Just another amateur discovery could be achieved by the Japanese Syogo Utsunomiya on Mar. 18, using 25x100 binoculars. The comet stood as a 9.5m bright object near the border of the constellations Pegasus/ Equuleus/Aquarius. Visually it showed a 1-1.5', only slightly condensed coma; on CCD pictures a 90' long tail pointing southwest could be recorded (IAUC 7854). The comet will come as close to the sun as 0.44 AU and reach a maximum brightness of 5.5m, according to first predictions. Unfortunately it will exhibit only small elongations during the most interesting period.
Until mid-June 11 observations by 4 FGK-observers were received. For the analysis 105 international observations ware added. This comet showed a steep brightness increase: during the first four weeks its brightness increased from 10m to 5m! Maximum brightness of 4.6m occured around Apr. 24. A few days before it had changed from the morning to the evening sky, thereby passing Mercury at a distance of only 3' on May 3. During those days it was an easy object in binoculars in spite of the rather bright twilight sky, showing a compact coma with a conspicious short tail. Thereafter, now getting slowly fainter, comet Utsunomiya became quickly invisible for mid-European observers. This comet showed a rather interesting evolution and has had the potential of being a rival to comet Ikeya-Zhang if only it would have attained more comfortable altitudes. The brightness evolution can be represented well with the formulae
Total Brightness and Coma diameter
Concerning the coma diameter only rough results can be derived due to the fact that the reported apparent coma diameter was severly influcened by the brightness of the sky background. According to the diagram the apparent coma diameter increased from about 2' (125.000 km) to a maximum of 3.5' (210.000 km). At the end of May it had already diminished to about 1' (70.000 km). The coma was moderately condensed (DC 4) at first, but condensed rapidly at the end of March / beginning of April, reaching DC 8 during the first week of April. It remained this much condensed until end of April, getting more diffuse thereafter, reaching DC 4 at the end of May.
Visual tail sightings were reported during whole April with a maximum of about 1.5-2° (5-8 Mill. km) around Apr. 15. It temporarly displayed a rather uncommon appearance: on the evening of Apr. 30, for example, the tail was wide opened (a great apex angle); at closer inspection it became clear, that the ion tail was situated at one, the (similar looking) dust tail at the other side of the fan.
Andreas Kammerer
