A nebula with a 10-light-year head and a tail nearly 100 light years long
NASA's APOD description of the Cocoon Nebula points at a crowded starfield in Cygnus, the Swan, where the eye is drawn to the nebula itself — and then to a long trail of interstellar dust clouds to its left, which makes the whole complex look a bit like a comet.
The catalogue number is IC 5146. The bright central head spans about 10 light years, and the dark, dusty tail spans nearly 100 — so in this picture the "comet" is mostly tail, a dark streak of dust roughly ten times longer than the glowing part that gives the object its name.
AI-generated discussion · Different perspectives
The tail is dark in this visible-light image, and those filaments hide stars in the process of formation — the long streak is a stellar nursery as much as a resemblance.
What sells the comet comparison is pure geometry: a bright knot with a lane of material trailing off it, a shape the eye already knows from somewhere else.