Solar Terrestrial Relations Observatory B (STEREO-B) while observing the turbulent outer atmosphere (corona) of the Sun, gathered a novel view of our home planet and a celestial visitor in the inner solar system, Comet PanSTARRS. Image © NASA/GSFC/STEREO. Caption by Michael Carlowicz.
Comet PanSTARRS was visible to the naked eye from Earth’s northern hemisphere at the time, though STEREO might have had the better view.
The Heliospheric Imager (HI) on STEREO-B captured this image of PanSTARRS and Earth on March 13, 2013. At the time of the image, PanSTARRS was about 0.3 astronomical units (AU) from the Sun and about 1.1 AU from the Earth. Astronomical units are roughly the distance from the Sun to the Earth: 150 million kilometers or 93 million miles.
The HI instrument observes the area just off the limb of the Sun (left) in order to detect the faintly visible light of the solar wind and coronal mass ejections (CMEs) as they blow out into the solar system. STEREO-B was on the far side of the Sun from the Earth, at about a 150 to 160 degree angle from the Earth-Sun line. Puffs of solar wind and from a CME are visible in a video made from the same images in March.
In the image and video, PanSTARRS and its tail are the bright, wide mass in the center of the image. A coronal mass ejection is developing on the Sun’s limb (left), and Earth is to the right of the comet. The white dots in the background are stars. The vertical lines across the image are artifacts of the imager; the light of the comet, the Earth, and some planets and stars is too bright for an instrument trying to observe the faint light of the Sun’s atmosphere.