17-11-2007 Comet Holmes surprises (Article 112)

Simon Kenny · Post by **Simon Kenny** » Wed Feb 04, 2009 11:34 am

Comet Holmes surprises (Article 112)

On October 24th last, amateur astronomers noticed something odd in the night sky. A new ‘star’ suddenly
appeared in the constellation of Perseus triggering an unprecedented flurry of excitement in the astronomy community as reports arrived from observers all over the world that this was actually not a star, but a once rather unassuming faint comet that had undergone an incredible one million-fold increase in brightness, in just 24 hours!
The comet in question is 17P / Holmes. Nobody knows what caused this massive outburst but history tells us this little oddball has a track record of misbehaviour. It did the same in November 1892 and was discovered by English amateur astronomer Edwin Holmes, hence its name.

As comets go, Holmes is one of the most visually impressive and strangest sights in living history. Usually these interstellar balls of dust and ice rock will begin to increase in brightness and may even develop a tail as the ‘melted’ ice and gas is strewn backwards as they approach the Sun, but the outburst from Holmes occurred suddenly and unexpectedly while on its way back out of the solar system. Last may it was closest to the Sun (perihelion). Each night it has increased in brightness and size and developed a beautiful green coma and blue ion tail (due to various emission gasses) but because of the awkward angle at which we are observing it (we are looking down the tail as opposed to side on) only long exposure photographs reveal the tail.

Holmes is still clearly visible with the naked eye and even better in binoculars. It appears as a large bright fuzzy ball nicely contrasted amongst the pinpoint stars around it. Our website has a map of where to look. Currently Holmes is about twice the distance away from us as Mars and massive in the extreme. The core is approximately only 3.4 km. wide but the coma is fast approaching the same diameter as the Sun, a whopping 1,391,980 km! Imaged from Limerick by David Lillis (SAC).