The flare, or coronal mass ejection (CME), was emitted on Monday at 8:56pm EST. It's been categorized as a Class X2.2 flare, the most severe type. It follows one Class M - medium-sized - flare the day before, and several low-grade Class C flares over the preceding week.
The coronal mass ejection associated with the flare is currently traveling about 900 Km/second and is expected to reach Earth's orbit tonight at about 10pm EST. It's the biggest flare yet in the current solar cycle.
NASA's Solar Dynamics Observatory captured the flare in the extreme ultraviolet wavelength of 193 Angstroms - although the SDO imager was for a moment overwhelmed by the bright flash.
It emanated from Active Region 1158, in the southern hemisphere; this has in the past trailed behind the north in activity but now leads in big flares.
A flare of this size could have noticeable effects on Earth when the cloud of charged particles reaches us. It's possible that radio transmissions and GPS systems could be knocked out, and power grids could be affected.
The increased radiation will represent a small health risk for astronauts on the International Space Station and even for air passengers and crew.
But, on the upside, as the charged particles hit the Earth's atmosphere, there's likely to be an impressive display of the Northern and Southern lights which could be visible much further from the poles than usual.