On August 4 at about 04:00 UT, the Sun let loose with another big flare, this one ranking as an M 9.5 or so on the standard flare classification, bigger than the one earlier this week. It also triggered a coronal mass ejection, which means we may get some effects here on Earth.
First, the way-cool video:
[Set the resolution to 720p or 1080p for the best view. Note: In the video title I said this happened on August 3. It did, in my time zone! It was August 4th in Universal Time, however. Sorry about any confusion.]
This is in the far ultraviolet, where energetic events like these show up well. The bright regions are actually sunspots, which are dark to our eye but are pretty glowy in the UV. At 03:57 UT the magnetic field lines in the spot reconnected, starting a cascade that released all the energy they contained. This caused the flare that's fairly obvious in the video. But you can also see material blasting away from the area, some falling back down. Finally, there are wispy tendrils of material arcing up that fade away.
What you don't really see here (but SpaceWeather has an animated GIF of it) is that this also sparked a coronal mass ejection (CME), a much larger explosion of energy that blasted roughly a billion tons of subatomic particles away from the Sun at the terrifying speed of nearly 2000 km/sec (1200 miles/sec). The energy involved in an event like this will crush your sense of scale to dust: it's the equivalent of the detonation of 500 million one-megaton nuclear bombs.
Of course, the 150 million kilometers between us and the Sun is a pretty big buffer. As the CME expands the energy spreads out a lot, and by the time it reaches here it's much weaker, though still significant. Now, don't panic: this happens a lot, and generally isn't too big a deal to us on the ground. This flare and CME were big but not nearly as big as the Sun can put out. However, it is expected this material will hit the Earth's geomagnetic field sometime today, probably around 14:00 UT (10:00 a.m. Eastern US time). If it does, it will probably spark aurorae at high to medium latitudes. I live in Boulder, so I'll be out tonight looking for them. You can check the NOAA Solar Weather page to see if you are inside the expected region to see the northern lights from this.
I doubt we'll see many satellite or cell phone problems from this, though it's possible. This sunspot (technically named Active Region 1261) still seems pretty agitated, so we may yet see more from it. It's rotating to the opposite side of the Sun, though, so it most likely won't do anything to us after this.
... but, as I've been pointing out, we're at the start of the solar cycle. It won't peak until 2013 or so, and it's around then we'll probably see the big fireworks. Again, we probably won't be affected here on Earth -- in 2003 we had some huge events, and we survived -- but brownouts and damage to satellites are always possible. I'll be keeping my eye on all this, and you'll hear about it as soon as I do.