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Armagh Observatory

Comet in Major Outburst Now Visible in Evening Sky

See also images taken on November 22nd

Comet Holmes
Image taken by Andy McCrea who says,
"To me the comet appears yellowish and it has gone from star-like to a
distinct disk in binos. But it is greenish in the 14" - the nucleus has been
very difficult to resolve - even with the webcam - it is surrounded with a bright
lobe to the left in my image and there appears to be distinct shells of gas - the
outer shell is strongly green in the images".

More images from Andy McCrea here.

A remarkable object suddenly became easily visible in the evening sky just a few days ago and continues to impress skywatchers around the world. At a quick glance, it looks as though a new, bright star has appeared; on closer examination, the star looks fuzzy. The true explanation is that a very faint comet, known as periodic comet Holmes, produced a massive outburst of material and became a million times brighter than it was just a day earlier.

Although astronomers today are able to predict a wide range of celestial events, from solar or lunar eclipses to meteor shower outbursts, the sky has not lost its capacity to take us by surprise. Such an astonishing event happened on 24th October, when Comet 17P/Holmes, which all summer had been a thousand times too faint even to be seen with binoculars, brightened within 24 hours to become comparable to some of the sky's brighter stars.

The comet is now moving away from the Sun, on the outward leg of an orbit with a period a little less than seven years. Currently some 150 million miles from Earth and 230 million miles from the Sun, it is visible all night and will remain fairly close to its present position, passing slowly through the constellation of Perseus, for several weeks.

Comet 17P/Holmes finding chart
An excellent finding chart can be obtained from
Reinder Bouma and Edwin van Dijk's web-site,
reproduced here with minor modifications.

Something has caused Comet Holmes to undergo an outburst, in which an extra amount of material is suddenly released from the comet's surface. The growing dust cloud, expanding away from the comet, reflects the Sun's light and allows us to see it from Earth. Indeed, a similar outburst caused the comet to brighten and led to its discovery by E. Holmes in England in November 1892.

Professor Mark Bailey, Director of the Armagh Observatory, said, "Astronomy is always full of surprises. These events make you think. Could the Star of Bethlehem have been a comet displaying a brightness outburst like this?" Terry Moseley, public relations officer for the Irish Astronomical Association wrote, "Comet Holmes continues to be one of the most amazing and fascinating comets ever observed."

It is difficult to predict what will happen next. Presumably the comet will dim over the next few weeks. But it could undergo another outburst, as happened in January 1893 two months after the discovery outburst. Professional and amateur astronomers will be following the comet closely in the coming days and weeks to find out.

Comets easily visible to the naked eye appear only a few times in a lifetime. Comet Holmes could be seen from the Observatory even through mist and in the light of the full moon. The comet is in the north-east in the evening, rising to nearly overhead later in the night. The constellation Perseus is roughly halfway between the recognizable W-shape of Cassiopeia, and the bright star Capella low in the north-east.

Two images, one taken on the 17th and the other on the 24th of October, are shown below (click on an image for full size version). Whereas the comet is invisible in the first, it is prominent next to the brighter stars in the latter. From the latter image a magnitude of 2.7 was derived for the comet, making it a little brighter than the star delta Persei to its right. The second image also shows a meteor (bottom left). These images were captured by the Armagh Observatory meteor cameras, which monitor the sky from Armagh every night, recording meteors when it is clear.

Comet 17P/Holes before outburstComet 17P/Holes after outburst

See also:
More images from Andy McCrea
Irish Astronomical Association - images and chart
Spaceweather.com - images
Nightskyhunter.com - images and charts
Seiichi Yoshida's Site - profile and pictures
Gary Kronk's Site
Size comparison with Jupiter from APOD

FOR FURTHER INFORMATION PLEASE CONTACT: David Asher or Miruna Popescu at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; djaat signarm.ac.uk; mdpat signarm.ac.uk

Last Revised: 2010 February 22nd