The image shows reflected light from dust grains and highlights the comet’s various tail structures. Similar images were obtained by amateur astronomers a few months ago when the comet was closer to the Sun and much brighter.
Most striking is the long trail, stretching over two degrees from the comet – equivalent to the apparent size of four full Moons on the sky as seen from Earth (see graphic below for scale) – or greater than 10 million kilometres at the comet's distance. By comparison, Rosetta is flying beside the comet nucleus as close as just 10 km.
The long trail is made up of larger grains left behind in the orbit of the comet, probably from several previous passages of the comet around the Sun. When the Earth passes through similar dust trails from other comets it gives rise to meteor showers. Unfortunately this won’t happen with 67P/C-G, as the orbit does not approach our planet.
The shorter dust tail just below the trail is a 'neck-line' structure, made from dust grains ejected by the comet during this current orbit.
Any anti-solar tail of the comet would be to the south but not so readily seen; in any case it would be very foreshortened in this geometry as the comet was at opposition, and at about 3 degrees phase angle, so the tail is mostly 'behind' the coma from our point of view.
See our previous blog post “Twin tails” for more about the comet’s dust trails.
Read more about the professional observing campaign in recent blog posts here and here, and keep up to date with latest images from the Professional-Amateur Collaborative Astronomy project community here and here.
Many thanks to Colin Snodgrass, Alan Fitzsimmons and John Davies for inputs to this blog post!