The image above comes from the SOHO “latest image” gallery, which shows the latest pictures from the Solar and Heliospheric Observatory (SOHO). An article on their website describes the passage of Comet C/2006 P1 (McNaught) through the satellite’s field of view.
The comet is passing close enough to the Sun to enter the field of view of the Large Angle and Spectrometric Coronagraph (LASCO), which normally monitors the faint glow of the Sun’s corona. Because the comet shines much more brightly than the tenuous gas flowing outward from the Sun, it appears as a bright, washed-out swath in the upper left of the image. What’s wonderful about the picture is that it’s data, collected in a somewhat clinical, unexciting fashion, that happens to show an unusual, transient phenomenon in our solar system.
Earthbound images of the comet can be found in a gallery of pictures taken from the ground.