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Analysis of Comet Apparitions


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Current Fainter Comets of Interest


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!
At the end of April 2018 the number of published observations is still too small for a definite analysis. However, for the first time it is possible to derive preliminary values. The brightness development can be described by the parameters m0=6.5 mag / n=2. This yields a constant brightness of the comet of 16.0 mag between May and August 2018 and a maximum brightness of 15.5 mag at the turn of the years 2018/19. So far the comet exhibits a well-condensed miniscule coma (of diameter 0.4-0.5').

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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.
The analysis can be based on 95 observations, which in the meantime cover a sufficient variance in the solar distance, to derive meaningful values. The brightness development can be described rather well with the parameters m0=5.4 mag / n=3, yielding a maximum brightness of 13.6 mag in September 2016. The estimated coma diameter peaked at 1.2' (240.000 km) at the same time in 2015 and 2017 it measured only 0.5' (90.000 km / 125.000 km). Throughout the apparition the coma was medium-condensed (constant at 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.
Even after one year of observation the variance in solar distance of the comet is still too small to allow definite brightness parameters. The 114 observations of 25 observers (until start of August 2018) can be best represented by the parameters m0=4.7 mag / n=4, but even the values m0=1.8 mag / n=6 work reasonably well. Due to the temporarily increasing distance comet-Earth the apparent coma diameter decreased from 0.8' to 0.6' in fall 2017. Measuring 1.0' at the opening of 2018 it increased to the maximum of 1.4' during spring 2018. Thereafter it decreased, measuring 1.0' in July. This implies a constant absolute coma diameter of 125.000 km in 2017 and of 190.000 km in 2018. The coma was medium-condensed (DC 4), except in March/April 2018 when it was estimated to be significantly more diffuse (DC 2-3). Between February and May 2018 CCD-observers could detect a 2' (1.5 Mio. km) tail, directed towards SE at first, slowly rotating towards E.

Total Brightness and Coma Diameter

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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 124 observations by 21 observers (until the opening of August 2018) the comet shows an average brightness development, which can be well represented by the formula
m = 5.5 mag + 5×log D + 10.5×log r
Between mid-August and mid-November 2017 the comet brightened from 15.5 mag to 14.5 mag. Between mid-December and mid-April 2018 it brightened further from 14.0 mag to the maximum of 12.5 mag. Due to the fact that the comet will recede from Earth during summer 2018 it will temporarily fade a bit until perihelion, but should reach a second maximum of 12.5 mag in December 2018.
Until the end of 2017 the comet showed a constant apparent coma diameter of 0.5'. Thereafter it increased rapidly, reaching about 1.4' in March, which it holds since. This yields an absolute coma diameter of 90.000 km in 2017, followed by a steady increase to 190.000 km until the start of May 2018, which it holds since. So far the coma is medium-condensed (DC 4). Between February and May 2018 a tail with a maximum length of 2' (1 Mio. km) was reported. This was directed towards SE at first, towards NE at the end of this period.

Total Brightness and Coma Diameter

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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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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 May 21, 2017 the PanSTARRS team discovered a comet of magnitude 21.0 with a miniscule coma in the constellation Draco. Follow-up observations of comet C/2017K2 (PanSTARRS) showed a moderately condensed 12" coma of total magnitude 19.0 (CBET 4393 / MPEC 2017-N26). The comet was detected in the record distance of 16.1 AU, indicating an absolute brightness of 1 mag and an absolute coma diameter of 140.000 km. The comet will reach perihelion at a distance f 1.80 AU not prior to the Christmas days 2022. It should be brighter than 16.0 mag from early 2020 to the end of 2025. During this interval it will move from the northern parts of Hercules through Ophiuchus and Scorpius, diving far south between October 2022 and March 2023, then reappearing for mid-European observers in Eridanus, then moving through Lepus, Orion and Taurus into Auriga. Its maximum brightness of about 5.5 mag should be reached around the turn of the years 2022/23. During the most interesting months it will be observable from mid-European locations in the evening sky until the end of August 2022 (then of magnitude 6.0), then from early September 2023 (then of magnitude 9.5) onwards in the morning sky.

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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 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 3.24 AU not prior to Jan. 15, 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.
Based on only 20 observations (until start of August 2018) only preliminary values can be derived for the brightness parameters: m0=5.8 mag / n=4. Thus the comet should peak at the opening of May 2019 at 13.0 mag. Between May and July 2018 it brightened from magnitude 15.0 to 14.0, showing a significantly condensed (DC 6) coma of 0.7' diameter.

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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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Images, taken by the PanSTARRS project on Oct. 2, 2017 showed a faint comet with a miniscule coma in the constellation Eridanus. Follow-up observertions of comet C/2017 T2 (PanSTARRS) showed a significantly condensed 12" coma of total magnitude 19.3 and a 20" tail in p.a. 290°. The comet will pass perihelion on May 6, 2020 in the distance of 1.62 AU. It is expected to peak at magnitude 8.0 during several weeks (CBET 4445). It should be brighter than 16 mag during the years 2019 and 2020, being brighter than 12.0 mag between October 2019 and October 2020. During the most interesting months it will be better positioned in the morning sky until November 2019 for mid-European observers. Thereafter it will be better observable in the evening sky until the opening of September 2020. During this time interval it will move through the constellations Taurus, Auriga, Perseus, Cassiopeia, Camelopardalis (maximum brightness), Ursa Major, Canes Venatici, Coma Berenices and Virgo.

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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. In July 2018 it peaked at magnitude 9.0. The implyable brightness parameters are approximately m0=9.0 mag / n=4. The diameter of the significantly condensed (DC 5-6) coma was in the order of 3-4'.

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On images taken with the &quto;Asteroid Terrestrial-impact Last Alert System" (ATLAS) on Jan. 10, 2018 an asteroidal object was discovered in the northern part of Virgo. Follow-up observations revealed its cometary nature. Comet C/2018 A3 (ATLAS) showed an 8" coma of total magnitude 18.0. It will pass perihelion in the solar distance of 3.28 AU on Jan. 11, 2019, expected to peak at magnitude 15.0 (CBET 4476 / MPEC 2018-B155). It should be brighter than magnitude 16.0 between November 2018 and February 2019, thereby moving from the central part of Ursa Mayor to the southwestern part of Camelopardalis, thus being observable for mid-European observers during the whole night.

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On Jan. 15, 2018 A.R. Gibbs discovered a 19 mag comet in Leo. Follow-up observations of comet C/2018 A6 (Gibbs) showed a highly condensed, 10" coma of total magnitude 18.8 and a fan-shaped 15" tail (PW=110-17°). The comet will pass perihelion in the solar distance of 2.86 AU on May 24, 2019, expected to peak at magnitude 15 (CBET 4479). However, after the start of 2019 (then 16.0 mag) it will be situated far in the southern sky.

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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 then 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.

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On July 7, 2018 the ASASSN team discovered a comet of magnitude 16 in the central part of Eridanus. Follow-up observations of comet C/2018 N2 (ASASSN) showed a strongly condensed 25" coma and a 15" tail in p.a. 220°. The comet will pass perihelion on Oct. 4, 2019 at a distance of 3.01 AU, expected to reach magnitude 12 (CBET 4534). It should be brighter than 16 mag until the end of 2020. During this interval it moves through the constellations Phoenix, Sculptor, Cetus, Aries, Triangulum, Andromeda (perihelion), Cassiopeia, Camelopardalis and Draco. Thus it will be well placed for mid-European observers during the most interesting weeks.

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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.

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 rapid brightness evolution. Based on 61 observations from 11 observers (until the opening of August 2018) the brightness evolution can be well represented by the formula
m = 5.5 mag + 5×log D + 10.5×log r
This yields a maximum brightness of 12.5 mag in mid-May 2018. At the beginning of the apparition the coma measured 1.1', then increased to 1.6' at the opening of June. This implies a continuous decline of the absolute coma diameter from 110.000 km to 65.000 km during the apparition. The coma was medium-condensed (constant at DC 3-4). No tail was reported.

Total Brightness and Coma Diameter

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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, best observable during the second half of the night.
Only 40 observations from 11 observers came to my knowledge until the start of August 2018. They can only be represented in a plausible manner by applying a time-dependent formula:
m = 12.2 mag + 5×log D + 0.022×|t-T|
This implies a maximum brightness of 12.2 mag in mid-August 2018. The coma diameter increased from short of 0.5' (25.000 km) at the start of the apparition to 1.6' (75.000 km) at the end of July. During this period the coma condensed with the degree of condensation increasing from DC 3 to DC 5-6. A westward-pointing tail was observed in June/July, reaching a length of 5' (1 Mio.km).

Total Brightness and Coma Diameter

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Owner of larger instruments can try to observe comet 59P/Kearns-Kwee (P=9.53a) in fall and winter 2018. It will reach perihelion at a solar distance of 2.36 AU on Sep. 16. During the interval August to November it should brighten from 15.0 mag to 14.0 mag. Thereafter it will fade, reaching 15.0 mag again in March 2019. The comet moves through the constellations Auriga, Gemini and Cancer, thus will be observable in the morning sky during the first months, thereafter during the whole night.

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On Nov. 3, 2018 comet 64P/Swift-Gehrels (P=9.41a) will pass perihelion in the solar distance of 1.39 AU. Between August and November it should brighten from 15.0 mag to 11.0 mag, only to fade in a similar manner thereafter. Between August 2018 and January 2019 it moves through the constellations Pegasus, Pisces, Andromeda, Triangulum, Aries and Taurus, thus will be observable the whole night through.

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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 67 observations from 9 observers (until early August 2018). Based on these, the parameters m0=7.7 mag / n=11 and a maximum brightness of 10.5 mag around May 20, 2018 result. The coma diameter increased from 1.5' (65.000 km) at the beginning of the apparition to the maximum of 6.5' (270.000 km), which was hold constant between the end of May and mid-June. Thereafter it began to decrease, reaching 2,0' (80.000 km) at the end of July. The coma was very diffuse. The degree of condensation remained at DC 1-2 to DC 2 most of the apparition. Only in June was it briefly estimated at DC 3. No tail was reported.

Total Brightness and Coma Diameter

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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.

Total Brightness and Coma Diameter

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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:

pre-perihelion: m = 6.4 mag + 5×log D + 55×log r
post-perihelion: m = 10.0 mag + 5×log D + 15×log r

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 Diameter

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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 11.0 around July 10, 2018. Based on 29 observations by 6 observers the brightness parameters m0=15.0 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. It showed a highly condensed (DC 6), but remarkably small coma which is in line with the low absolute brightness. The coma diameter increased from 0.3' (8.000 km) at the beginning of the apparition to the maximum of 1.2' (18.000 km) at the end of June, only to decrease again to 0.7' (7.000 km) until the first days of August. A tail was observed - visually and via CCD - in June and July, which reached a length of 10' (150.000 km). It was oriented eastward at first, then began to rotate by end of June, pointing south-westerly by end of July.

Total Brightness and Coma Diameter

Andreas Kammerer


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