STEREO'S ORBIT
STEREO is able to accomplish this feat because of the unique orbits of its two spacecraft. Each spacecraft is in its own orbit about the Sun (a heliocentric orbit) with orbital parameters that differ just slightly from those of Earth. It's these slight differences that make all the difference. The STEREO-Ahead spacecraft has an orbit that is a little bit closer to the Sun than Earth, and therefore orbits a little bit faster. STEREO-Behind, on the other hand, has an orbit just slightly outside Earth's, and is thus a little bit slower. The end result is that each spacecraft seems to slowly drift in opposite directions away from Earth by about 22 degrees per year, as illustrated below.
STEREO consists of two space-based observatories - one ahead of Earth in its orbit, the other trailing behind. With this new pair of viewpoints, scientists will be able to see the structure and evolution of solar storms as they blast from the Sun and move out through space.
This movie shows a spherical map of the Sun as it currently appears, formed from a combination of the latest STEREO Ahead and Behind beacon images, along with an SDO/AIA image in between. The movie starts with the view of the Sun as seen from Earth, with the 0 degree meridian line in the middle. The map then rotates through 360 degrees to show the part of the Sun not visible from Earth.
This movie shows a spherical map of the Sun as it currently appears, formed from a combination of the latest STEREO Ahead and Behind beacon images, along with an SDO/AIA image in between. The movie starts with the view of the Sun as seen from Earth, with the 0 degree meridian line in the middle. The map then rotates through 360 degrees to show the part of the Sun not visible from Earth.