Comet Holmes - A big surprise!

It wasn’t supposed to be a big show – but it is.

Visible in the night sky without binoculars or a telescope, comet 17P/Holmes has proven to be a bit of a puzzle to astronomers and an unexpected show for amateur sky watchers.

On October 24th, Comet 17P / Holmes surprised everyone by suddenly lighting up in the night sky. On the previous evening it was a tiny pin-prick of light, not visible by the naked eye, nor from amateur telescopes. The next day, Holmes had brightened almost a million times and had begun to grow in size.

How long have we known about comet Holmes?

Holmes is not a distant visitor like some other comets. It orbits the sun between the orbits of Mars and Jupiter, completing one journey in around 7 years. It was first spotted by Edwin Holmes, an Englishman in November 1892.

It’s now believed that comet Holmes was spotted due to a surge in brightness during 1892. Precise measurement of it’s brightness weren’t taken at the time, but professional observers noted that the comet was easily visible to the naked eye.

On Oct 24th, Holmes lit up. In 24 hours it changed from an object as dim and tiny as the former planet Pluto – which can just be seen in perfect conditions with a good quality amateur telescope – to a fuzzy blob and growing over the next few days to become one-half the size of the full moon. At this time, Holmes is easily spotted as a glowing spot in the sky. Obviously, your view will depend upon if you live in city or are near a source of bright lights.

What is happening on comet Holmes?

The common description of comets is that they’re ‘dirty snowballs’. If you imagine taking a handful of dirt, ice and bits of rock and pushing it together to form a ball, essentially that’s a fairly good description of a comet.

A comet therefore, is not made of one type of material. Various types of rocks and frozen liquids are part of it’s composition. As comets approach the inner solar system and the sun, they begin to warm up. The heating effect, caused by a wind of high-energy particles generated by the sun, whips past the comet. Some of the liquids on the surface come loose, and stream in the direction of the wind, producing the comet’s tail. As well, debris is left in the path of the comet, producing another fainter and curved tail.

The theory is that as a comet travels into the inner solar system and gets heated up, on each journey more frozen liquid material on it’s surface is melted away. Over time, what’s left, is a rocky shell which covers any remaining frozen liquids inside. The entire comet body is still heated by the sun, and jets of warmed liquid fly from cracks in the surface. Occasionally, enough of the liquid underneath the rock escapes to cause the surface to collapse – causing debris to cloud around the comet, and the remaining frozen liquid in that area to heat up and escape.

Even though Holmes is thought to be only 3.5 km in diameter, it’s spreading gasses are now thought to occupy a volume 300,000 km around the comet.

Read on to find out how you can find comet Holmes!