With the assist of gravitational boosts from the moon, twin spacecraft in late January completed a series of maneuvers that will enable them to take three-dimensional images of the sun.
The pair of NASA craft, known together as STEREO (solar terrestrial relations observatory), was carried into space on a single rocket in October 2006 but then took different paths. On Dec. 15, 2006, one of the craft flew past the moon at a distance of 7,340 kilometers, using lunar gravity to move to a spot ahead of Earth in its orbit about the sun. The second craft received two lunar assists, the last on Jan. 21, when it flew within 8,818 km of the moon. Those kicks positioned the craft in an orbit trailing Earth.
The two observatories will slowly increase their separation from each other. In April, astronomers will begin using that separation, analogous to the distance between two eyes, to generate stereoscopic maps of activity on the sun. In tandem with an armada of other sun-tracking observatories on the ground and in space, STEREO will study the buildups and liftoffs of immense solar storms known as coronal mass ejections. When these billion-ton clouds of electrified gas rocket toward Earth, they can damage satellites and harm power grids on the planet.