Did you notice anything different pertaining to the sun on December 4th — how about an enormous magnetic filament wrapped around the sun's south pole that erupted? NASA's STEREO (Solar TErrestrial RElations Observatory) is the third mission in NASA's Solar Terrestrial Probes program (STP), which are stationed on nearly opposite sides of the sun, photographed the blast from two points of view.

Astronomers have been monitoring eruptive prominences like this one for decades, but only now are they getting the 3D view provided by STEREO. "[In the past], we really had no idea in what plane the center of mass of the eruptive material was moving," says Joe Gurman of the Solar Physics Lab at NASA's Goddard Space Flight Center. But look again at the STEREO movie, particularly at the right-hand image. "The material is heading from high latitudes toward the solar equator," he notes. The dynamics of these massive events are becoming clear at last. More eruptions may be found in the STEREO gallery.

This two-year mission of STEREO, launched October 2006, will provide a unique and revolutionary view of the Sun-Earth System. The two nearly identical observatories, one ahead of Earth in its orbit, the other trailing behind, will trace the flow of energy and matter from the Sun to Earth. They will reveal the 3D structure of coronal mass ejections; violent eruptions of matter from the sun that can disrupt satellites and power grids, and help us understand why they happen. STEREO will become a key addition to the fleet of space weather detection satellites by providing more accurate alerts for the arrival time of Earth-directed solar ejections with its unique side-viewing perspective.

Other recent happenings include confirmation of a tsunami in February 2009 when sunspot 11012 unexpectedly erupted. The blast hurled a billion-ton cloud of gas (a coronal mass ejection, or CME) into space and sent a tsunami racing along the sun's surface. STEREO recorded the wave from two positions separated by 90 degrees, giving researchers an unprecedented view of the event.

"It was definitely a wave," says Spiros Patsourakos of George Mason University, lead author of a paper reporting the finding in Astrophysical Journal Letters. "Not a wave of water, but a giant wave of hot plasma and magnetism."