Comet Holmes Explodes

Comet 17/P Holmes exploded during the College’s half-term, on Wednesday 24th October 2007. This type of event has never been seen before and may prove to be a once in a lifetime view.

Seen with binoculars, the apparent disc has the colour of polished brass. By eye, it appears as a fuzzy circular patch that forms a triangle with two stars in Perseus, just below the ‘W’ of Cassiopeia. Viewed through the College's 10" Barclay telescope, it is a spectacular shell expanding at some 2,000 kilometres per hour. The telescope also reveals some internal structure to the cloud (the Coma). 
  

Melting Snow 

Only a few of the hundreds of existing comets are visible by eye and even fewer are spectacular (such as Hyakatake in 1996, Hale–Bopp in 1997 and McNaught in 2007).

This comet, originally discovered in 1892 by E. Holmes in London, was the seventeenth Periodic (returning) comet to be found (the first being Halley’s comet). Comet Holmes orbits the Sun every six years but from 1906 was lost. It was picked up again in 1964, appearing as a very dim object only visible in the largest telescopes.

Then, in October 2007, Holmes suddenly brightened by a factor of one million. The cause of the explosion is unknown; it was possibly an impact or perhaps the comet had formed a crust which then shattered. In any event, around one percent of the comet's total mass is thought to have been lost.

The ‘bubble’ of debris is currently around one million kilometres in diameter, appearing as about half-the diameter of the Full Moon. It will expand over a week or so to the same size as the Moon but is dimming as it does so.

Being between Mars and Jupiter (only 400 million kilometres away), the comet, which is heading away from us, is also very close. 

The College Observatory will monitor its progress. It should remain visible throughout November 2007 and is conveniently high in the North East sky.