If you like chasing comets, here’s a guide to this year’s best and brightest.
Looking at deep-sky objects through a telescope has always felt a bit like going to a museum and admiring a famous painting. You return again and again to find new ways to appreciate a work of art that itself never changes. Comets are different. You have to run to keep up. Not only does your own perspective deepen over time but the object (artwork) never stops evolving. There is exactly one Mona Lisa and one Beehive Cluster, but a comet may have a hundred guises. We're compelled to keep returning to see what's up.
With that in mind let's look at the year's best and brightest comets — those reaching 10th magnitude or better. Of course, given their drop-in-anytime nature a new one could show up on Earth's doorstep next month. Surveys discover dozens of fresh comets each year though the great majority are too faint to see in amateur telescopes.
Most of 2024's best are predicted returns of periodic comets, denoted by the prefix "P." Two are fairly recent discoveries and designated with the letter "C" for non-periodic comets with orbital periods greater than 200 years. Distances are given in astronomical units or a.u., the average distance between the Earth and Sun.
Perihelion: April 21 (0.8 a.u.) / Orbital period: 71.3 years
Closest approach to Earth: June 2 (1.6 a.u.)
Best viewing window: At nightfall, February through mid-April. Also visible just before dawn in February.
Expected peak magnitude: 4 in early April
With its frequent outbursts 12P/Pons-Brooks is a must-see every clear night. It most recent flare — the seventh during the current apparition — occurred on January 18th when the comet brightened by more than a magnitude (visually) inside of 24 hours. When in outburst, the nuclear region appears very bright and compact in contrast to the rest of the coma.
Currently, the comet hovers around 8th magnitude as it creeps westward from Cygnus into Andromeda over the next month. Catch it just after dusk for the best view. Through my 15-inch Dob at 67× on the night of January 29th Comet 12P exhibited a well-condensed, brighter nuclear region centered in a fainter 5′-diameter coma. I got all happy when I made out a short, faint tail pointing north — my first tail-sighting of the current apparition.
The comet will continue to brighten into early spring, reaching 6th magnitude in mid-March as it treks from Andromeda to Pisces. At the same time, it slowly loses altitude. When at peak brightness in mid-April it will be fighting twilight. Fortuitously, Jupiter shines within 5° or about one binocular field of 12P from April 9–16, providing observers with a great reference point for locating it low in the west at dusk.
There's been much talk, hype even, about seeing the comet during April's total solar eclipse. But given that it will lie about 25° from the Sun and assuming it keeps to 4th magnitude I don't think we'll spot it with the naked eye. Cameras and special processing software may do better. Again, Jupiter offers a helping hand, pointing the way to the comet located 6° to its west. However you observe 12P you can participate in an ongoing study of its behavior. Check out the details at the Comet Chasers website.
Perihelion: January 25 (1.4 a.u.) / Orbital period: 7.5 years
Closest approach to Earth: December 12, 2023 (0.6 a.u.)
Best viewing window: Nightfall to midnight from February through March
Expected peak magnitude: 9.5 in early February
Looking for another evening comet to observe after 12P/Pons-Brooks? Check out 144P/Kushida discovered by Japanese amateur Yoshio Kushida in 1994. It's about as bright as it's going to get and with the Moon out of the sky, timing is just right. Comet 144P will pass about 0.3° southwest of Aldebaran on February 9th and 0.5° east of the star the following night. Point your scope at the star and you're there!
My best view came on January 29th just as the downy dust bunny grazed a 7th-magnitude star. Despite the glare I could still made out a 10.0-magnitude, moderately condensed coma 3′ across. A Swan Band filter, which enhances blue-green diatomic carbon emissions in comets, improved visibility and expanded the coma diameter to 4′.
Perihelion: December 25, 2023 (1.3 a.u.) / Orbital period: 6.2 years
Closest approach to Earth: January 29 (0.5 a.u.)
Best viewing window: Midnight till dawn from February through March
Expected peak magnitude: Currently past peak but 8.5 in early February
Although 62P/Tsuchinshan peaked in early January around 8th magnitude it's still going strong as February opens. When seeking the comet be aware it's a large, diffuse object. When I viewed it on January 18th before dawn, the coma measured some 7′ across with a lightly compacted core. As with 144P/Kushida a Swan Band filter will improve this gassy object's visibility. Comet Tsuchinshan traces a narrow loop smack-dab in the middle of the Virgo Galaxy Cluster for the next two months, making it a perfect steppingstone to a host of bright galaxies in the region.
Perihelion: May 1, 2019 (5.8 a.u.) / Orbital period: 14.7 years
Closest approach to Earth: September 9, 2018 (4.8 a.u.)
Best viewing window: Evening sky from February through April
Expected peak magnitude: Erratic, as bright as 10 during outbursts
Almost as much fun to observe as 12P/Pons-Brooks, 29P/Schwassmann-Wachmann experiences similar multiple flares each year as warmed, dust-laden gas trapped within its core races through subterranean caverns until venting from a surface fissure. When undergoing a bright outburst, it's visible in a 6-inch telescope despite being as remote as Jupiter. During quiescence the comet is only dimly visible in large amateur instruments. I haven't kept a scorecard, but I bet I've seen at least 40 eruptions since my first in 1989. They can occur multiple times a year. Keep an eye on Comet 29P this season as it loops through Cancer about 5° northwest of the Beehive Cluster.
Comet PanSTARRS (C/2021 S3)
Perihelion: February 14 (1.3 a.u.)
Closest approach to Earth: March 14 (1.3 a.u.)
Best viewing window: Morning sky from February through April
Expected peak magnitude: 9.5 in early February
Northern Hemisphere comet-watchers have been chomping at the bit for a look at the latest PanSTARRS comet. I'm happy to report it recently swam into visibility not far from Antares in Scorpius and is now accessible shortly before dawn in the southeastern sky. Comet C/2021 S3 displays a tadpole-like tail I'm eager to get my eyes on once the Moon departs the scene. Over the next few months, the comet will slowly fade as it bears northeast straight up the band of the summer Milky Way.
Perihelion: June 30 (1.2 a.u.) / Orbital period: 69.5 years
Closest approach to Earth: July 20 (1.9 a.u.)
Best viewing window: Evening sky from May through August
Expected peak magnitude: 7.5 in early July
With a period of almost 70 years most of us will see 13P/Olbers just once in this lifetime. In early February it's a faint, 14th-magnitude speck in Eridanus slowly tracking northwest. Come mid-April watch it glide midway between the Pleiades and Hyades at a beefier 10th magnitude. The infrequent visitor continues to brighten through May and June but at the expense of declining altitude. By late May, when it reaches 8th magnitude (binocular range), Comet 13P sits low in the northwestern sky in Auriga at nightfall. Telescopes will reveal a well-developed coma and east-pointing tail.
During the best segment of its apparition 13P/Olbers keeps low in the northwestern sky at twilight's end with an altitude of less than 20° from June through early August. To make the most of its brief visit find a site with an unobstructed horizon and pack mosquito repellant. Dusk is when our whiny friends are hungriest! Southern Hemisphere observers will get their best look at 13P starting in mid-August.
Comet Tsuchinshan-ATLAS (C/2023 A3)
Perihelion: September 27 (0.4 a.u.)
Closest approach to Earth: October 12 (0.5 a.u.)
Best viewing window: Very low before sunrise in late September then at dusk / nightfall mid-October through November.
Expected peak magnitude: 0.5 at dawn; 1–1.5 at dusk
The year's most highly anticipated comet is just now coming into view in the morning sky. I got my first look at Comet Tsuchinshan-ATLAS on the morning of January 20th. At 142× in the 15-inch it was a small, well-condensed object with a near-stellar pseudo-nucleus. Although only magnitude 13.6 and ~25″ across its compactness made for a fairly easy catch. I find a lot of enjoyment in spotting a comet early on when it's still a "baby" and watching it mature into an adult.
Comet C/2023 A3 remains relatively faint as it travels northwest from Libra into Virgo and gradually transitions into the evening sky. By late May it should reach 10th magnitude and come within reach of 6- to 8-inch telescopes. In early July the comet hovers low in the west at nightfall in Leo around 8.5 magnitude. From mid-July through mid-September, it's lost in the solar glare even as the comet swells to 2nd magnitude. Conditions improve a bit during the final week of September when C/2023 A3 hits 1st magnitude low in the eastern sky at dawn. Then is quickly circles back toward the Sun. Southern Hemisphere skywatchers will fare better at this time with the comet visible near peak brightness low in the eastern sky in early morning twilight through about October 4th.
After another tangle with twilight, Comet Tsuchinshan-ATLAS resurrects itself again, returning to view at dusk around October 12th low in the western sky. It should glow around 1st magnitude at this time with a substantial, east-pointing tail. It may even hit 0 magnitude if it turns out to be a dusty comet. Comet C/2023 A3 quickly distances itself from the Sun. By October 14th we'll see it in a dark sky, albeit very low, as it climbs from Virgo into Serpens. Solar elongation and altitude increase quickly but the comet dims just as fast, dropping about three magnitudes in the next two weeks.
Anything can happen with a new arrival from the Oort Cloud like Tsuchinshan-ATLAS but assuming it doesn't crumble to pieces it will become an obvious naked-eye sight in late September through mid-October.
Perihelion: November 29 (1.1 a.u.) / Orbital period: 8.7 years
Closest approach to Earth: December 9 (0.5 a.u.)
Best viewing window: Morning sky in early December, circumpolar in mid-December and evening sky in late December
Expected peak magnitude: 10
One remaining periodic comet livens up the final months of 2024. Discovered in 2007, Comet 333P/LINEAR, will be making its first predicted return to Earth's vicinity. In December when brightest the comet travels from Canes Venatici through Ursa Major and Draco and into Cygnus. For much of the month it's a circumpolar object for mid-northern-latitude observers.
Get your maps here!
To track these eight visitors you'll need maps. Each link below will pop open a map of the selected comet's path during the brightest portion of its apparition. All were created with MegaStar, courtesy of Emil Bonanno. The maps vary in detail depending on how long a comet is visible and how much sky it covers. In future posts I'll share more detailed charts.
You can also use stargazing apps such as SkySafari or Stellarium to plot daily positions or on the Web at In-the-sky.org. To keep up on the latest comet news check Seiichi Yoshida's excellent Weekly Information about Bright Comets, the Comet Observation Database and Gideon van Buitenen's Visual Comets. The latter includes links to the latest orbital elements for downloading into software packages. Happy hunting!
- PanSTARRS (C/2021 S3)
- Tsuchinshan-ATLAS (C/2023 A3)
Read more on current celestial events in the February 2024 issue of Sky & Telescope.