Analysis of past comet apparitions

C/2008 Q3 (Garradd)


On Aug. 27, 2008 G.J. Garradd discovered a 18.5 mag comet with the 0.5m-Uppsala telescope in the constellation Phoenix. Comet C/2008 Q3 (Garradd) showed a considerably condensed 10" coma. It will pass perihelion in June 2009, when it could reach 12 mag (IAUC 8968 / MPEC 2008-U19). However, at this time it will be visible only from the Southern hemisphere. When it will appear above the mid-European morning horizon at the end of October of that year it is proposed to have faded already to 16 mag.

Actually the comet showed an extremely positive evolution during spring 2009, according to 155 international observations. At the end of April it was magnitude 9.5 - 5 mag brighter than predicted! The evolution can be represented by the formula

m = -0.4 mag + 5×log D + 30×log r

which indicate a maximum brightness of 7.0 mag around June 5, 2009.

The apparent coma diameter increased from 5' at the start of the visual apparition to a maximum of 16' at the beginning of June. Thereafter it decreased, measuring 4' in mid-August. The coma was medium-condensed with the DC-value slightly decreasing from DC 4 to DC 3.

Total Brightness and Coma Diameter

Andreas Kammerer


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