Until March 101 observations by 13 comet section members have been reported of comet 21P/Giacobini-Zinner. Adding 210 international observations the brightness showed a rather steep rise to perihelion and a significantly slower decrease thereafter:
indicating a maximum brightness of 8.5m in the second half of November. However, the graph of the heliocentric magnitude versa r shows no steady increase but instead that the increase of the he-liocentric magnitude slowed down during the approach of the comet to the sun.
Pre-perihelion heliocentric magnitude
Total Brightness and Coma diameter
The increase of the coma diameter from 2.5' at the start of September to a maximum of 5' in the second half of November primarily was the result of the diminishing distance comet-earth, because the absolute coma diameter did only increase from 170.000 km to 200.000 km. Thereafter, the coma dia-meter seems to have decreased to 2.5' (120.000 km). Parallel to this evolution the degree of conden-sation raised to a maximum of DC 5 in November, thereafter decreasing to DC 3-4 at year's end. During the second half of October numerous sightings of a 0.2° (0.6 Mill. km) long ion tail were reported. A dust tail could only be detected on a photograph by Michael Jäger, taken on Oct. 24.
Andreas Kammerer
