17P-Holmes

Comet Holmes was discovered by the British in the late 19th century and was a most unremarkable, faint periodic appearance (Mag 17, which is really dim) until 2007 when it brightened by a factor of about half a million (mag 2.8, which is really bright), the greatest outburst ever recorded.

Position of comet 17P-Holmes during the 2007 outburst

It was, for a time, the largest body in the solar system, although its mass remained minuscule. It had the particularity of displaying a circular sphere of gas around is nucleus, with a short, faint blue tail. For this reason, it’s called the jellyfish comet.

Dramatic increase in size over a few days
Tracked exposure and apparent movement over one hour
True colour of comet Holmes was green

Processing shows internal structure and tail
Comet 17-P Holmes
Comet 17-P Holmes