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On images taken on July 19, 2015 the PanSTARRS team discovered a comet in the constellation Capricornus, near the border to Sagittarius. According to the team comet C/2015 O1 (PanSTARRS) displayed a 2.5" tail towards East and a miniscule coma of magnitude 19.5. Additional observers reported a coma of diameter 15x17" and of total magnitude 18.5 and a 4" tail in p.a. 100°. The comet will pass its rather distant perihelion (distance: 3.7 AU) in February 2018, expected to reach magnitude 13.5 (CBET 4119 / MPEC 2015-Q71). It should be brighter than 16 mag between January 2017 and April 2019. During this period it will move from Aquila through Hercules, Bootes, Ursa Major into Lynx. Thus it will be comfortably placed in the morning/night sky for mid-European observers during the interesting weeks.
Based on 126 observations from 24 observers the brightness estimates can be best represented by the parameters m0=4.5 mag / n=4, which imply a maximum brightness of 12.8 mag at the opening of April 2018. Whereas the coma measured only 0.7' (110.000 km) in diameter in spring 2017, the reports indicate the maximum coma diameter of 1.4' (200.000 km) in spring 2018. In winter 2018/19 it still measured 1.2', indicating a diameter of 225.000 km. During the apparition the coma got more and more diffuse. The degree of condensation was DC 4-5 in spring 2017, DC 4 in spring 2018, but only DC 2 in winter 2018/19.
Total Brightness and Coma Diameter
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On PanSTARRS images taken on Nov. 2, 2015 an object was discovered which was slightly larger than the surrounding star images. Follow-up observations of comet C/2015 V1 (PanSTARRS) showed a 6" coma of magnitude 19.5, but no tail. The comet will reach perihelion at the end of 2017, then moving in Pisces and expected to be of magnitude 15.5 (CBET 4160 / MPEC 2015-V61).
Eighteen observations could I use for an approximate analysis. The brightness estimates can be quite well represented by the parameters m0=5.5 mag / n=4, yielding a maximum brightness of 14.5 mag in October 2017. The rather diffuse (DC 3) coma reached a diameter of 0.6' (100.000 km).
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On PanSTARRS images taken on Jan. 23, 2016 a team of observers discovered a 20 mag comet in the constellation Aries, which showed a miniscule coma and a short tail. It was shown, that this object was identical with the asteroidal object 2015 YY6, discovered by W. Yeung on Dec. 18, 2015 and with the object 2015 VL62, discovered on Nov. 2, 2015 at Mt. Lemmon observatory near the borders of the constellations Taurus/Auriga/Perseus. Additional observations of comet C/2015 VL62 (Lemmon-Yeung-PanSTARRS) showed a strongly condensed 8" coma of total magnitude 18.5m and a 15" tail in p.a. 80°. It will pass perihelion at the end of August 2017, then expected to be of magnitude 12-13 (CBET 4246/47). It should be brighter than 16.0 mag between end of 2016 and mid-2018, thereby moving from Aries into Scorpius. At maximum brightness it will move from Pegasus into Aquila, being observable for the whole night.
Until October 2017 I recognized 50 observations from 16 observers of this comet. The brightness estimates can be represented reasonably well by the parameters m0=10.0 mag / n=2, indicating a peak brightness of 13.5 mag around Aug. 20, 2017. Pre-perihelion the coma diameter increased from 0.4' (55.000 km) to 1.2' (90.000 km), only to decrease thereafter, reaching 0.4' (50.000 km) at the end of October. During the whole visual apparition the coma was rather diffuse, with the degree of condensation increasing pre-perihelion from DC 2 to DC 3-4, thereafter decreasing, reaching DC 2-3 at the end of October. Visually no tail was observed.
Total Brightness and Coma Diameter
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On images taken on July 15, 2016 by the MASTER telescope on Teneriffe an asteroidal object of magnitude 17.0 was discovered in the southwestern part of Cetus. By scrutinizinig the images a cometary morphology was dectected. Comet C/2016 N4 (MASTER) showed a strongly condensed 15" coma of total magnitude 16.5 and a tail up to 60" long in p.a. 190°. It will pass perihelion of its elliptical orbit with a period of about 1.000 years in September 2017, expected to peak at about 14 mag. During the most interesting months (mid 2017 to opening of 2018) it will move through the constellations Andromeda, Cassiopeia and Cepheus (CBET 4291 / MPEC 2016-P06).
Only 20 observations came to my knowledge. Thus only very approximate results can be presented. The brightness developed according to the parameters m0=7.0 mag / n=4. However the covered variance in solar distance was very small, thus the values are rather uncertain. The comet peaked at magnitude 14.5 in September 2017. At this time the coma diameter measured about 0.8'.
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On Feb. 23, 2017 the Brazilian observer J. Barros discovered a comet with the 45cm-reflector of SONEAR observatory in the constellation Telescopium, near the border of Corona Australis. Follow-up observations of comet C/2017 D2 (Barros)showed a significantly condensed 11" coma of total magnitude 17.5. The comet will pass perihelion on July 14, 2017 at a distance of 2.48 AU and should then peak at magnitude 15.0 (CBET 4366 / MPEC 2017-J52). It should be brighter than 16.0m between mid-May and mid-October 2017, thereby moving from the western part of Grus into Aquarius. It will not be observable meaningfully from mid-European locations.
The few published observations hint to a maximum brightness of only 16.5 mag in August 2017.
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On Mar. 1, 2017 Gennadii V. Borisov discovered a comet, using a 40cm robotic telescope, near the borders of the constellations Aquila/Sagittarius/Scutum. He estimated the total brightness of the 20" coma to be magnitude 17.0. CCD follow-up observations of comet C/2017 E1 (Borisov) showed a strongly condensed 50" coma of magnitude 14.0. S. Yoshida observed the coma visually on Mar. 3, estimating the brightness of the 1.4' coma to be magnitude 12.2. The comet will pass perihelion on Apr. 10, 2017 at the solar distance of 0.90 AU (CBET 4369 / MPEC 2017-J52). Alas, it is positioned on the opposite side of the Sun, and thus will be visible at only small elongations and not brighten more than one magnitude. Until end of August it moves through Aquarius, Pisces, Cetus into Taurus. From mid-European locations it will only be visible until end of March – at low altitudes in the morning sky. It will reappear in August, but with an expected brightness of less than 16 mag.
Only 20 observations of this comet came to my knowledge, indicating brightness parameters of about m0=10.5 mag / n=6 (neglecting the observations of one observer prone to estimating too bright and too large comae). The comet peaked at magnitude 10.5 at the opening of April 2017, showing a weakly condensed (DC 3) coma of diameter 2.5'.
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On May 29, 2017 Cristovao Jacques discovered a comet of magnitude 17.5 near the border of the constellations Grus/Tucana, using the 45cm telescope of the SONEAR observatory. Comet C/2017 K6 (Jacques) showed a significantly condensed 20" coma and a 55" tail at p.a. 245°. It will reach perihelion on Jan. 3, 2018 at a distance of 2.00 AU, expected to peak at magnitude 14.5 (CBET 4399 / MPEC 2017-N58). During this time, however, it will be positioned in Phoenix/Fornax, being unobservable from mid-European locations. These could succeed in observing the comet on its way out from the end of January onwards. It should be positioned in the constellation Eridanus when it fades below 16.0 mag.
The comet peaked at magnitude 14.0 at the turn of the years 2017/18. The medium-condensed (DC 3) coma reached a diameter of 1.5' (150.000 km). According to 30 observations the brightness development can be described fairly well by the parameters m0=6.5 mag / n=8.
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On images taken in the course of the Catalina Sky Survey on Sep. 30, 2017 a comet was discovered near the border of the constellations Lynx/Auriga. Comet C/2017 S6 (CATALINA) showed a strongly condensed 15" coma of total magnitude 18.0. It will pass perihelion on Feb. 26, 2018 in the solar distance of 1.54 AU, expected to reach maximum brightness of 15.0 mag already in December 2017 (CBET 4437 / MPEC 2017-V13). The comet is expected to be brighter than 16 mag between mid-November 2017 and the end of March 2018. During this period it will move through the constellations Camelopardalis, Cassiopeia, Andromeda and Pegasus. Mid-European observers can follow the comet until it will disappear above the western evening horizon at the end of January (expected to be of magnitude 15.5).
The development of this comet is documented by less than 10 observations. They hint towards a peak magnitude of 15.0 in December 2017. The medium-condensed (DC 4) coma reached 0.3'.
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Starting in mid-August 2017 comet 24P/Schaumasse (P=8.25a) should be detectable in larger instruments in the northeastern morning sky. During the following weeks it should brighten rapidly and should – using the parameters m0=7.5 mag / n=10 – peak at 10.5 mag around perihelion (distance: 1.21 AU on Nov. 16, 2017. In fall 2017 it will move from Gemini into Virgo, reaching greatest altitudes of about 40° in October.
In this apparition the comet remained one magnitude fainter than expected. The maximum brightness of 11.5 mag was reached in mid-November 2017. 85 observations could be used for the analysis, which indicate a brightness development according to the parameters m0=9.8 mag / n=4. However, it should not be concealed that two observers estimated the comet brighter (10.0 mag as peak brightness) and larger (up to 6') than the majority of the observers. Both observers, however, are prone to overestimations, for which reason their observations have been omitted. The coma diameter showed only minor variations and peaked short of 4' (240.000 km). The comet was rather diffuse (constant DC 2-3). No tail was visually discernible.
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Comet 65P/Gunn (P=7.64a) will pass perihelion again in October 2017. Due to its small eccentricity its development can be followed for two years in large amateur instruments. However, it will move through Scorpius and Sagittarius during the most interesting months, being a difficult object for mid-European observers.
I could use 35 observations. They indicate brightness parameters of about m0=7.5 mag / n=4, yielding a maximum brightness of 13.8 mag in June 2017. The maximum coma diameter of 0.8' (75.000 km) was reached in summer 2017, with the coma being rather diffuse (DC 2-3).
Total Brightness and Coma Diameter
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Comet 73P/Schwassmann-Wachmann (P=5.44a) peaked around the days of perihelion (mid-March 2017) at magnitude 11.5. According to the rather small number of observations the parameters m0=11.0 mag/n=6 have an inherent uncertainty. The diameter of the medium-condensed (DC 3) coma was in the order 1.5-2.0'.
During this apparition a fragment, designated BT, was discovered near the central condensation of the main component. Observations of this fragment have been published between the start of February and the start of March 2017. According to these it peaked at 11.0 mag during Feb. 15-25, thus surpassed the main component for a short time. Its medium-condensed (DC 2-3) coma reached a maximum diameter of 1.3'.
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The brightness of comet 93P/Lovas (P=9.20a) developed as predicted, peaking at 14.5 mag in February 2017. According to a rather small number of published observations the parameters m0=9.0 mag/n=7 can be derived. The diameter of the medium-condensed (DC 4) coma was in the order of 0.5-0.7'.
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A small number of published observations of comet 96P/Machholz (P=5.29a) support a pre-perihelion (perihelion occurred on Oct. 27 at solar distance 0.12 AU) brightness development consistent with the predicted parameters m0=15.0 mag / n=5. The comet brightened to 11.0 mag at the time it disappeared in the twilight (in mid-October 2017). Thus it can be expected that it peaked around 3 mag during the days of perihelion. Post-perihelion it will be situated very near the Sun for many weeks and therefore most probably no further observations will be possible.
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Comet 213P/Van Ness (P=6.12a) will pass perihelion for another time at the end of September 2017, possibly peaking at magnitude 11.5. However, during the preceeding perihelion passage the comet displayed an outburst. Thus we better should expect a fainter object. Alas, the comet will move through Sagittarius during the most interesting months.
In this apparition the comet showed an average development, according to 25 observations. The brightness development can be well represented by the parameters m0=10.5 mag / n=4, yielding a maximum brightness of 13.5 mag at the end of July 2017. The coma diameter measured 0.5' (25.000 km) at the start of the apparition as well as in mid-October. It reached a maximum of 0.7' (35.000 km) at the end of July. The coma was not much condensed with the degree of condensation constant at DC 3.
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In fall 2017 comet 217P/LINEAR (P=7.87a) should become visible in midsized instruments. The small number of observations published until July 2017 hint towards the parameters m0=10.5 mag / n=3. The comet peaked at magnitude 12.0 at perihelion (on July 17), showing a moderately condensed coma of diameter 2'. Mid-European observers will first have a chance in August, with the comet positioned in Orion (morning sky). Until the end of November it will move along the ecliptic to the borders of the constellations Cancer/Hydra/Canis Minor. It is expected to fade from 12.5 mag to 13.5 mag.
Based on 40 observations the comet showed a very high activity parameter in this apparition. Despite the small number of observations a different brightness development pre- and post-perihelion is evident. The comet brightened much more rapidly pre-perihelion than it faded post-perihelion. At magnitude 14.5 at the start of April it peaked at 12.2 mag at the end of July. At the end of October it had faded to 15.0 mag. The appropriate formulae are:
The coma diameter increased from 0.8' (50.000 km) at the beginning of the visual apparition to 1.6' (100.000 km) at the end of July, only to decrease thereafter, measuring 1.1' (70.000 km) at the end of October. The coma was medium-condensed with the degree of condensation at about DC 4 to DC 4-5. No tail was discerned visually.
Total Brightness and Coma DiameterAndreas Kammerer
