An asteroidal object of magnitude 18.5 mag, which was discovered by the CATALINA-Project already on Oct. 23, 2013 in the constellation Eridanus, revealed its cometary nature during follow-up observations at the end of April 2014. Comet C/2013 UQ4 (CATALINA) showed a moderately condensed 25" coma that was surrounded by a large outer coma of up to 1.7' of total magnitude 14.0. In addition, a 15" tail could be observed in p.a. 330°. The comet rounds the Sun on an elliptical orbit with a period of about 470 years and will reach perihelion – close to Earth's orbit – on July 5. It will pass Earth on July 10 at a distance of only 0.315 AU (CBET 3882). Suggesting an average evolution it might reach 9 mag in the first half of July, showing a visually discernible coma of 7', according to my empiric formula. It may be brighter than 12.0 mag between June 10 and Aug. 10, thereby moving from Pisces through Andromeda, Cepheus, Draco into Bootes. Visible in the morning sky at first it will become an all-night and eventually an evening object during this period.
The comet was a difficult object visually. To estimate the size of the coma properly a dark sky was necessary. Accordingly large is the scatter of the estimates. For the analysis, 17 observations by 6 members of the German Comet Section and 95 international observations have been taken into account. The combination of the larger scatter and the rather small variance in the solar distance during the apparition lead to rather uncertain brightness parameters, which do not justify the use of different developments pre- and post-perihelion. The most plausible formula is:
m = 11.8 mag + 5×log D + 5×log rThus the comet showed a very low activity, peaking at magnitude 9.5 on July 10, the day of perigee.
Total Brightness and Coma Diameter
The apparent coma diameter measured 1.5' at the start of the apparition, increasing rapidly around June 20, reaching a maximum value of 6' on July 5. Thereafter it decreased slowly, reaching 1.5' again at the end of August. In absolute values the coma measured 50.000 km at the start of the apparition, increasing rapidly to 110.000 by mid-June, a value that remained nearly constant thereafter. During the most interesting weeks the degree of condensation was estimated to be around DC 2-3.
Andreas Kammerer
