with a huge burst of matter.
When these eruptions reach Earth, they can interfere with electronic systems in satellites and those on the ground.
Nasa said this solar explosion - known as a coronal mass ejection (CME) - was not directed at Earth, but it could pass several US spacecraft.
The event on Monday was classified as an "X-class" flare - the most intense type - with a designation of X2.8 (higher numbers denote a stronger flare). It surpassed an X1.7-class flare that occurred 14 hours earlier.
They are the first X-class events to occur this year.
When intense enough, a flare can disturb the Earth's atmosphere in the layer where GPS and communications signals travel.
This disrupts the radio signals for as long as the flare is ongoing - the radio blackout associated with this flare has since subsided.
CMEs can be even more disruptive because they can send billions of tonnes of solar particles into space. In those cases when very strong eruptions do reach Earth, the charged matter can blow out transformers in power grids.
The so-called Carrington Event of 1-2 September 1859 shorted telegraph wires, starting fires in North America and Europe, and caused bright aurorae (northern and southern lights) to be seen in Cuba and Hawaii.
The CME associated with this flare may pass the Stereo-B and Spitzer spacecraft. The operators of those science missions can choose to put their spacecraft into a "safe mode" to protect the electronics in onboard instruments from being tripped.
Increased numbers of flares are expected at the moment because the Sun's normal 11-year activity cycle is approaching a "high" of activity - known as a solar maximum.