Studying the Sun in 3-D: STEREO reaches new milestone at its sixth anniversary
On the evening of Oct. 25, 2006, the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft launched into space, destined for fairly simple orbits: both circle the sun like Earth does, STEREO-A traveling in a slightly smaller and therefore faster orbit, STEREO-B traveling in a larger and slower orbit. Those simple orbits, however, result in interesting geometry. As one spacecraft gained an increasing lead over Earth, the other trailed further and further behind. In February of 2011, each STEREO spacecraft was situated on opposite sides of the sun, and on Sept. 1, 2012, the two spacecraft and and the Solar Dynamics Observatory (at Earth) formed an equal-sided triangle, with each observatory providing overlapping views of the entire sun.