Copyright © 2007 by Emmanuël Jehin (Paranal Observatory, Chile)
E. Jehin took this picture on 2007 January 20. He was using a Canon 350D digital camera.
R. H. McNaught (Siding Spring Observatory, Australia) discovered this comet on CCD images obtained with the 0.5-m Uppsala Schmidt telescope on 2006 August 7.51. The images had been obtained as part of the Siding Spring Survey. He described the comet as magnitude 17.3, with a faint coma 20 arc seconds across in moonlight.
A very preliminary parabolic orbit was published on August 8 by B. G. Marsden. Using 19 positions spanning slightly more than one day, it indicated a perihelion date of 2007 June 17.71 and a perihelion distance of 1.555 AU. It also indicated the comet was over 3.5 AU from the sun, which meant a significant change in the perihelion date and distance was possible when more observations became available. Marsden revised his calculations on August 11. Using 39 positions spanning the period of August 7 to 11, he determined a perihelion date of 2007 January 11.74 and a perihelion distance of 0.170 AU, which indicated the comet could become a bright object in twilight. This orbit proved an excellent representation, as later calculations have shown a perihelion date of January 12.80 and a perihelion distance of 0.171 AU.
Confirmation came very quickly, C. Jacques and E. Pimentel (Belo Horizonte, Brazil) obtained CCD images using a 30-cm Schmidt-Cassegrain reflector on August 7.99. They gave the magnitude as 17.8 and noted the coma was 16 arc seconds across. Several other observers imaged the comet during the next few days. On the 10th, McNaught gave the total as 17.2, while François Kugel (A77) said his images indicated a nuclear magnitude of 17.4-18.7. On August 20 and 21, McNaught gave the magnitude as 16.9. On August 26, McNaught gave the CCD magnitude as 16.4.
The comet steadily brightened during September and more observers began following it. On September 5, McNaught gave the CCD magnitude as 15.9. On the 12th, McNaught gave the CCD magnitude as 15.4. On the 17th, D. Seargent (Cowra, New South Wales, Australia) gave the visual magnitude as 13.6. On the 18th, McNaught gave the CCD magnitude as 15.1. On the 20th, McNaught gave the CCD magnitude as 14.9. On the 22nd, M. Mattiazzo (Stockport Observatory, Blinman, South Australia) gave the visual magnitude as 13.1, while McNaught gave the CCD magnitude as 14.6. Mattiazzo said the coma was 2 arc minutes across and weakly condensed. On the 24th, Mattiazzo gave the visual magnitude as 13.3 and noted a coma 1.5 arc minutes across. On September 26, McNaught gave the CCD magnitude as 14.1.
The comet became a more difficult object to observe as October progressed because the comet's approach to the sun caused it to be observed at a steadily decreasing altitude as each day passed. On the 1st, McNaught gave the CCD magnitude as 14.2. On the 9th, Seargent gave the magnitude as 12.1. He said the coma was weakly condensed and 2 arc minutes across. On the 10th, the visual magnitude was given as 11.4 by Seargent and 12.5 by Mattiazzo. Seargent said the coma was 4 arc minutes across. Mattiazzo noted a coma 2.5 arc minutes across, while K. Yoshimoto (Hirao, Yamaguchi, Japan) gave the CCD magnitude as 13.8 and noted a coma 1.3 arc minutes across. On the 11th, Seargent observed with 25x100 binoculars and gave the magnitude as 11.1, while the coma was 6 arc minutes across. That same evening, M. Jäger and G. Rhemann (Austria) obtained 11 images of the comet using a Schmidt camera. After stacking the images, they noted a CCD magnitude of 12.0. They said the inner coma was 2-2.5 arc minutes across, while a faint outer coma was 6-7 arc minutes across. On the 12th, J. J. Gonzalez (Asturias, Spain) observed the comet at an altitude of 10° using his 20-cm reflector. He said the magnitude was 11.7, while the coma was 2 arc minutes across. On the 13th, Seargent observed using his 25-cm reflector and gave the magnitude as 11.3. He said the coma was moderately condensed and 3 arc minutes across. On the 14th, McNaught gave the CCD magnitude as 13.7. On the 19th, McNaught gave the CCD magnitude as 12.5. On October 24, McNaught gave the CCD magnitude as 12.1.
The comet was becoming very difficult in November, with most observations being made in some degree of twilight. On the 1st, G. W. Kronk (St. Jacob, Illinois, USA) gave the visual magnitude as 10.4. On the 9th, J. J. Gonzalez (Leon, Spain) saw the comet at an altitude of 5° and gave the magnitude as 9.8, while Kronk saw it at a higher altitude in twilight and estimated it as 9.6. Gonzalez also reported a coma 2 arc minutes across. On the 13th, Gonzalez gave the magnitude as 9.3. Among the last observations made before the comet was lost in twilight were those of Gonzalez on November 16.77 and Kronk on November 16.99. Gonzalez gave the magnitude as 9.1 and noted a coma 3 arc minutes across, while Kronk gave the magnitude as 9.3.
The comet was hopelessly lost in twilight during most of December, as searches by Kronk, Gonzalez, and B. H. Granslo (Fjellhamar, Norway) failed to reveal a trace through December 21. The comet was finally recovered in twilight on December 26.65, when P. Guzik (Krosno, Polonia) observed it using a 20-cm reflector. He estimated the magnitude as 4.5 and said the strongly condensed coma was 30 arc seconds across. On December 29, Granslo saw the comet at an altitude of 3.5° with his 10-cm refractor. He gave the magnitude as 3.9 and the coma diameter as 1.5 arc minutes. K. Kadota (Ageo, Japan) spotted the comet in bright twilight on December 30 and 31, using his 25-cm reflector and a CCD camera. For the first date, he gave the magnitude as 3.8 and the coma diameter as 1.7 arc mintues. For the second date, he gave the magnitude as 3.5 and the coma diameter as 2.0 arc minutes. Also on the second date, Kadota reported a tail extending 4 arc minutes toward PA 358°.
As 2007 began, the comet was still deep in twilight, but was brightening rapidly. David Moore (Dublin, Ireland) found the comet on January 1, just 3.0° above the horizon in strong twilight using 20x80 binoculars. He estimated the magnitude as 2.5-3.0. On the 2nd, Gonzalez found the comet using 25x100 binoculars when only 3° above the horizon. He gave the magnitude as 2.7. Gonzalez also said the coma was strongly condensed and 1.5 arc minutes across, while a dust tail extended 0.1° toward PA 0°. On the 5th, B. Leitner saw the comet in the morning sky and said it was easily visible in 8x30 binoculars. He estimated the magnitude as 1.5.
As the second week of January began, the number of amateur and professional astronomers spotting the comet skyrocketed, but the webmaster began receiving several dozen e-mails a day from people accidentally seeing the comet in the evening sky: from pilots flying at 30,000 feet to people walking their dogs. The last comet to get this type of attention was Hale-Bopp back in 1997. In the days that followed, comet McNaught brightened rapidly. It attained a magnitude of 0 on January 6, -1 on January 7, -2 on January 9, and -3 on January 11. The webmaster managed to take a total of nearly 250 images of the comet on January 8, 9, and 10, but was amazed to see the comet with the naked eye when it was so low to the horizon. On January 9, I last saw the comet's head when it was 0.8 degree above the horizon, and on January 10, I last saw the comet's head when it was 0.4 degree above the horizon. Also on the 10th, I noted the tail was visible for a few minutes more after I could no longer see the comet's head!
As the comet continued to approach the sun, it entered the field of view of satellites monitoring the area surrounding the sun. Comet McNaught entered the field of the Solar Terrestrial Relations Observatories (STEREO) satellites on January 11. Operators opened the door of the SECCHI/HI-1B instrument for the first time since the satellite was launched in October of 2006 and saw the comet. This image is listed further down the page with the other comet images. The comet entered the field of the Large Angle and Spectrometric Coronagraph (LASCO) camera aboard the Solar and Heliospheric Observatory (SOHO) on January 12. SOHO is orbiting the sun, not far from Earth, and has been imaging the sun 24 hours a day since 1996. It has photographed some of the brightest comets of the last 10 years, but when comet McNaught entered the field of view it was obvious that this was the brightest comet seem by SOHO. An image from SOHO is also displayed below.
The comet was at its brightest on January 13 and 14. Observers typically estimated the brightness as -5 to -6 and many were able to easily spot the comet in broad daylight just by blocking the sun with their hand.
Following its closest approach to the sun, the comet moved into the evening skies of the Southern Hemisphere and developed a spectacular tail that was being compared to comet West during March of 1976. Experienced visual observers were reporting that comet McNaught was between magnitude -2 to -3 on January 17, while the tail was 5 degrees long. The comet finally faded to magnitude 0 by January 22. As the comet climbed out of evening twilight, the tail became much more apparent. Terry Lovejoy (Queensland, Australia) estimated the tail length as 15 degrees on January 18, while Andrew Pearce (Western Australia) gave it as 20 degrees on January 19, and 24 degrees on January 21 and 22. Photographs began showing striae or luminous bands in the tail on January 17, while Lovejoy said the striae were visible to the naked eye on January 18. Jim Gifford (Bridgetown, Western Australia, Australia) estimated the naked-eye tail length as 35 degrees on January 23, 31 degrees on January 24, and 30 degrees on January 25. Gifford next saw the comet on January 29, with the moon in the sky. He estimated the naked-eye tail length as 13 degrees. On February 5, with no interference from moonlight, Gifford said the southern edge of the tail was 12 degrees long to the naked eye, while the northern edge was 6 degrees long.
The comet continued to slowly fade as March began, but the large coma caused a somewhat large variation in the magnitude estimates. On March 8, Alexandre Amorim (Florianopolis,Brazil) observed using 20x80 binoculars and gave the magnitude as 6.4. He said the comet was then 15 degrees above the horizon and displayed a coma 5' across. On the 10th, John Drummond (Gisborne, New Zealand) observed using an 8-cm refractor and gave the magnitude as 7.2. He added that the coma was 8.0' across, while the tail was about 12 degrees long. On March 11, Walter R. Robledo (Pilar, Argentina) observed using a 5-cm refractor. He gave the magnitude as 6.5 and the coma diameter as 3'. Gifford observed using 11x80 binoculars. He noted a magnitude of 7.1, a coma 8' across, and a tail about 1.4 degrees long. On March 15, Robledo observed with the refractor and gave the magnitude as 7.4. The coma was 2.5' across. On March 20, Stuart Rae (Hamilton, New Zealand) observed using a 25-cm reflector. He said gave the magnitude as 6.7 and the coma diameter as 9'.