An apparently asteroidal object, discovered by the LINEAR-team on Nov. 13, 2006 near the border of the constellations Andromeda/Lacerta showed cometary activity at closer inspection on Dec. 1 and 2. Comet C/2006 VZ13 (LINEAR) presented an 8" coma of magnitude 18.5 despite bright moonlight. The comet will pass perihelion - near the earth's orbit - in August 2007, perhaps reaching 10 mag (IAUC 8781). Between the start of June and the beginning of October it is expected to be brighter than 13 mag. Due to its movement through the constellations Andromeda, Cepheus, Draco, Bootes towards Virgo it will disappear - already fading - in the evening twilight around Aug. 10 for mid-European observers.
Actually the comet brightened much more, becoming even visible in binoculars. According to 35 observations by 8 observers of the German Comet Section and 180 international observations the brightness evolved very steadily, according to the formula
m = 8.2m + 5×log D + 11.8×log r
reaching a maximum of 7.5 mag around July 15 (the date of perigee).
At the beginning of the apparition the coma diameter measured about 1' (125.000 km). During the first weeks it increased slowly, reaching 4' (200.000 km) on June 20. Thereafter the increase accelerated with increasing pace, reaching a maximum of 14' (375.000 km) on July 15. Immediately thereafter it decreased at a similar pace, reaching 5' (225.000 km) around Aug. 10 (probably intensified by the degenerating observing circumstances). Throughout the apparition the coma was rather diffuse (DC 3), with the degree of condensation reaching DC 4 during the four weeks around perigee. Within the diffuse coma was a brighter inner region discernible, which however did not show any false nucleus brighter than 14 mag. In July a few visual tail sightings were reported with maximum lengths of about 0.25° (400.000 km).
Total Brightness and Coma Diameter
Andreas Kammerer
FGK observations