Michael Jäger was able to take photos of comet C/1998 T1 (LINEAR) near the horizon shortly before closest approach to earth. From central Europe the comet looked like a tailless 9m object with a 2' coma on the morning of June 24. From a location in the southern hemisphere, where the observing conditions were much more favourable, visual observers reported an 8' coma on July 2, when the comet was nearest earth (0.485 AU). Based on 77 international observations the brightness evolution can be well handled by the following formula:
The formula yields a maximum brightness of 8.5m at the time of closest approach to earth. The apparent coma diameter was constant at 1.5' over several months, but grew from mid-May until the end of June, reaching 8'. Thereafter it decreased rapidly to 3' at the beginning of August and about 1' by Sep. 10. The absolute coma diameter grew from 140.000 km to 190.000 km at the beginning of the year and finally to 210.000 km at the end of June. It decreased since then and was around 170.000 km at the beginning of August. The degree of condensation was around DC 3 for a long period, increased to DC 4-5 during closest approach and then decreased rapidly to DC 2.
Total Brightness and Coma diameter
Andreas Kammerer
