Comet ISON appeared in the higher-resolution HI-1 camera on NASA's STEREO-A spacecraft. Dark "clouds" coming from the right are more dense areas in the solar wind, causing ripples in comet Encke's tail. Using comet tails as tracers can provide valuable data about solar wind conditions near the sun.
Source: Karl Battams/NASA/STEREO/CIOC
Published: November 22, 2013