C/2008 A1 (McNaught)

R.H. McNaught succeeded in the first comet discovery of the year 2008. On Jan. 10, 2008 he discovered a comet of magnitude 15.2 near the border of the constellations Puppis/Columba. Comet C/2008 A1 (McNaught) showed a medium-condensed 30" coma. It will pass perihelion in September 2008, probably reaching magnitude 7 (IAUC 8909 / MPEC 2008-C61). For mid-European observers it will appear on the evening sky at the end of October (at magnitude 8). Until the end of the year it will move through Ophiuchus and Hercules (at maximum altitudes of only 20°), thereby fading quickly to 11 mag.

The analysis is based upon 2 observations of members of the German Comet Section and 145 international observations (until the beginning of April 2009). These show a quite erratic brightness behaviour with several significant deviations from the mean evolution, which nevertheless can be described quite well by the formula

resulting in a maximum brightness of 6.7 mag in mid-September 2008.

Total Brightness and Coma Diameter

Between April and the disappearance into the twilight in July 2008 the apparent coma diameter was in the order of 4'. After the conjunction with the sun it measured 9' for several weeks. Beginning in October it decreased, measuring about 4' at the end of 2008. The absolute coma diameter decreased from 475.000 km to 350.000 km between April and July 2008. After the conjunction with the sun it measured 525.000 km, increasing to the maximum value of 650.000 km in November. Thereafter it began to shrink, reaching 450.000 km at the end of 2008. The coma was always moderately condensed. Until November 2008 the degree of condensation was rather constant at DC 4-5. Thereafter it decreased, measuring DC 2-3 at the end of 2008. Visual tail reports were very rare.

Andreas Kammerer