It's been a while since we've had a big flare from the Sun. Active region 1515 was looking like it might do the trick -- over the past week this group of sunspots has been hissing and spitting, but the flares have been relative small. Astronomers rate flares by their X-ray energy: A, B, C, M, and X, where X is the highest. Some of the flares from AR1515 were C class and some M class - moderately strong.
Between July 5 and 6 it put out about a dozen of those smaller flares:
Then, late on July 6, it blew out the first X-class flare of the summer:
This sequence of images from the Solar Dynamics Observatory shows the flare over a bunch of different ultraviolet wavelengths, where flares are most obvious. You can see that it was pretty bright! Here's a video showing it erupting:
The video again shows the Sun at different wavelengths of UV light. The flickering is due to the software automatically setting the brightness level; when the flare gets bright it sets the image to be dimmer, so the Sun appears to flicker. The long dashed-line spikes are not real; those are due to the way the detector in SDO sees X-ray light, like the spikes you see in bright stars in some telescopic images.
Flares occur when the Sun's magnetic field gets tangled up. In a sense, the field short-circuits, releasing vasts of built-up energy, and we call that a flare. A big one can release 10% of the entire energy of the Sun! This can emit high-energy light and a huge blast of subatomic particles which cross the inner solar system and slam into us. While we're safe on the ground, this can damage satellites, cause blackouts, and of course trigger gorgeous aurorae -- the northern and southern lights.
This flare was still pretty small even for an X class; we had bigger ones over the past year (see the Related Posts for links to some of those). This particular group of sunspots is heading over the edge of the Sun now as our star rotates, so we probably won't be seeing it again; sunspots tend not to last that long. But there will be more. We're still approaching the peak of the sunspot cycle, probably late next year, so expect plenty more -- and more powerful -- flares to come.
Tip o' the welder's goggles to Camilla Corona SDO on Google+. Image credit: NASA/SDO
Related Posts: - HD Footage of last night's flare
- The Sun lets out a brief flare
- The Sun aims a storm right at Earth: expect aurorae tonight!
- GORGEOUS solar eruption!
- The birth of a sunspot cluster