The Sun does a lot of interesting things while it’s sitting out in space; not the least of which is to periodically fling billions of tons of charged particles out into space, with an average speed of 500 km/s.  These are Coronal Mass Ejections (CMEs), and they are quite a show.

USGov/NASA, TRACE

Often compared with solar flares, CMEs are (as the name suggests) massive ejections of matter from the Sun’s corona.  Not all CMEs are “pointing at” the Earth; many are discharged harmlessly into space.  It doesn’t have to be “spot-on”, either.  In traveling, the mass spreads out and accelerates (or decelerates) to about the speed of the solar “wind” (400-500 km/s).

When all this highly-charged mass hits the Earth’s magnetosphere, it compresses it on the “leading edge”, the side facing the Sun, and elongates the “following edge”, the side facing away from the Sun.  Of course, the particles falling back to Earth along the magnetic lines is what’s responsible for the Aurorae.

USGov/NASA, TRACE, Aaron Kasse

If unprepared, CMEs can cause a great deal of damage to satellites and power grids serving large communities.  The NASA-launched STEREO Mission, Solar TErrestrial RElations Observatory, allows for constant stereoscopic imaging and observation of the Sun.  This will give scientists enough warning (hopefully) when an extremely energetic CME is headed Earth’s direction.

For some very nice images of the Sun, take a look at these collected by TRACE.