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On July 14, 2016 the PanSTARRS team discovered a comet of magnitude 21 in the constellation Hercules. Follow-up observations of comet C/2016 N6 (PanSTARRS) showed a strongly condensed 5x7" coma of total magnitude 20.0. The comet will pass perihelion at a solar distance of 2.7 AU in July 2018, expected to reach 14 mag (CBET 4309). It should be brighter than 16 mag between fall 2017 and spring 2019, with maximum brightness in spring 2018. During this period it will move through the constallations Bootes, Draco, Ursa Minor, Draco, Lynx (maximum brightness), Cancer, Hydra, Puppis, Canis Major and Lepus. Between mid-June and the start of September 2018 it will not be visible from mid-European sites.
Based on 174 observations from 29 observers the comet showed a very continuous brightness development, which can be well represented by the formula
m = 5.3 mag + 5×log D + 10.5×log r,
indicating a maximum brightness of 12.3 mag, which was reached at the beginning of April 2018 and at the opening of December 2018. The apparent coma diameter measured only 0.5' in 2017, but started to increase in February 2018, reaching 1.5' in May. In fall it reached its maximum of short of 2'. Thereafter it decreased, measuring short of 1' at the start of April 2019. The absolute coma diameter measured only 95.000 km in 2017, but started to increase in February 2018, reaching 225.000 km in May. In fall it peaked at 250.000 km. Thereafter it shrunk, measuring 125.000 km at the start of April 2019. The degree of condensation was constant at DC 3 in 2017, peaking at DC 5 in spring 2018, and was estimated at DC 4 in fall 2018 and DC 2-3 at the start of April 2019. Only CCD-observers detected a tail, with the length never exceeding 3' (1 Mill. km).Total Brightness and Coma Diameter
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On June 21, 2017 the ATLAS team discovered an asteroidal object of magnitude 18.0 in the constellation Cepheus, which revealed its cometary nature during follow-up observations. Comet C/2017 M4 (ATLAS) showed a moderately condensed 13" coma of total magnitude 17.5 and a short tail pointing SW. It will reach perihelion at a distance of 3.25 AU not prior to Jan. 18, 2019, expected to reach 14.0 mag in summer 2019 (CBET 4408 / MPEC 2017-N58). It will be brighter than 16.0 mag during the whole year of 2018 thereby moving from the border of the constellations Cygnus/Lyra through Hercules (maximum brightness) into Ophiuchus. From mid-European locations it will be observable until November 2018.Total Brightness and Coma Diameter
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In the course of the "Asteroid Terrestrial-impact Last Alert System" (ATLAS) an asteroidal object of magnitude 18.5 was discovered on Oct. 14, 2017 near the border of the constellations Cepheus/Draco. Follow-up observations showed the cometary nature of the object. Comet C/2017 T3 (ATLAS) showed a strongly condensed coma of diameter 15" and total magnitude 18.0 and a 60" tail in p.a. 155°. It will pass perihelion at a distance of 0.83 AU on July 19, 2018, expected to reach 9.0 mag (CBET 4449). However, it will then be positioned on the opposite side of the Sun and thus will not be observable well from any location on Earth. Mid-European observers can follow the comet until the end of March 2018 in the evening sky, then expected to be not brighter than 14.0 mag.
At only 15 mag in February 2018 this comet could be observed again by Southern hemisphere observers starting at the end of June, then at magnitude 9.5. Using 27 observations from 7 observers the brightness development can be represented well with the parameters m0=9.3 mag / n=4. This yields a maximum brightness of 9.2 mag on July 25, 2018. During those days the coma peaked at 4' (250.000 km). The degree of condensation increased from DC 4 at the end of June to DC 5-6 at perihelion, only to decrease thereafter, reaching DC 2-3 by the end of August. No tail sightings have been reported.
Total Brightness and Coma Diameter
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Comet C/2018 EF9 (Lemmon) was discovered by A.R. Gibbs as a 20 mag asteroidal object on images taken with the 1.5m-telescope on Mt. Lemmon on March 9, 2018. It passed perihelion on May 23 at a solar distance of 1.56 AU (CBET 4511). Surprisingly, it experienced a short-lived outburst between the opening of May and the start of June 2018, reaching about 13.0 mag around May 20. At this time it displayed an extremely diffuse coma of 3' diameter.
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On May 25, 2018 Henry Weiland discovered a comet on images taken in the course of the ATLAS project with the 0.5m-Schmidt-reflector on Mauna Loa Observatory in the eastern part of Sagittarius. The comet displayed a 12" coma of total magnitude 17 and a 12" westward-pointing tail. Follow-up observations of comet C/2018 K1 (Weiland) showed an extremely diffuse 1.0' coma of total magnitude 15.0 and confirmed the westward-pointing faint tail. The comet passed perihelion on Apr. 6, 2018 at a solar distance of 1.88 AU (CBET 4518). Only in May/June was the comet brighter than 16 mag, when it moved from Capricornus into the northern parts of Scorpius.
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In the course of the ATLAS project a comet was discovered on June 6, 2018 in Centaurus. Comet C/2018 L2 (ATLAS) showed a 20" coma of total magnitude 15.5 and a 27" tail in p.a. 92°. It will pass perihelion on Dec. 2, 2018 at the solar distance of 1.71 AU, when it is expected to reach magnitude 14.0 (CBET 4522). It should be brighter than 16 mag until April 2019. The comet will be visible from mid-European locations between October 2018 and April 2019 low above the evening horizon (SW to NW at altitudes of less than 20°) and in the morning sky during the first four months of 2019 above the eastern horizon (maximum altitude: 25°). During this interval it will move through Serpens, Ophiuchus, Hercules, Vulpecula, Cygnus and Lacerta into Andromeda.
According to 42 observations from 22 international observers the comet showed an outburst with a magnitude of more than 3.5 mag! Whereas the comet was of total brightness 13.8 mag on Sep. 5, 2018, the observers reported a magnitude of 10.1 on Oct. 1, 2018. After Oct. 6 (60 days prior to perihelion) the comet faded slowly, according to the formula
t > -60d: m = 9.0 mag + 5×log D + 0.015×(t-T),
but was still of magnitude 12.0 at the opening of March 2019 and of magnitude 13.0 at the end of this month. The coma diameter developed in a manner typical of an outburst. Whereas it measured 1.0' (100.000 km) at the start of September 2018, it swallowed to 4.0' (430.000 km) shortly after the outburst. Thereafter it decreased, measuring 2.0' (200.000 km) at the opening of February 2019 and 0.7' (85.000 km) at the end of March. Surprisingly, the outburst had no impact on the development of the degree of condensation. Until end of 2018 it was constant at DC 3-4. In 2019 the coma got more and more diffuse, reaching DC 2 at the opening of March. A tail was not observed.Total Brightness and Coma Diameter
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In mid-June 2018 comet 37P/Forbes (P=6.43a), which passed perihelion on May 4 (distance: 1.61 AU), will appear above the southeastern morning horizon. Until mid-August it will move from the eastern part of Aquarius to the head of Pisces. It should fade slightly from 12.5 mag to 13.0 mag.
In this apparition the comet showed a continuous rapid brightness development. Based on 79 observations from 16 observers the brightness development can be well represented by the formula
m = 6.0 mag + 5×log D + 29×log r
This yields a maximum brightness of 12.6 mag around May 25, 2018. At the beginning of the apparition the coma measured 1.1', increasing to the maximum of 1.5', which was constant between mid-May and mid-August. Thereafter it decreased, measuring 1.0' at the opening of October. This implies a continuous decline of the absolute coma diameter from 110.000 km to 55.000 km during the apparition. The coma was medium-condensed. The degree of condensation increased from DC 3 in April to DC 4 between the end of May and the beginning of July, thereafter decreasing, reaching DC 2 at the opening of October. No tail sightings have been reported.
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In mid-May 2018 comet 48P/Johnson (P=6.54a) should become brighter than 16 mag. Until mid-August, when it will pass perihelion (on Aug. 12 at the solar distance of 2.00 AU), it should brighten to 14.5 mag. During this interval it will move from the northeastern part of Capricornus to the border of the constellations Aquarius/Piscis Austrinus. During winter 2018/19 it will turn, then move northward towards the border of Cetus/Pisces.
In this apparition the comet showed a different brightness development pre- and post-perihelion. Based on 112 observations from 18 observers the derived time-dependant formulae are:
pre-perihelion: m = 12.3 mag + 5×log D + 0.019×|t-T|
post-perihelion: m = 12.3 mag + 5×log D
The formulae yield a maximum brightness of 12.3 mag around Aug. 20, 2018. The apparent coma diameter increased from 0.5' at the end of May to 1.5' at the end of July. This diameter was constant during the following six weeks. Starting in mid-September the coma diameter decreased, reaching 1.0' in mid-October and 0.5' at the end of December. The absolute coma diameter increased from 35.000 km at the end of May to 85.000 km at the end of June. Thereafter it began to decrease, reaching 60.000 km in mid-October and 45.000 km at the end of December. The coma slightly condensed during the first months (DC 3-4 at first, DC 5 in August). Thereafter it got more and more diffuse with the degree of condensation at DC 3-4 in mid-October and at DC 2-3 at the end of December. No visual observations of a tail have been published.
Total Brightness and Coma Diameter
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Starting in mid-July 2018 comet 66P/du Toit (P=14.90a), which passed perihelion at the solar distance of 1.29 AU on May 19, 2018, will appear above the southeastern morning horizon. At 12.0 mag the comet should fade to 13.0 mag until mid-August, with the comet positioned in the southern part of Cetus.
The comet showed a rapid brightness development, as can be derived by 75 observations from 10 observers. Based on these, the parameters m0=8.2 mag / n=10 and a maximum brightness of 10.7 mag around May 20, 2018 result. The coma diameter increased from 1.5' (75.000 km) at the beginning of the apparition to the maximum of 6.5' (240.000 km) at the start of June. Thereafter it began to decrease, reaching 2.5' (100.000 km) at the end of July and 0.5' (25.000 km) in mid-September. The coma was very diffuse. The degree of condensation remained between DC 1-2 to DC 2-3 (especially near perihelion). No tail was reported.
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On Jan. 27, 2018 comet 185P/Petriew (P=5.46a) will pass perihelion at the solar distance of 0.93 AU, expected to peak at magnitude 10.5. This comet possesses a high activity parameter (about n=12), which limits the time it can be observed visually. It should be brighter than 16.0 mag during the interval end of November 2017 and opening of April 2018. During this interval it will move – along the ecliptic – from the border of the constellations Sagittarius/Aquila to the northwestern corner of Orion. For mid-European observers it will be observable in the evening sky at an altitude of less than 25°.
Short of 30 observations could I use for a preliminary analysis. They show a rapid fade from 11.2 mag at perihelion to 14.0 mag at the beginning of April. These observations indicate brightness parameters of m0=11.0 mag / n=6. This means a much smaller activity parameter than the comet showed during previous apparitions. In parallel to the brightness development the coma diameter decreased from short of 2.5' (150.000 km) to only 0.8' (50.000 km) at the end of March. Throughout the apparition the coma was rather diffuse (DC 2). No tail had been recognized.
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Comet 240P/NEAT (P=7.62a), which will pass perihelion (at a distance of 2.13 AU) in May 2018, brightened more rapidly than expected between July 18 and Aug. 28, 2017, according to H. Sato. Whereas on July 18 the 15" coma was of total magnitude 17.3m (w-band), the comet was of magnitude 13.9 mag on Aug. 28, displaying a 1.3' coma. The tail length increased from 75" to 3' (CBET 4427). Observations during the following weeks showed a constant brightness, about 4 mag brighter than predicted. The comet peaked at 13.8 mag in mid-October 2017. Since than it fades slowly, reaching 15.0 mag at the start of January 2018. Between September and December 2017 the apparent coma diameter measured constantly short of 1.0', yielding a slight increase of the absolute coma diameter from 80.000 km to 100.000 km. So far the coma is rather diffuse (DC 2-3).
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On images taken on Jan. 16, 2018 with the 0.8m telescope on Calar Alto Erwin Schwab rediscovered comet P/2013 CU129 (PanSTARRS). Comet P/2018 A2 (PanSTARRS) was then a stellar object of magnitude 20.0. It will pass perihelion on June 24, 2018 at the solar distance of 0.80 AU (CBET 4474/75). Assuming the brightness parameters derived during the apparition in 2013 (m0=17.5 mag / n=2), the comet should peak at magnitude 14.0 mag in July. However, at that time it will be observable from the Southern hemisphere only. For mid-European observers it will disappear above the western horizon at the opening of June, then expected to be of magnitude 16.0. The comet received the permanent designation 364P/PanSTARRS.
The comet got considerably brighter than predicted, reaching a peak magnitude of 11.4 around July 10, 2018. Based on 41 observations by 7 observers the brightness parameters m0=15.4 mag / n=5 can be derived. The comet was situated quite close to Earth during this apparition, with the minimum distance of 0.24 AU reached on July 19. During many weeks it showed a highly condensed (DC 5-6), but remarkably small coma which is in line with the low absolute brightness. The coma diameter increased from 0.4' (short of 10.000 km) at the beginning of the apparition to the maximum of 1.7' (25.000 km) at the end of June, only to decrease again to 0.5' (10.000 km) until end of August. A tail was observed - visually and via CCD – between mid-June and mid-August, reaching a length of 10' (150.000 km). It was oriented eastward at first, then began to rotate towards South by end of June, pointing westward in mid-August.
Andreas Kammerer
