This photo is a rough comparison in the sizes of Earth and Comet ISON.
Firstly, the tail is absolutely magnificent. Stunning, even.
To the meat of the matter.. Comet ISON’s solid nucleus, the mass that is being shed into space by the Sun’s heat, is no larger than a mile and a half wide. By comparison, Hale-Bopp was over 40 miles wide.
However, ISON’s coma (the vaporized gas gathered and lit up surrounding the comet nucleus) is over 100,000 km wide. Meaning, next to the Earth, it’s massive.