Analysis of Comet Apparitions

Home=Current Comets | The German Group | Tutorials | Archive: C/2018 W2 | Projects, publications | Images | Contact

C/2018 W2 (Africano)

On Nov. 27, 2018 B.M. Africano discovered a comet in Canes Venatici with the 1.5m telescope of Mt. Lemmon Observatory. Nearly at the same time H. Groeller recognized the comet on an image taken with the 0.68m-Catalina Sky Schmidt Telescope, however reported his finding after the discovery had already been published on the CBET pages. Comet C/2018 W2 (Africano) presented a 7" coma of total magnitude 18.5 and a southwestward pointing tail of serveral arcminutes length. The comet will pass perihelion in the solar distance of 1.45 AU on Sep. 6, 2019, expected to reach magnitude 10.5 (CBET 4580 / MPEC 2018-Y71). On Sep. 27, 2019 it will pass Earth in a distance of only 0.49 AU at an expected magnitude of 9.5. However, with a calculated coma diameter of about 5' it will not be an easily detectable object then. Between April 2019 and January 2020 it should be brighter than 16.0 mag. It should be observable from mid-European locations until end of October 2019. During this period it will move through the constellations Cepheus, Cassiopeia, Camelopardalis, Perseus, Andromeda, Pegasus (maximum brightness), Pisces, Aquarius and Piscis Austrinus.

This comet became the brightest comet in late summer and early fall 2019 and could be followed until Christmas 2019. According to 284 observations from 51 observers the brightness developed differently pre- and post-perihelion, best described by the formulae

The maximum brightness of 8.8 mag was reached during the time the comet passed Earth on Sep. 27, 2019.

Until end of July the apparent coma diameter increased from 0.4' to 1.5'. Due to the approach to Earth the apparent coma diameter increased during the following weeks much more rapidly, reaching the maximum of 8.5' at the time of closest approach. Thereafter it decreased in a similar rapid manner, reaching 4' in mid-October and 0.8' at Christmas. The absolute coma diameter increased steadily from 40.000 km to its maximum value of 210.000 km around perihelion date. Thereafter it decreased continuously, measuring 195.000 km at the beginning of September, 180.000 km at the opening of October, 160.000 km at the start of November and 95.000 km around Christmas.

The coma was moderately condensed during the whole apparition, with the degree of condensation remaining quite constant at DC 2-3 until perihelion. It increased to DC 4 until mid-October, remaining constant thereafter. Only a dozen tail sightings have been reported – all post-perihelion – with maximum lengths of 15' (2 Mio. km), pointing constantly towards Northeast.

Andreas Kammerer

FGK observations