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Copyright © 2007 by D. Herald (Canberra, Australia)
D. Herald took this picture on 2007 April 9. The 7-minute exposure measures 5' across. The image has been reversed to better represent the comet's appearance.
Discovery
Gordon J. Garradd (Siding Spring Observatory, Australia) discovered this comet on exposures obtained using the 0.5-m Uppsala Schmidt telescope and a CCD camera on 2007 March 13.72. The magnitude was given as 14.6 and the coma was 35" across. The first independent confirmation came from A. Lepardo, V. Santini, and G. Sostero (Remanzacco, Italy) when they co-added 60 unfiltered 60-second exposures obtained on March 14.05 using a 45-cm reflector and CCD camera to reveal a diffuse coma almost 30" across, which was elongated toward PA 290°. They gave the magnitude as 15.2.
Historical Highlights
A preliminary parabolic orbit was published on March 14 by B. G. Marsden. Using 43 positions spanning slightly less than a day, it indicated a perihelion date of 2007 May 22.70 and a perihelion distance of 1.32 AU. Marsden revised the orbit on March 23. He took 106 positions spanning the period of March 13 to 23 and determined the perihelion date as May 23.10 and the perihelion distance as 1.29 AU. Marsden calculated an elliptical orbit on April 6. It gave the perihelion date as May 23.88, the perihelion distance as 1.29 AU, and the orbital period as 474 years.
Several additional observations were made on March 14. P. Birtwhistle (Great Shefford, Berkshire, UK) imaged the comet in poor seeing with this 40-cm reflector and described the comet as moderately condensed, 20" across, and elongated toward PA 300°. E. Guido (Italy) remotely observed the comet using a 25-cm reflector at Mayhill, New Mexico (USA) and noted a coma almost 30" across. D. Tibbets and G. Hug (Eskridge, Kansas, USA) imaged the comet using a 0.7-m reflector and said the coma was 15" wide and extended toward PA 280°. J. Young (Table Mountain Observatory, California, USA) photographed the comet using the 61-cm reflector and noted a round coma, 12" across, which exhibited a bright central condensation. He also noted a "hint of a poorly defined faint, broad tail structure" which spanned the region between PA 240° and PA 300° and was 40" long.
One of the earliest visual observations came on March 25, when V. Nevski (Vetebsk Amateur Astronomical Observatory, Belarus) saw the comet using a 30-cm reflector and gave the magnitude as 14.1. On March 27, A. Hale (New Mexico, USA) gave the magnitude as 13-13.5, as seen in his 41-cm reflector.
On April 6, B. King (Duluth, Minnesota, USA) observed using a 37-cm reflector. He noted the comet was large and diffuse, with a diameter of about 8'. After putting a SWAN band filter on the eyepiece, the coma was 10' across! He gave the magnitude as 10.7. Also on the 6th, Hale observed the comet using a 41-cm reflector. He estimated the magnitude as 11.0, the coma diameter as 4' and the degree of condensation as 3-4. On April 7, M. Meyer (Germany) saw the comet using a 15-cm refractor and gave the magnitude as 9.1. That same night, J. J. Gonzalez Suarez (northern Spain) observed using 25x100 binoculars and gave the magnitude as 9.3. He added that the coma was 7' across. On the 8th, G. Santa (Tiszaors, Hungary) observed using a reflector and gave the magnitude as 8.8. He noted that the coma was 15' across.
Additional Images
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