Comet 17P/Holmes, discovered in 1892, was visible only to astronomers with modern telescopes until the night of October 23, 2007 when it unexpectedly erupted.

The comet's coma, a cloud of gas and dust illuminated by the sun, has grown larger than the planet Jupiter. This "celestial surprise" can be seen over the next few weeks in the northern sky as a fuzzy spot of light about as bright as the stars in the Big Dipper.