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Interesting fainter comets


On Oct. 31, 2010 A. Boattini discovered a 20.0 mag comet with the 1.5m-Mt.Lemmon-reflector near the border of the constellations Cetus/Aries. Comet C/2010 U3 (Boattini) showed a medium condensed 6-7" coma, elongated in p.a. 330°, harboring a 3-4" central condensation. Additional observations showed a 20" coma and a 25" tail in p.a. 330°. At discovery the comet stood in the record solar distance of 18.5 AU! It will not reach perihelion before spring 2019 at a distance of 8 AU. Nevertheless it could become as bright as 15 mag, then moving through far-northern regions (Camelopardalis, Ursa Major, Draco) (IAUC 9182 / 2010-V109). This implies an inherently very bright comet which showed a coma diameter of already 250.000 km at discovery!
The small number of observations published until the end of Apr. 2017 does not allow any definite statement concerning the brightness behavior of this comet. It should be observable with larger instruments as a 15.5-16.0 mag object in southern Camelopardalis during summer 2017, thereby exhibiting a well-condensed miniscule coma (of diameter 0.3-0.5').

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An asteroidal object of magnitude 20.5, discovered by T. Bressi on Spacewatch images taken on May 21, 2011 near the borders of the constellations Ophiuchus/Serpens showed cometary morphology on images taken in April 2012. Comet C/2011 KP36 (Spacewatch) displayed an 8" coma of total magnitude 20.0 and a very faint, 9" tail in p.a. 10°. The comet, intrinsically rather bright, will not pass its distant perihelion on its 235 years orbit prior to May 2016, then predicted to reach magnitude 14.5 (CBET 3109). It should be brighter than 15.5 mag between mid-2015 and the beginning of 2017. During this time it will move through the constellations Aquarius, Pisces and Cetus. The comet is expected to peak in September 2016.
Based upon 80 observations (until the start of February 2017) the comet shows a brightness evolution clearly below average. The derived brightness parameters are m0=7.0 mag / n=2, yielding a maximum brightness of 13.5 mag in mid-September 2016. In 2015 the coma diameter was estimated to be 0.5' (90.000 km) and in summer 2016 0.7' (125.000 km) was derived. However, the observations in fall 2016 hint towards a coma diameter of 1.2' (225.000 km). So far the coma is medium-condensed (constant DC 3).

Total Brightness and Coma Diameter

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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.
The small number of observations published until the end of April 2017 hints towards a brightness development below average, which could be represented by the parameters m0=8.5 mag/n=2. Thus the comet, which moves from the eastern towards the western part of Hercules, should show a constant brightness of about magnitude 14.5 during summer 2017. Earth will cross the orbital plane of the comet on July 22.

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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).

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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.
The small number of observations published until the end of April 2017 hints towards a brightness development below average, according to the parameters m0=10.0 mag/n=2. If these values should be confirmed by future observations the comet would peak at only magnitude 13.5. During summer 2017 it will move from Pisces/Pegasus into Aquarius, being best observable in the morning sky at first, and an object for the whole night at the end. Earth will cross the orbital plane of the comet on June 26.

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On June 22, 2016 the PanSTARRS project discovered a 19 mag comet in the constellation Draco. Additional observations of comet C/2016 M1 (PanSTARRS) showed a 10" coma of total magnitude 18.5 and a 12" tail in p.a. 180°. The comet will pass perihelion in August 2018, expected to peak at 9 mag (IAUC 4286 / MPEC 2016-N14). It will be brighter than 16.0 mag between April 2017 and the end of 2019. It will switch from the morning to the evening sky in December 2017 and should be observable for mid-European observers until end of June 2018 (then at 9 mag). During this period it will move through the constellations Draco, Hercules, Ophiuchus, Serpens, Aquila and Sagittarius.
The small number of CCD-observations published until the end of April 2017 indicate a brightness development according to the predictions. During summer 2017 it moves from Draco into the northern part of Hercules, expected to brighten from 15.5 mag to 14.5 mag. Earth will cross the orbital plane of the comet on June 23.

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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).
The small number of CCD-observations published until the end of April 2017 (covering the period August to December 2016) are inconsistent, but still compatible with an average brightness development of this comet. Thus it should brighten from 14.5 mag to 14.0 mag during summer 2017, moving from Andromeda into Cassiopeia, being best observable in the morning sky.

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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.

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On images taken on Aug. 26, 2016 the PanSTARRS team discovered a comet on the border of the constellations Capricornus/Aquarius, estimating the brightness to be about 21.5 mag, noticing a broad, 6" tail towards North. Detailed observations of comet C/2016 Q2 (PanSTARRS) showed a strongly condensed, 12" coma of total magnitude 19.0 and a very broad 12" tail in p.a. 338°. The comet (with an orbital period of about 440 years) will pass its perihelion at the large distance of 7.2 AU in May 2021, expected to reach about 15.5 mag. It should be brighter than 16 mag between spring 2020 and fall 2022, moving through the constellations Cygnus, Lyra, Draco/Hercules towards Ursa Major during this period (CBET 4311 / MPEC 2016-V116).

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On PanSTARRS images, taken on Sep. 7, 2016, a comet was discovered in the southern part of Eridanus. Comet C/2016 R2 (PanSTARRS) showed a very diffuse, miniscule coma of magnitude 18.0. It will pass perihelion (solar distance: 2.6 AU) at the start of May 2018 and should peak at about 12.0 mag around the turn of the years 2017/18 (CBET 4318 / MPEC 2016-U07). Between mid-2017 and mid-2019 it should be brighter than 16.0 mag. During this period it will move through the constellations Eridanus, Orion, Taurus, Auriga, Lynx, Ursa Major, Canes Venatici and Bootes. Thus it should be a well-placed object during the most-interesting months.
The small number of observations published until the end of April 2017 are rather inconsistent. The derived brightness parameters m0=4.0 mag/n=4 have to be confirmed eagerly by additional observations. During summer 2017 the comet is positioned near the border of the constellations Orion/Eridanus, reappearing for mid-European observers around Aug. 20 in the morning sky, expected to be of magnitude 13.0.

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On Nov. 6, 2016 the PanSTARRS team discovered comet C/2016 VZ18 (PanSTARRS) as an asteroidal object of magnitude 22 near the border of the constellations Eridanus/Cetus/Fornax (CBET 4351). At the end of December 2016 its cometary nature was detected and a maximum brightness of 16-17 mag predicted. However, at the end of February 2017 the comet was 3 mag brighter. It peaked at magnitude 13.5 in mid-March 2017, showing a very diffuse (DC 1) coma of diameter about 1.5'. Thereafter it faded rapidly.

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In the course of the LINEAR Sky Survey an asteroidal object of magnitude 19.5 was discovered on images taken on Jan. 26, 2017 near the border of the constellations Hydra/Corvus. Follow-up observations of comet C/2017 B3 (LINEAR) showed a significantly condensed 8" coma of total brightness 18.5 mag. This comet will pass perihelion at the beginning of 2019, expected to peak around magnitude 14-15 (CBET 4354). However, at this time it will be positioned in the far Southern Sky. It will not be observable from mid-European locations during the time interval when it is expected to be brighter than 16.0 mag.

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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.

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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.
The small number of published observations (covering the period from end of March until end of April) yield the parameters m0=11.0 mag/n=6 and a maximum brightness of 11.0 mag. The diameter of the medium-condensed (DC 3-4) coma was estimated to be about 2.5'.

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Comet 43P/Wolf-Harrington (P=6.13a) will appear in the morning sky in mid-August 2016, at an expected magnitude of about 11.0. Until the beginning of October it will move from Gemini into Sextans, thereby fading.
For the analysis of the apparition 2016/17 I could use 60 observations. These imply a brightness evolution according to the formula m = 7.5 mag + 5×log D + 17.5×log r, yielding a maximum brightness of 11.3 mag at perihelion. The coma diameter increased from 0.6' (65.000 km) at the start of the apparition to the maximum of 2.0' (190.000 km) at the end of September 2016. Thereafter it shrunk rapidly at first, reaching 0.9' (75.000 km) at the end of October. During the following weeks the decrease slowed with the coma measuring 0.7' (45.000 km) at the beginning of February 2017. During the whole apparition the coma was rather diffuse (degree of condensation constant at DC 3).

Total Brightness and Coma Diameter

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With medium-sized instruments observers could try to find comet 53P/Van Biesbroeck (P=12.59a) in spring 2016. It is situated near the border of the constellations Aquarius/Capricornus and should be an object of magnitude 13.
For a rough analysis 47 observations could be used. The brightness estimates can be rather well represented by the parameters m0=8.2 mag / n=4, yielding a maximum brightness of 13.0 mag in mid-July 2016. Until August the coma diameter increased from 0.5' (50.000 km) to the maximum of 1.2' (85.000 km), only to decrease thereafter, reaching 0.7' (75.000 km) at the end of October. During most of the apparition the coma was medium-condensed (DC 3), but became more diffuse during October.

Total Brightness and Coma Diameter

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The small number of observations of comet 65P/Gunn (P=7.64a), published until end of April 2017, indicate a development as predicted, according to the parameters m0=6.0 mag/n=4.5. Thus the comet should peak at magnitude 13.0 in June 2017, about 4 months prior to perihelion. It is positioned near the border of the constellations Scorpius/Libra and will disappear for mid-European observers at the end of July. Its medium-condensed coma shows a diameter of about 1'.

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Comet 71P/Clark (P=5.56a) develops as predicted, according to the brightness parameters m0=8.5 mag/n=6.5. Thus it will peak at magnitude 10.5 in June 2017. Due to its southern position in the southern part of Scorpius it is not observable from mid-European locations. At the opening of May 2017 the observers estimated the diameter of the significantly condensed (DC 5) coma to be in the order of 1'.

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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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Comet 144P/Kushida (P=7.57a) will appear in the morning sky at the beginning of September 2016. Until the start of December it will move from Cancer towards Virgo, thereby fading. According to the ICQ brightness parameters (m0=8.5 mag / n=8) it will be of magnitude 13. However, in 2008/09 the post-perihelion brightness parameters were derived as m0=6.0m/n=8. Thus the comet would be 2.0-2.5 mag brighter.
Only 35 observations could be used to analyse this apparition. The brightness evolution can be rather well described by the formula m = 7.2 mag + 5×log D + 17.5×log r, yielding a peak brightness of 11.5 mag at the start of September 2016. During the apparition the coma diameter shrunk continuously from 1.8' (160.000 km) to 0.7' (60.000 km). The coma was rather diffuse with the degree of condensation decreasing from DC 3 to DC 2. One international observer reported coma diameters of about 8' (700.000 km) and a maximum brightness of 9.0 mag. Comparing these values with previous apparitions, these estimates are rather unplausible. Applying the brightness parameters of the apparition 2008/09 to the current apparition yield a maximum brightness of 11.0 mag. The maximum coma diameter in 2008/09 measured 325.000 km.

Total Brightness and Coma Diameter

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One magnitude fainter than expected was comet 315P/LONEOS (P=11.23a) during winter 2016/17. It reached magnitude 14.0 at perihelion at the start of February 2017. The diameter of the medium-condensed (DC 4) coma reached 0.6'. The brightness parameters are in the order m0=9.0 mag/n=4.

Andreas Kammerer


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