Last updated: September 2, 2020

For planning purposes, on this page I will list the incoming comets that are expected to become moderately bright or otherwise notable within the next one to two years, and which I expect to add to my tally (if I haven't already). I don't intend this list to be exhaustive, but instead will focus on those comets that are worthy of attention from sky-watchers and other interested people (including, certainly, students) who would not normally be considered "comet astronomers." I plan to update this page every one to two months and/or as necessary.

The "long-range" comets listed at the end of this page are, as implied, mentioned here primarily for long-range planning purposes.


COMET NEOWISE C/2020 P1      (Perihelion 2020 October 20)

Following on the heels of the borderline-"Great" Comet NEOWISE C/2020 F3 (no. 676), the NEOWISE mission discovered another small-perihelion distance comet (0.34 AU) on August 2. The comet is presently around 16th magnitude and is deep in southern circumpolar skies (current declination -73 degrees), and remains exclusively accessible from the southern hemisphere up until almost the time of perihelion passage. After passing 11 degrees due west of the sun just before perihelion it becomes accessible in the northern hemisphere's morning sky during the latter part of October, although the elongation remains somewhat small for the next few weeks. Theoretically, the comet could become somewhat bright -- possibly reaching naked-eye brightness -- around perihelion and/or afterwards, although at this time it seems to be rather faint intrinsically, and thus how bright it might actually get, and even whether or not it survives perihelion, are things we will have to see over the coming weeks.

UPDATE (September 2, 2020): Comet NEOWISE remains in southern circumpolar skies for the time being but by this writing has traveled northward to declination -61 degrees; it continues in its northward travel during the coming weeks. So far there have been no reports of visual observations from the southern hemisphere; the brightest CCD magnitudes (from late August) indicate a brightness near 15th magnitude.


COMET 11P/TEMPEL-SWIFT-LINEAR      (Perihelion 2020 November 26)

This rather famous comet was lost for almost a century, but was finally re-discovered by the LINEAR program in late 2001. It has remained a dim and distant object since that time, however a moderately close approach to Jupiter in 2018 decreased the perihelion distance somewhat and the viewing geometry in 2020 is quite favorable, with the comet's being at opposition in mid-September and passing 0.49 AU from Earth in early November. There haven't been any visual observations of this comet in over 100 years and thus it is difficult to know what to expect, but hopefully the favorable viewing conditions might allow it to become visually detectable.


COMET 141P/MACHHOLZ 2      (Perihelion 2020 December 15)

Prior to this comet's discovery return in 1994 (no. 193) it fragmented into several pieces, some of which were visually detectable during that return (with the primary component becoming as bright as 7th magnitude). The secondary components have all faded away since then -- although the brightest one was still visually detectable for a while during the 1999 return (no. 273) -- and the primary itself has faded quite a bit, appearing as only a vague, diffuse object of 12th magnitude in 2015 (no. 581); meanwhile, a new faint component was detected in CCD images during that return. The viewing geometry for the 2020 return is moderately favorable, with the comet's passing 0.52 AU from Earth in mid-January 2021; how bright the primary component might become, and whether or not any other components might be present, remains to be seen.


COMET 7P/PONS-WINNECKE       (Perihelion 2021 May 27)

This long-known comet has a rather storied history, which includes a series of close approaches to Earth during the early decades of the 20th Century, although since it has been perturbed into a larger orbit it can no longer make such approaches. The 2021 return is the most favorable one it will have had in several decades, with a minimum distance from Earth of 0.44 AU taking place in mid-June, and it should reach 10th or 11th magnitude. It has already been recovered as a very faint object in early January 2020.


COMET 6P/d'ARREST      (Perihelion 2021 September 27)

After its favorable return in 2008 (no. 435) I missed this comet entirely during its unfavorable return in 2015, although apparently some observers in the southern hemisphere managed to detect it as a faint object. The return in 2021 is moderately favorable, similar to that of 1982 (no. 51) during which it reached close to 9th magnitude. The comet remains in the evening sky, at a somewhat high southerly declination (-20 degrees to -30 degrees) throughout the course of the apparition.


COMET 67P/CHURYUMOV-GERASIMENKO      (Perihelion 2021 November 2)

After its rather mediocre return in 2009 (no. 444) this comet returned again, under slightly better but still mediocre circumstances, in 2015 (no. 577), and reached 12th magnitude. This was the return where it was visited and studied by ESA's Rosetta mission, and I discuss this in detail in the comet's "Ice and Stone 2020" "Comet of the Week" presentation. The viewing geometry for the return in 2021 is very favorable, similar to that of 1982 (no. 53) where it reached 9th magnitude and I could detect it with 10x50 binoculars and see some dramatic tail structure telescopically. The comet remains well placed for observation for several months and is closest to Earth (0.42 AU) a week and a half after perihelion passage.


COMET 19P/BORRELLY       (Perihelion 2022 February 1)

I've managed to observe this comet at all of its recent returns, including the mediocre one in 2008 (no. 436) and the very unfavorable one in 2015 (no. 585), when I saw it a couple of times as a very faint object over four months past perihelion. The 2022 return is the best one it will have had in over two decades, being somewhat similar to its return in 1981 (no. 43), the first time I observed it and during which it reached 10th magnitude. The comet is deep in southern skies (declination south of -50 degress) until early November 2021 and should become visually detectable from the southern hemisphere during that period; it comes northward after that and I expect to pick it up in the evening sky before the end of 2021 and be able to follow it until April or May 2022.





COMET PANSTARRS C/2017 K2     (Perihelion 2022 December 19)

Despite being located at a heliocentric distance of 16.1 AU, this comet was clearly active, and a relatively bright 19th to 20th magnitude, when discovered in May 2017. Even more remarkably, in pre-discovery images taken as far back as May 2013, the comet is clearly active even at a heliocentric distance of 23.7 AU. The high intrinsic brightness, and high activity level at such large distances from the sun, is somewhat reminiscent of Comet Hale-Bopp C/1995 O1 (no. 199).

Unfortunately, the comet's perihelion distance is still a relatively large 1.80 AU. Even more unfortunately, the comet is on the far side of the sun from Earth at the time, never coming closer than 2.23 AU. While naked-eye visibility, perhaps even conspicuous naked-eye visibility, would seem to be almost a certainty, the comet is unlikely to become "Great."

And even more unfortunately for northern hemisphere observers, the comet is in southern circumpolar skies at the time of perihelion. Indeed, the comet is inaccessible from the northern hemisphere for almost a full year (September 2022 through August 2023).


Comet PANSTARRS C/2017 K2 (small diffuse object in center) as imaged on March 6, 2018, by the Las Cumbres Observatory facility at McDonald Observatory in Texas. At the time this image was taken, the comet's heliocentric distance was 14.4 AU.
COMET 12P/PONS-BROOKS     (Perihelion 2024 April 21)

This "classical" Halley-type comet (period 70 years) last returned in 1954, four years before I was born. The viewing geometry in 2024 is, unfortunately, rather unfavorable, as during the run-up to perihelion the comet remains on the far side of the sun from Earth and is only visible for a brief period of time in the northwestern sky after dusk, at a small elongation (37 degrees in mid-March, shrinking to 28 degrees by month's end and to 23 degrees by perihelion). Despite the poor viewing geometry, the comet is intrinsically rather bright, and should reach a peak brightness close to 5th magnitude. After perihelion the comet travels southward and is visible from the southern hemisphere as it recedes and fades.

UPDATE (June 28, 2020): Comet Pons-Brooks was recovered on June 10, 2020 -- almost four years before perihelion passage -- by a team of astronomers led by Matthew Knight utilizing the Lowell Discovery Telescope in Arizona (with confirming images obtained on June 17). The comet's heliocentric distance at the time of its recovery was 11.93 AU, and it appeared as a very faint object near 23rd magnitude, with a short tail indicating that it is already active.


COMET 13P/OLBERS     (Perihelion 2024 June 30)

This other "classical" Halley-type comet (period 68 years) last returned in 1956, two years after the above comet and two years before I was born. Also as with the above comet, the viewing geometry remains relatively poor, with the comet's remaining on the far side of the sun from Earth; on the other hand, it is almost identical to the viewing geometry in 1956. It remains in the northern hemisphere's evening sky throughout the period of prime visibility, albeit at a small elongation (dropping below 30 degrees in early May, to a minimum of 25.5 degrees in early June before increasing back to 30 degrees by perihelion to a maximum of 39 degrees in August). Based upon the reported brightnesses in 1956, the comet should reach a peak brightness between 6th and 7th magnitude.

Around mid-April 12P/Pons-Brooks and 13P/Olbers will be located some 15 degrees from each other, the latter comet being higher (to the east and north) of the former one.


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