Summary:

•    How and why does the Sun vary?
•    How do the planets and Earth respond to that variation?
•    What are the impacts for humanity?

For decades, the search for answers to these fundamental questions has preoccupied solar and space physicists and has driven the plans for all Sun Earth Connections (SEC) missions. Although significant inroads were made with single-spacecraft missions, a radical new approach is called for to advance our understanding of our nearest star and its wide-ranging effects on interplanetary space and, more importantly, on our home planet. The STEREO mission is designed to view the three-dimensional and temporally varying heliosphere by means of an unprecedented combination of imaging and in situ experiments mounted on duplicate spacecraft flanking the Earth in its orbit. The advantages of stereoscopic vision are imprinted on our very DNA, yet we are only now becoming sufficiently adept to use the same principles to construct a truly global picture of the active Sun and its influences.

SECCHI is named after one of the first astrophysicists ( Angelo Pietro Secchi, 1818-1878). Angelo Secchi was a Jesuit priest. He was one of the first astrophysicists to use the new medium of photography to record solar eclipses. He photographed the 1860 eclipse, during which a CME is now thought to have occurred. 1860 CME figure.