Comet Holmes in outburst captured remotely from RAS network (N.M.). Image: Ernesto Guido & Giovanni Sostero (AFAM, Remanzacco Observatory).

A comet in the direction of the constellation Perseus has unexpectedly brightened by a million times in the past 24 hours.

The source of this extraordinary event is comet 17P/Holmes, which is normally a magnitude 17 object -- just beyond the capability of the Hubble Space Telescope. The dwarf planets Pluto and Eris are magnitude 13.67 and 18.7 respectively.

But now the comet is visible to the naked eye, having brightened yesterday to magnitude 2.7, with current estimates stating its magnitude to be as high as 2.2 (1.6 times as bright). The actual figure is fairly subjective at this moment in time, though amateur astronomers say it compares well with the stars gamma persei and delta persei in Perseus.

Find Comet Holmes in the constellation Perseus looking northeast after sunset. AN Graphic.

Reports from the amateur astronomers (from as far afield as North America, Spain, Iran and Japan) suggest a golden-hued, fuzzy, star or planet-like appearance, with a bright 20 arcsecond interior surrounded by a greenish coma (suggesting the presence of cyanogen).

The reason for 17P/Holmes sudden brightness may be due to the comet's core breaking up, or possibly because of a collision with an unseen object. Details are sketchy at the moment and 17P/Holmes is small and 1.6 astronomical units away from Earth, making it difficult to discern any details, even with large telescopes.

Stargazers in Britain hoping to see 17P/Holmes may be thwarted by the weather. However, the comet is thought to have only begun brightening, allowing ample opportunity to make observations over the next few weeks. Early reports suggest that 17P/Holmes may have begun to grow a tail already.