Catch these Comets in 2018

We look ahead to see what fuzzy visitors, newly-discovered or returning, will brighten the nights ahead. One and possibly two naked-eye comets are on the way.

Surprise No. 1

Comet PanSTARRS (C/2016 ER61), photographed here on May 2, 2017, became one of the brightest comets of 2017.
Damian Peach

Comet chasers stayed busy in 2017 with at least 16 comets brighter than magnitude 13.5. These included three brand new discoveries: Lovejoy (C/2017 E4), the sixth find by Australian amateur Terry Lovejoy; ASASSN1 (C/2017 O1 ASASSN) and Heinze (C/2017 T1).

The enigmatic "rock comet" 174P/Echeclus surprised and delighted with a bright outburst in December that put it within range of an 8-inch scoipe under dark skies, while the ever-fitful 29P/Schwassmann-Wachmann provided a half dozen flare-ups that kept us on our toes.

My notes show no naked-eye comets for 2017 — at least from my observing site — but both 41P/Honda-Mrkos-Pajdusakova and PanSTARRS (C/2015 ER61) came close at magnitude 6.2 in January and April respectively. These, along with four others, made for a total of six binocular comets, depending on your instrument and sky conditions.

One rockin' comet!

A shell of gas and dust envelops the nucleus of Comet 174P/Echeclus during its December 2017 outburst.
Damian Peach / Chilescope Team

The new year opens with four modest comets, all in the 10th-magnitude range, schlepping about about the night sky: dim ASASSN1 (C/2017 O1) still at Polaris's side; PanSTARRS (C/2016 R2) with its free-form, ever-evolving tail; Heinze (C/2017 T1) zipping across the northern evening sky; and 62P/Tsuchinshan, on the fade in Virgo.

In the coming year at least one and possibly three comets may reach naked-eye level with five or six bright enough to see in binoculars. Comet 46P/Wirtanen is the most highly anticipated — it's expected to crest at magnitude 4 in a picture-perfect location alongside the Pleiades and Hyades in December. The key word is expected. You know comets as well as I do, and they don't like to be tied down by our expectations. Expect flare-ups, fades, contrary light curves, and even dissolution of these highly volatile objects.

Read on for a guide to comets predicted to peak at magnitude 10.5 or brighter in 2018.

Heinze (C/2017 T1)

Winter visitor

The 10th-magnitude Comet Heinze (C/2017 T1) stands highest at nightfall this month. Positions are marked daily at 0h UT (subtract 5 hours for Eastern Standard Time; 6 for Central; 7 for Mountain; and 8 for Pacific). South is up and stars are plotted to magnitude 8. Click this map and the others to download full-resolution versions for use at the telescope.
SkyMap with additions by the author

Currently about magnitude 10 with a 4′ coma and faint, south-pointing tail, you'll find Heinze winging from Cassiopeia into Lacerta in the coming week. At 1h UT on January 5th, it was a diffuse puff of magnitude-9.8 light with a degree of condensation (DC) of 3 on a scale from 0 (totally diffuse) to 9 (completely stellar) through my 15-inch. The comet is expected to slowly fade but remains visible in the evening sky through mid-February.

PanSTARRS (C/2016 R2 )

Twisty tail

PanSTARRS (C/2016 R2) passes just 18′ west of Gamma (γ) Tauri on January 5th. This particular PanSTARRS discovery has displayed an unusually blue and twisty tail this winter.
Chris Schur

Documenting the corkscrew twists and turns of the tail of PanSTARRS (C/2016 R2) and the comet's unusual blue color has held the attention of astrophotographers in recent weeks. Sign up to the comet mailing list for more details and photos. Visually, the tail is barely detectable, but an 8-inch or larger telescope will show a nice 10.4-magnitude patch of haze about 4′ across with a DC = 3. The comet's quite easy to find with ample naked-eye stars nearby: it crossed the Hyades a week ago and will pass just 2° northwest of the Pleiades at the end of the month. It appears that C/2016 R2 is unusually rich in frozen carbon monoxide (CO), which when ionized by ultraviolet sunlight, fluoresces blue.

Midwinter visitor

Comet PanSTARRS (C/2016 R2) is well-placed in Taurus in the company of the Hyades and Pleiades. It should remain visible all winter as it slowly fades. Stars plotted to magnitude 9.5 with positions marked every 3 days.
SkyMap with additions by the author


Dawn glider

Comet 62P/Tsuchinshan plods through Virgo this month and next. The comet culminates in mid-January around 6 a.m. local time. If you're up early before work, give it a look. 
SkyMap with additions by the author

I've seen a wide range in magnitude estimates for this one in recent days. Some observers peg it at magnitude 11.7, others a magnitude brighter. Amateur Scott Harrington even caught it in 8×56 binoculars at magnitude 10.3 on December 28th. Either way, it's a tailless, weakly condensed blob. As the Moon wanes and then departs the morning sky later this week, we'll soon be able to see "what's up" with 62P/T. It culminates in central Virgo around 6 a.m. local time and creeps eastward, slowly fading over time.

PanSTARRS (C/2016 M1)

Flying by the Globulars

Comet PanSTARRS (C/2016 M1) brightens from magnitude 10.5 in early May to 9.0 by late June as it swings from southern Aquila to the tail of Scorpius. Stars are shown to magnitude 8 with positions marked every 3 days. 
SkyMap with additions by the author

Let's hope a new comet's discovered soon or it's gonna be a long winter and spring! Comet-quietude descends until May when Comet PanSTARRS (C/2016 M1) comes to the rescue. It's presently in the pre-dawn sky in Ophiuchus at magnitude 13 and won't crack magnitude 10.5 until early May. Thereafter it picks up speed, traveling from Aquila into Sagittarius. By the summer solstice, it's racing across Corona Australis and enters Ara in early July, when it will be out of view for observers in the northern states. The comet shines brightest at magnitude 9–9.5 through much of June and July and may be visible in binoculars under dark skies.

PanSTARRS (C/2017 S3)

Wild card comet

Comet PanSTARRS (C/2017 S3) could teeter at naked-eye brightness before it's overwhelmed by dawn light . . . or it may become much brighter. This map covers its progress as it rapidly brightens from magnitude 10.2 in Auriga to 5.0 in Cancer in mid-summer. Stars are shown to magnitude 7.5 with positions marked every 3 days.
SkyMap with additions by the author

This one's a wild card. It starts its run at magnitude 10.5 in mid-July, well placed in the morning sky in Camelopardalis. As it scurries east through Auriga and Gemini C/2016 S3 quickly becomes a binocular object at magnitude 7. Even as it brightens rapidly, possibly reaching 6th magnitude on August 7th on its way to perihelion (August 16th), dawn encroaches. We'll probably get our last views when it passes Castor and Pollux on August 4–5 before twilight and daylight finish it off. Thereafter the comet remains near the Sun and rapidly fades from view.

The scenario I just described is based on the most recent orbital elements used by several computer programs and comet sites, but I always crosscheck with JPL's HORIZONS database, which provides detailed ephemerides for many comets. Imagine my surprise when HORIZONS offered an entirely brighter picture. It shows C/2017 S3 at magnitude 5.5 in mid-July, –0.1 in the first days of August, and peaking at –4.6 at perihelion. Holy comas, Batman! If this plot version plays out, the comet may briefly be visible in daylight through a properly shielded telescope.


Cluster crasher

Comet 21P/Giacobini-Zinner slices across Cassiopeia brightening from magnitude 9 to 7 from August through early September. On September 10–11, it crosses the bright open cluster M37and glides by M35 on September 15–16. Stars are shown to magnitude 7.5 with positions marked every 3 days.
SkyMap with additions by the author

Expect an excellent apparition of this well-known returning comet and parent of the Draconid meteor shower. Watch for 21P/G-Z to reach magnitude 10.5 in the early July evening sky near the Cygnus–Cepheus border. At the time of the August Perseid shower, it will have swelled to magnitude 8 in Cassiopeia. Peak brightness of 7th magnitude occurs in September when the comet crosses Auriga and Taurus and stands high in the pre-dawn sky. This comet will make an ideal target for sidewalk astronomy gatherings in mid-summer. G-Z drops south in fall but remains brighter than 10.5 magnitude through mid-November, when it finally "bows out" in Puppis.


Friend of the Hunter and Twins

Comet 38P/Stephan-Oterma will be easy to find just north of Betelgeuse in early October. A month later it peaks around magnitude 9 in eastern Gemini, all the while well-placed in the pre-dawn sky. Stars are shown to magnitude 7.5 with positions marked every 5 days. 
SkyMap with additions by the author

Long time no see! The 38th comet to have its orbit determined also takes 38 years to orbit the Sun. Discovered in 1867 and last seen in 1980, those of us who missed it then (yeah, yours truly) will finally get a second chance. It's predicted to be a fine apparition with the comet entering the stage 5° north of Betelgeuse in Orion at magnitude 10.5 during the first week of October. Come late November, it peaks around magnitude 9 in Gemini near Castor and Pollux and may be visible in binoculars. 38P remains brighter than magnitude 10.5 through New Year's Day 2019.


In bright company

Let the Andromeda Galaxy and the bright open cluster NGC 752 be your guides when it comes to finding 11th-magnitude 64P/Swift-Gehrels this fall. Stars are shown to magnitude 10 with positions marked every 3 days.
SkyMap with additions by the author

I'm cheating a little on this one only because I have a soft spot for periodic comets. Originally discovered in 1889 by the American astronomer Lewis Swift, 64P rounds the Sun every 9.2 years. This time around it hangs out in the vicinity of Beta (β) Andromedae from late October through late November when it's brightest at magnitude 11. Not only is it well placed in the evening sky, the bright star will serve as a sweet guidepost.


Comet rocket takes off!

Look at that comet move! The year ends with a bang as 46P/Wirtanen makes one of its closest approaches to Earth and brightens from magnitude 6 in mid-November to 3 or 4 in mid-December while racing from Fornax to Auriga. Stars shown to magnitude 5 with positions marked every 3 days.
SkyMap with additions by the author

Dessert comes last so don't spoil your appetite. Comet 46P/Wirtanen begins its apparition (magnitude 10.5) along the Cetus–Fornax border in the late September morning sky. Before heading north, it slips further south, reaching declination –33° on November 1st but pumping up to magnitude 7, within easy binocular range. About mid-November, 46P launches straight north with ever-increasing speed, rocketing in brightness and altitude until it towers in Taurus in all of its 4th-magnitude glory two weeks before Christmas. Comet 46P's exceptionally close approach to Earth of 11.5 million km on December 16th could mean several weeks of naked-eye visibility from dark skies.

Comet Wirtanen is intrinsically bright, comes closest to our planet just four days after perihelion, and remains visible all night, making this an exceptional apparition. That's why it's the focus of the Planetary Science Institute's 4*P Coma Morphology Campaign.

Not that I want to throw comet dust on your parade, but HORIZONS offers a slightly different scenario, showing the comet's brightness peaking at magnitude 7.6. Should 46P only manage binocular brightness, it would only be asserting its individuality, something we've come to expect from these icy characters.

For visual observers and astrophotographers, the late fall and early winter season will be a great time to visit with "old friends" with no fewer than four periodic comets visible simultaneously — 21P, 38P, 64P, and 46P. Happy hunting!

For more information on upcoming comets, check these sites, too:

9 thoughts on “Catch these Comets in 2018

  1. Tom-Reiland

    I have observed all but three of these comets. Several in the past few months and the three periodic comets several times. I haven’t tried for PANSTARRS 2016 M1 and 2017 S3 yet, but I did try for Heinze last night with no luck. If it is very small and diffuse as you pointed out, I probably did not have a chance to locate because of its appearance and the observing conditions in Western Pa. The few images that I have seen of it show a very sad looking comet. I’ve read recent magnitude estimates for it ranging from 9.5 to 12.5 magnitude. It certainly didn’t turn out to be what some astronomers had hoped for. Transparency was variable here, with it reaching good at best. (3+ on a scale from 1 to 5, with 5 as the best). Seeing was poor at 2 to 2- for both seeing and steadiness. This might be my last at the 21″ Scope for January thanks to another bad weather system moving in. From my records for 45 years of observing, January is the worst month of the year. Seldom do I get more than 1 or 2 nights viewing with any of my or Wagman Observatory’s scopes. July through October are usually the best months for Astronomy here. December, through February are the worst. Looking forward to warm weather observing, though last night was mild for this time of the year with temps in the mid 40s F.

  2. RussRuss

    Hi Bob,
    Thanks for the interesting article about current comet prospects. That undoubtedly took a lot of research. When weather and moon light permit, I’l give some of these a try. Over the years I’ve been privileged to see over two dozen comets. These have been recorded in either my visual observing log or in photographs on film or by digital means. My observations are chronicled in the following link:

    So looking back into my master spreadsheet-database of visual observations, I found one entry for Comet 38P/Stephan-Oterma. That record of the observation with my home-made 8-inch reflector shows just this for December 29, 1980:

    “Fuzzy object near M36, no tail present”

    Hopefully this time around I’ll get to see more than just a fuzzy object. If not for Stephan-Oterma, then maybe some of the other comets. And who knows what as yet unknown incoming cometary spectacle is on the way.

    1. Bob KingBob King Post author

      Thank you, Russ! It’s so fun to see a comet a more than one return, so I know you’ll be looking forward to another visit from 38P. Circumstances change at each apparition, so we really know a comet in terms of behavior, brightness and appearance over time. I look forward to re-observing favorite periodic comets like 2P/Encke, 29P/SW1 and many others.

  3. Lorna

    Can we please get the IAU to change how comets are named? The endless lists of Comet PanSTARRS and other comet hunting systems has resulted in the names becoming irrelevant. Surely a better idea would be if the discovery is made by PanSTARRS or a similar comet hunting system, then the comet is given a name from a list of the names of the team members. If we get a magnificent comet as spectacular as Hale-Bopp sometime soon, new observers could be put off by the confusing name, especially if there is a second Comet PanSTARRS around.

    1. Bob KingBob King Post author


      No question about it, PanSTARRS comets are everywhere. I like your idea — it would be far easier to tell one comet from another using a team member name. There would still be multiple (but fewer) names however, since there are so many PanSTARRS discoveries. Whenever I’m talking comets with other observers I typically drop the PanSTARRS part after a while and just refer to them as “R2” or “ER61” to distinguish one from another. I know – that sounds even worse!

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