Bruce Murray Space Image Library

Comet ISON's perihelion from the STEREO spacecraft

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This animation includes images captured by STEREO Ahead on November 28 and 29. STEREO Ahead precedes Earth in its orbit. It happened to have a view on the comet almost directly perpendicular to the plane of the comet's orbit, the only spacecraft with such a perspective. As the comet approached the Sun, it was slightly in front of the Sun as seen from STEREO, so its tail was bright, its dust scattering light toward the spacecraft. As it departed, it was behind the Sun, at a significantly lower phase angle, so appeared dimmer. As time went on, the viewing geometry grew less favorable as the comet drew farther from the Sun, so it faded rapidly.