On images taken with the 30cm-astrograph of MARGO-observatory on Aug. 22, G. Borisov discovered a comet near the border of the constellations Orion/Taurus/Gemini. According to him comet C/2014 Q3 (Borisov) showed a 10" coma of total magnitude 17.0. Follow-up observations determined a significantly condensed 15" coma, a 25" tail in p.a. 225° and an elliptical orbit with a period of about 150 years. The comet will reach perihelion in mid-November, expected to reach magnitude 14.5 (CBET 3936 / MPEC 2014-R69). It will be brighter than 16 mag during the period mid-September to end of December, thereby moving through the constellations Auriga, Lynx, Camelopardalis, Ursa Minor and Draco, being a well-placed object for mid-European observers during the whole night.
The comet reached its maximum brightness of about 11.0 mag in early November 2014 as is shown by 16 observations by 3 members of the German Comet Section as well as 30 international reports. The brightness evolution can only be described moderately well with the formula
m = 8.5 mag + 5×log D + 10×log r At the opening of 2015 CCD-observations indicate a rapid fading: in mid-January a brightness of 15 mag was reported, at the end of February the reported magnitude was only 17 mag.Total Brightness and Coma Diameter
The apparent coma diameter increased constantly from 1' at the beginning of the apparition to its maximum of 5' at the start of December. Until early January 2015 it had decreased again to 3.5'. In absolute dimensions the coma increased steadily from 75.000 km at the beginning of the apparition to 375.000 km in early January 2015. Interestingly the coma got more diffuse during this period. The degree of condensation decreased from DC 4-5 to DC 0-1 in January 2015. No visual tail observations were reported.
Andreas Kammerer
