The Sun is getting back into the swing of things: a big active region on its limb erupted yesterday (October 10), sending out a small storm of subatomic particles into space. We weren't in the line of fire, but over the next few days the rotation of the Sun will bring Active Region 11112 closer to the center of the Sun's disk, and if that region erupts it may send a storm our way.
Here's a recent image of the Sun from the Solar Dynamics Observatory:
This shows the Sun in ultraviolet (where activity can manifest itself) from around 23:00 UT (19:00 Eastern US time) on October 11. The active region is pretty obvious there to the lower left.
A magnetogram, which shows magnetic activity, makes the region obvious as well. A recent one (shown here on the left) from around the same time as the image above again shows the active region has a lot of magnetic activity going on.
The Sun's magnetic field lines can contain a huge amount of energy. As the gas in the Sun roils and swirls, the field lines get tangled together. If they connect, bang! They can explode, sending that energy out into space. The blast of particles can carry a magnetic field with it; if that connects to the Earth's magnetic field, it can dump some of that energy onto the Earth. We're safe here on the Earth's surface, but really violent solar eruptions can damage satellites and potentially cause harm to astronauts on the space station (who have to take refuge in a better protected part of the station until the storm ends, usually in a few hours).
What's funny is in visible light, not much can be seen from this region! Here's the Sun taken using a filter that only lets through blue-green light:
You can see the sunspot there in the lower left, but it sure looks innocent, doesn't it? Hmmm.
Now, to be clear: I don't think we have much to worry about here. If that sunspot decides to throw a hissy fit, it'll probably only create a pretty light show in the north latitudes; an aurora borealis. But as we saw in previous solar cycles, the Sun can be nasty sometimes. Hopefully we won't be seeing any of that! But we're on our way to the maximum of the solar cycle, sometime in 2013 or 2014. We'll see what happens then.