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A familiar comet, known since 1858, will pass perihelion for another time on Apr. 12, 2017. However, this year, comet 41P/Tuttle-Giacobini-Kresak (P=5.42a) will also be near the Earth (perigee at 0.14 AU occurs on Apr. 1). It is expected that this very diffuse comet will peak around magnitude 5-6, exhibiting a coma of more than 20' diameter. The apparition could get even more spectacular, if the comet would show one of its large outbursts (reaching up to 10 mag!) during the days around perigee. During the most interesting weeks the comet moves through the constellations Ursa Major, Draco, Hercules and Lyra, favoring Northern hemisphere observers.

The apparition 2017 proceeded unspectacular. The comet did not show an outburst and peaked at only magnitude 6.8 around Apr. 7. Based on 330 observations from 46 observers the whole brightness development (until end of April) can be described by the formula

m = 10.5 mag + 5×log D + 33×log r

The coma diameter started to increase rapidly at the end of January (1' = 20.000 km), reaching a maximum of 30' (190.000 km) during the final days of March. Thereafter it decreased, measuring 13' (110.000 km) at the end of April. During the whole apparition the coma was rather diffuse (DC 2-3 during the first two weeks, thereafter DC 3). With a telescope a brighter central condensation could be discerned, in which a false nucleus with a magnitude up to 13.0 could be seen temporarily. Visually no tail was reported.

Total Brightness and Coma Diameter

In the case the comet should continue to follow the brightness evolution listed above it will get fainter than 16.0 mag in mid-July. Until then it can be followed in the evening sky, moving from Hercules into Serpens.

Andreas Kammerer

FGK observations