On July 13 the Australian Daniel W. Lynn discovered a 7.5m bright comet with his 10 x 50 binoculars in the constellation Hydra. The 4' wide, clearly condensed comet C/1999 N2 (Lynn) was only a few degrees above horizon when discovered, moving at 10'/h, indicating a small distance to Earth (IAUC 7222). Two days later the orbital elements confirmed this assumption, the comet just passed earth at 0.56 AE (IAUC 7224) at discovery.
31 observations made by 8 FG members of comet C/1999 N2 (Lynn) were received. Adding 190 international observations allows to present firm results. These figures seem to be small regarding the maximum brightness of 6.5 to 7.0m at mid-July, but are not so surprising by taking into account that comet Lynn got dimmer quite rapidly during the first weeks. The following diagram makes it clear, that the brightness evolution is only moderately described by the formula
The apparently "too faint" observations during the first weeks probably indicate, that comet Lynn just started to get active a short time prior to discovery. Poor conditions seem not to be a good explanation since the comet was well located for observers in the southern hemisphere at this time.
Increasing activity is also indicated by the evolution of the absolute coma diameter. It grew from 175.000 km at discovery to 375.000 km on August 20! Until the end of September the coma diameter was back to the size at discovery and even down to only 100.000 km at the beginning of November. The apparent size of the coma was stagnant at 7' at first, due to the combination of increasing geocentric distance and growing absolute coma diameter. It then decreased to 2.5' around mid-September and 1.5' at the beginning of November. The degree of condensation was high around mid-August (DC 5), but decreased rapidly to DC 3 at the end of August, slower thereafter to DC 1-2. Visual tail observations were rare but described lengths up to 0.3° (500.000 km).
Total Brightness and Coma diameter
Andreas Kammerer
