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Bright comets have been noted for some millennia, however it was not until 1705 that Edmond Halley described their source and destination. He realised that the comets seen in 1531, 1607 and 1682 were the same comet returning with a period of about 76 years. Halley's comet belonged to the Solar System and followed an elongated orbit about the Sun that took it from outside the orbit of Neptune to between the orbits of Venus and Mercury. Over 1,000 comets are known; about 160 of which have orbits within the inner Solar System and return to our view within periods of less than 20 years.
Comets are icy chunks of water and dust that originate in the outer Solar System. They used to b called dirty snowballs, but now are thought to be icy dirtballs! When they come near the Sun they vapourise, developing a bright tail.
Comets come from two main sources, the Kuiper Belt and the Oort Cloud:
Comets are thought to have been a source of water for the Earth, current discussion revolves around comets transporting amino-acids to Earth - amino-acids are the building-blocks of life.
| C/1995 01/Hale-Bopp | October 1995 |
| 9P/Tempel | May 2005 |
| C/2004 Q2/Macholz | January 2005 |
| 73P/Schwassmann-Wachmann | April 2006 |
| C/2006 M4 SWAN | October 2006 |
| 4P/Faye | November 2006 |
| P/2006 HR30 Siding Spring | February 2007 |
| 17P Holmes | November 2007 |
On July 23, 1995, an unusually bright comet outside of Jupiter's orbit (7.15 AU!) was discovered independently by Alan Hale, New Mexico and Thomas Bopp, Arizona. The new comet, designated C/1995 O1, is the farthest comet ever discovered by amateurs and appeared 1000 times brighter than Comet Halley did at the same distance. Orbital period - 4026 years; Diameter - 40km.
Ernst Wilhelm Liebrecht Tempel discovered this comet in 1867. Diameter ~4 miles, Orbital period 5.5 years.
In January 2005, NASA launched a Deep Impact mission to Tempel which will reach the comet on 4th July 2005. The craft will release an impactor which will crash into the comet, the main craft will relay pictures and data from the impact back to earth. Orbit period 5.5 years.
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9P Tempel in Virgo |
Comet C/2204 Q2 Macholz was discovered in August 2004 by Don Macholz, an amateur astronomer; he had previously discovered a further nine comets. Orbital period ~ 120,000 years.
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CometC/2004 Q2 Machholz 45mm lens Piggy-back on Meade LX200 Dorridge, UK
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| and three days later Machholz is past the Pleiades... | |
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CometC/2004 Q2 Machholz 215mm lens Piggy-back on Meade LX200 Dorridge, UK |
| and two further days later... | |
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CometC/2004 Q2 Machholz 136mm lens Piggy-back on Meade LX200 Dorridge, UK
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Note the green coma on the colour images of Machholz. The coma contains cyanogen (CN), a poisonous gas, and diatomic carbon (C2). Both of these substances glow green when illuminated by sunlight. Camera mounted at prime focus on LX200 GPS 10". |
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CometC/2004 Q2 Machholz
30secs f/10 Prime Focus on Meade LX200 GPS 10" f/10 Dorridge, UK
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Mosaic of Machholz's progress near
to Pleiades
Movement over |
Arnold Schwassmann and Arno Arthur Wachmann (Hamburg Observatory, Bergedorf, Germany) discovered this comet on photographs exposed for a minor planet survey on 1930 May 2.
The nucleus was split in 1995 August. The image below is of Component C - the largest fragment. There are three main fragments now visible: B, C and E.
A further 40 fragments, including very minor pieces, have been reported.
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Comet 73P/Schwassmann-Wachmann
2006 in Bootes |
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Comet 73P/Schwassmann-Wachmann
2006 in Serpens |
R D Matson (California) and M Mattiazzo (South Australia) independently reported this comet in July 2006. The comet was found on images obtained using the SWAN camera aboard the SOHO spacecraft. Comet SWAN is thought to have been in a long period elliptical orbit around the Sun which has recently been perturbed by Jupiter, or another large planet, and is now being sling-shot out of the Solar system .... and not to be seen from our region of the universe again!
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Comet C/2006 M4
SWAN in Corona Borealis Comet flared to brightness above mag 4.5 in late October 2006 as seen here. |
Comet Faye is a periodic comet discovered on 25 November 1843 by Hervé Faye at the Royal Observatory in Paris. Orbital period: 7.545 years.
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Comet 4.Faye in Cetus
Meade LX200GPS 10" f6.3 |
Comet P/2006 HR30 Siding Spring in Perseus; this animation shows
the movement of the comet over 9 minutes. The comet is much as an asteroid would
appear. In this animation two images taken 9 minutes apart have been used to
show the comet's movement.
Comet: Discovered April 20th 2006 by Robert McNaught and Gordon Garrard at
Siding Spring Observatory. Magnitude 11.7, Distance 198.4 million km.
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Comet P/2006 HR30 Siding Spring
Meade LX200GPS 10" f6.3 |
Comet 17P/Holmes outburst on 24th October 2007 by around 14 magnitudes, brightening by a million times and becoming visible to the naked eye. It was expected to be magnitude 17 and ended up brighter than Mag 3! The outburst grew to a diameter of about 4 million km and gradually dimmed over some weeks. A similar outburst was recorded in 1892 when it was discovered by Edwin Holmes. The comet's nucleus is about 3.6 km across; it orbits the sun every 7 years. The image below, taken on 11th November 2007, shows the comet past its brightest at a distance of 243 million km but still visible to the naked eye. My last view through binoculars was on 29th November 2007 when the comet was getting large, dim, and hard to find but had reached a really great diameter (much larger than the Sun)!
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Comet 17P Holmes in Perseus |
For more information on Comets, including those currently visible see the BAA Comet section website.
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