The Solar TErrestrial RElations Observatory (STEREO) is a two-year mission from the NASA Solar Terrestrial probes program. It is composed of two (nearly) identical spacecraft which will orbit ahead and behind the Earth, providing the first three-dimensional (3-D) observations of the Sun and the heliosphere. Among different suites of instruments, the focus here is on the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) and more precisely on the two coronagraphs and the heliospheric imagers. For a list of institutions involved in SECCHI, see here.

Artist's rendering of the two STEREO observatories looking at the Sun. Credit: NASA