Comet Holmes (76P)

Comet Holmes visits the inner solar system every 6.88 years but usually goes unnoticed. This year (2007) it was predicted to be about magnitude 17 but after passing close to the Sun suddenly brightened by almost a million times to become visible to the naked eye. It was a lovely sight in Perseus, especially through binoculars. Here are some of the images that members of the Cauldron Club took.

Please click on the image for a larger view

Steve Loughran

Steve took these images on a Celestron NS8GPS using a William Optics ZS 66 SD as a guide scope. The image on the right is a straight colour image; the one on the left is the colour image with an added monochrome image that has been put through a Larson-Sekanina filter.

Trevor Nurse

The three images were taken on October 30th, November 6th and November 15th 2007 (from right to left). Trevor used a Canon 350D mounted at the prime focus of his SkyWatcher 100 ED Pro refractor.

Comet Holmes was discovered on November 6th 1892 by Edwin Holmes, a British amateur astronomer. Holmes was studyng the region around Andromeda when he spotted the comet which had brightened to between 4th and 5th magnitude. The outburst was similar to that seen this year (2007) which makes it more likely that the brightening is caused by something inherent to the comet rather than a collision. The chances of two collisions producing these outbursts are faily small.

Initial calculations gave it an orbital period of 6.9 years and it was observed again in 1899 and 1906 before being 'lost' again. It was recoverd by Elizabeth Roemer at the US Naval Observatory, Flagstaff in 1964 and has been observed regularly since then.

During this appearance it suddenly brightened by almost one million times, taking it from magnitude 17 to brighter than magnitude 3. At its brightest it looked like a new star in Perseus. It gave off a cloud of gas which looked like a disc through binoculars and as this grew it became apparent to the naked eye that it wasn't a star. As the cloud grew it first became larger than Jupiter, then exceeded the diameter of the Moon's orbit around the Earth.

The chances of a similar outburst on its next visit to the Sun are unknown but you can be sure it will be watched with eager anticipation as dedicated comet hunters try to be first to see the next big outburst. Might it be you?

If you want to add Comet Holmes to your planetarium or telescope control software, here are the orbital elements. I found it was already included in SkyMap Pro, the planetarium software I used most frequently, but if it's not in yours you should be able add it.

26th November 2007