Last updated: September 24, 2019

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 2I/BORISOV I/2019 Q4      (Perihelion 2019 December 8)

This comet, discovered by Crimean amateur astronomer Gennady Borisov on August 30, 2019, has turned out to be one of the most important comets ever discovered; with an orbital eccentricity of 3.4 it is clearly an interstellar comet, the first confirmed example of such an object. At present it is located in Cancer, low in the eastern sky before dawn, and according to recent reports, as well as a Las Cumbres Observatory image I took a couple of mornings ago, is close to 17th magnitude.

Brightness predictions are especially problematical for this comet, since there is no precedent to go on. I am cautiously optimistic that it might become visually detectable at perhaps 14th magnitude around the time of perihelion in early December up through the time of its closest approach to Earth (1.94 AU) late that month. By that time it will be starting to get a bit low in my southern sky, and it will permanently drop below my southern horizon by the latter part of January 2020.

NOTE ADDED SEPTEMBER 24, 2019: The IAU's Minor Planet Center has now formally assigned the designation "2I" to this comet to reflect its interstellar origin. I have modified the above designation accordingly.


COMET 289P/BLANPAIN      (Perihelion 2019 December 20)

A lot of mystery surrounds this comet, which was lost between its original discovery in 1819 and its accidental re-discovery (as an asteroid) in 2003; it has exhibited some sporadic cometary activity (including at least one outburst) since that time. It passes 0.09 AU from Earth on January 10, 2020, and will be well placed for observations from the northern hemisphere around that time; indeed, it is favorably placed throughout its entire return to perihelion. Depending upon what level of activity it exhibits, it might -- or might not -- become somewhat bright..


COMET 2P/ENCKE      (Perihelion 2020 June 25)

I have observed this famous comet on a dozen returns going back to 1970, most recently in 2017 (no. 610); I discuss it in my entries for its 2007 return (no. 402) and its 2013 return (no. 531). I will almost certainly not be observing it in 2020; it is impossibly placed for observation from the northern hemisphere prior to perihelion but does become accessible in the evening sky for southern hemisphere observers during the first half of July, where it should remain visually detectable for perhaps a month or so before fading out. The viewing circumstances for the northern hemisphere are much more favorable during the subsequent return to perihelion in October 2023.


COMET 88P/HOWELL      (Perihelion 2020 September 26)

The viewing geometry for this comet's 2020 return is quite similar to -- in fact, slightly better than -- the return in 2009 (no. 457). At that return the comet reached close to 9th magnitude and on a couple of occasions I could faintly detect it with binoculars; I would expect something similar this time around.


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 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.


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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