On March 19, 2010, the Sun's magnetic field erupted, launching a billion tons of plasma into space in an event called a coronal mass ejection. This particular CME headed right for Earth, but had no effect on us (except perhaps sparking some aurorae). It was captured from the side by NASA's STEREO spacecraft -- actually, two spacecraft, labeled A and B, which are far ahead and behind the Earth in its orbit around the Sun. A pretty nifty video of the STEREO A observations of this CME has just been released:
[Note: I suggest upping the resolution to 1080, and then making this full screen.]
The Sun is off to the right, and you can see the loops and glow from the plasma as it left the Sun at high speed -- about 350 km/sec (210 miles/sec). That's fast enough to reach us here on Earth in about 5 days. And yup, those are stars you're seeing in the background. At the distance to the CME, the scale of the video is about 48 million km (30 million miles) across.
On its way to Earth, this CME plowed past a satellite called ACE, designed to study subatomic particles ejected by the Sun (as well as from galactic and extragalactic sources, too). This means that CMEs like this one can be studied as they erupt, have their internal structures traced as they expand, and then studied as they impact us as well. As more are observed, we'll learn about how these giant eruptions are formed, and what impact they have on Earth.
The goal too is to understand them well enough to be able to predict their impact on us. A big CME can damage satellites and cause power grid outages on Earth, which can result in billions of dollars in economic loss. If they can be accurately predicted, it can potentially save us a lot of grief.
Video credit: Anthony Williams / NASA / Richard Harrison