On Aug. 17, 2014 the Australian comet observer Terry Lovejoy discovered just another comet with his 20cm Schmidt-Cassegrain plus CCD camera, this time in Puppis. Comet C/2014 Q2 (Lovejoy) showed a significantly condensed 15" coma of magnitude 14.5-15.0 and a faint 1' tail in p.a. 225°. Follow-up observations determined a 25" coma of magnitude 14.8. The comet will reach perihelion at the end of January 2015, when it should be of magnitude 8.5 (CBET 3934 / MPEC 2014-R69). Beforehand it will approach earth, reaching a minimum distance of only 0.47 AU on Jan. 7, when it is expected to be of magnitude 7.5, showing a coma diameter short of 10'. For mid-European observers the comet will appear above the southern night horizon (constellation Columba) as an object of magnitude 8 around Christmas Eve. During the following four weeks it will not only reach maximum brightness but will rapidly cross through the constellations Lepus, Eridanus, Taurus, Stier, moving into Andromeda. It should be brighter than 15 mag until August 2015, thereby crossing the constellations Cassiopeia, Cepheus, Ursa Minor, Draco and Bootes.

The comet evolved much better than predicted and could be observed visually for more than a whole year, based on 413 observations by 13 members of the German Comet Section and 1550 international observations. Pre-perihelion the comet brightened very rapidly, finally enabling an unaided eye visibility for several weeks. Furthermore this positive trend was supported by an additional small brightening shortly before perihelion, with both factors yielding a maximum brightness of 4.0 mag around Jan. 14, 2015.

But an additional surprise was on hold. During the first three post-perihelion months the heliocentric magnitude did decrease extraordinary slowly, as did the activity of the comet. In consequence the comet faded very slowly for the terrestrial observers. Not until Apr. 25 did the heliocentric magnitude start to fade on average. In consequence the comet was still of magnitude 8.5 in mid-June, magnitude 11.0 in mid-September and 12.0 at the opening of November. The appropriate formulae are:

Alternatively, the post-perihelion brightness evolution can be represented equally well by the sole non-standard formula m = 2.8 mag + 5×log D + 1.68×r.

Heliocentric Magnitude

Total Brightness and Coma Diameter

While the apparent coma diameter was in the order of 1.5' at the beginning of the apparition, it significantly increased from mid-November 2014 onwards. Briefly after closest approach to Earth, around Jan. 12, 2015, it reached its maximum of 28'. Thereafter it shrunk, rapidly at first, then slower and slower. At the end of January 2015 it measured 20', in mid-February 15', in mid-April 8', in mid-June still 6' and at the opening of November short of 3'. In absolute dimensions the coma measured 150.000 km at the beginning of the apparition, starting to increase in early November 2014, reaching 575.000 km around Jan. 12, 2015. Thereafter it continued to increase in a decelerating manner until the end of May, when it measured 825.000 km - probably as a result of the very slow decrease of the high activity level during the three months following perihelion. Thereafter it shrunk, but measuring still 650.000 km in mid-October.

At the start of the apparition the degree of condensation was estimated to be DC 3-4. It increased slowly, reaching the maximum of DC 5-6 in mid-January 2015, which was hold until the end of February. Thereafter it decreased, reaching DC 3-4 in mid-June, DC 2-3 in mid-September and DC 2 at the start of November. The morphology showed a rather steep brightness gradient towards the comet's center which held a prominent stellar false nucleus. This reached a brightness of about 10.5 mag during January.

Visual Tail Length

The comet showed a quite dynamic and narrow gas tail which was observable visually between mid-December 2014 and beginning of August 2015, but was at no time conspicious. However, some knots in the tail were noticeable even for the visual observer. Visually the maximum tail length of 3° was reached in mid-January 2015. During the following weeks the tail was visible (but not conspicuous) in binoculars, with the length decreasing (mid-February: 2°, mid-March: 1°, mid-April: 0.4°). In absolute dimensions the visually discernible tail measured 6.5 mio. km in mid-January 2015 and peaked at 8 mio. km between the start of February and the start of March. In mid-April it measured still 4 mio. km. At the start of its visual visibility (around Dec. 20, 2014) the tail pointed northward, but turned rapidly to East until perihelion, only to turn slowly back thereafter, pointing towards Northwest in mid-July.

Andreas Kammerer

FGK observations