On Oct. 7, 1999 R.H. McNaught discovered a 15m comet in the constellation of Fornax on a frame taken by M. Hartley. Comet C/1999 T1 (McNaught-Hartley) showed a highly condensed 8" coma and a faint, 1' short tail in PA 320° (IAUC 7273). Orbit calculations showed that this comet passes perihelion in December 2000 at a maximum of about 6.5m, getting a binocular object for mid-European observers in the last month of that year. It became visible in the constellation of Libra in the morning sky, marching towards Draco, where most observers will lose it as an 11m object.
Until the end of October 2001 46 observations by 8 members of the German comet section were received. Taking into account 475 international observations, the following evolution can be derived: Until now the brightness evolution is extremely continuous and shows no significant differences between the pre- and post-perihelion period. It can be described very well by the formula:
resulting in a maximum brightness of 7.8m just at the beginning of the new millenium. The apparent coma diameter measured 0.5' (100.000 km) at the beginning of the appearance, slowly increasing to near 4' (275.000 km) at the perihelion, reaching its maximum of 7.5' (450.000 km) in mid-January. In the weeks following the coma diameter decreased, slowly at first, but more quickly at the beginning of April, to 3' (300.000 km) at that time. In mid-June it seems that the diameter decreased more quickly again to 1.7', followed by a period when it decreased slowly to 1.0' (170.000 km) in August/September. The coma was only moderately condensed during the first months (DC 2...3), condensing significantly in the weeks around perihelion, reaching a maximum of DC 6. Until mid-May it grew more diffuse again, reaching DC 2-3, where it since hovers. Visual tail sightings were reported during the period October 2000 to March 2001 with a maximum of 0.25° (1.4 Mill. km) in January. At the beginning the tail was oriented to the SW, at the end towards W.
Total Brightness and Coma diameter
Andreas Kammerer
