Comet-seeking on Cold, Crunchy Nights

If you live where it snows you're familiar with the sounds it makes when walked on. In warmer temperatures snow emanates a rumbly krunk-krunk-krunk. As the air gets colder it rises in pitch. Well below zero, snow squeaks loudly and sounds like stepping on Styrofoam.

Comets are composed of ice, dust, and rock at low temperature. Walking on one may be no different from tramping on rocks. But I'd like to think there would be occasional slick spots, clods of dust to kick and loft, and fragile, rotten ice poised to crumble at the slightest toe tap. Granted, it'll be a long time before anyone plants a boot there. But that shouldn't stop us from imagining the possibilities when we point our telescopes toward these winter-season comets the next crunchy, clear night.

Comet Leonard (C/2021 A1)

Comet Leonard (C/2021 A1) has stolen the spotlight the past few weeks with its cyclic outbursts, disconnection events, and spectacular, photogenic tail. On December 29th from dark Atacama desert skies, Daniele Gasparri captured a flocculent 60°-long ion tail that resembled chimney smoke twisting in the wind. Not bad for a 1-kilometer-wide comet that peaked at around 3rd magnitude during its brightest flare-up.

"Parked" for now in the southwestern corner of Piscis Austrinus, Comet Leonard passed perihelion on January 3rd and has faded to magnitude 5.5–6 (January 7th). It still sports a bright coma and faint, east-pointing tail visible in binoculars from a dark sky, but only for observers in the Southern Hemisphere. For the most part it departed northern skies in late December. My last sighting was on Christmas Eve, when Leonard barely came up for air at dusk.

Expect the comet to fade to 10th magnitude by mid-February. If you're able, give it a kiss goodbye — Leonard arrived on a parabolic orbit, but it's leaving on a hyperbolic one and will never ignite a smile again.

Comet 19P/Borrelly

I was happy to kick off the New Year with my first look at this well-known periodic comet during its current apparition. Despite light pollution amplified by a recent snowfall, 19P/Borrelly exhibited a small, well-condensed, 2-arcminute-wide coma in my 15-inch Dob (used for all these observations) at 64× magnification. I applied a Swan Band filter, which enhances the apparent brightness and contrast of gas-rich comets, but saw no change in its appearance.

Comet 19P/Borrelly appears near 2nd-magnitude Deneb Kaitos, also known as Beta (β) Ceti, early this month as it heads northeast from Cetus toward Pisces at slightly less than 1° per day. Hunt for it early in the evening as soon as it gets dark when the comet culminates in the southern sky. Borrelly will hover around magnitude 9–9.5 all month then slowly fade, though it will remain brighter than 11th magnitude through March. Happy news because it will pass just a degree south of the complicated reflection nebula NGC 1333 on March 15–16 and roughly the same distance off the southern coast of the California Nebula (NGC 1499) on March 26–27. These should make good photo opportunities. (See the January 2022 issue of Sky & Telescope for a detailed chart of Comet Borrelly's path this month.)

Comet 104P/Kowal

On January 2.01 UT, after star-hopping from 30 and 33 Piscium, I landed on a large, soft, circular glow about 4′ across with a magnitude of 9.8. Even through light pollution, 104P/Kowal was easy to spot at low magnification (64×), and this time the Swan filter made a difference, increasing the comet's contrast and further brightening the inner coma.

On January 5–6, it crosses from southern Pisces into Cetus moving northeast. Kowal will reach a peak magnitude around 9.5 this month and then fade. Watch it pass just north of 4th-magnitude Alpha (α) Piscium on the night of January 27 — about 8′ as seen from Europe and Africa and 12′ from the Americas.

American astronomer Charles Kowal, who worked at the Mount Wilson and Palomar Observatories, discovered the object in 1979. It's a member of the Jupiter-family of comets, so called because their current orbits are primarily shaped by the gravitational influence of that planet. Kowal passed away in 2011, but his comet returns to the inner Solar System every 5.7 years.

ATLAS (C/2019 L3)

Now at peak brightness with a magnitude of 9.5, this a wonderful little comet is ideally located in Gemini for Northern Hemisphere skywatchers. Don't let its small size fool you. The coma has a high surface brightness and bright, starlike pseudo-nucleus (DC=7 on January 1.05 UT). ATLAS hangs in there between magnitude 9–10.5 through March while slowly arcing southwest across Gemini. On the nights of January 30th and 31th, it passes about 20′ east-southeast of the attractive open cluster NGC 2266.

ATLAS is an acronym for Asteroid Terrestrial-impact Last Alert System and consists of two telescopes 100 miles apart on separate Hawaiian islands that automatically scan the sky several times a night in search of moving objects. To date, the survey has discovered hundreds of Near-Earth and Potentially Hazardous Asteroids, 65 comets, and more than 10,000 supernovae.

Comet 67P/Churyumov-Gerasimenko

"Chury" has staying power, having provided excellent views since the fall. Although fading slowly, the comet continues to shine around magnitude 9.5 in early January as it slides east-southeast across northern Cancer. To find it, start at 4th-magnitude Iota (ι) Cancri, a beautiful and colorful double star (magnitudes 4.2, 6.6; separation 30″). Comet 67P passes less than ½° north of this gem on January 15th.

On January 2.23 UT, I observed a 2.5-arcminute-wide, moderately condensed coma (DC=5) with a brighter, fuzzy false nucleus and a lovely, faint tail about 12′ long pointing west. Medium magnifications of around 100× help to bring out this dusty streak best.

Thanks to the incredibly detailed images returned by the European Space Agency's Rosetta Mission we can easily imagine 67P's funky bilobate shape, dust jets, and collapsing cliffs any clear January evening.

PanSTARRS (C/2017 K2)

Observing this highly anticipated comet means getting up early. I observed it just before the start of morning twilight low in the eastern sky in Ophiuchus on January 2.50. It appeared small — about 1.5′ across — and moderately compact with DC=5 and a magnitude of 11.8. That sounds faint until you realize that K2 is currently 5.1 a.u. from the Earth, nearly the same distance as Jupiter is from the Sun.

Its distance decreases while it slowly brightens for the remainder of the year. After heading east across Ophiuchus, it crosses into Aquila in early March, does a tight, slow turn, and exits the constellation on May 10th. Picking up speed, K2 angles southwest across Ophiuchus and brightens up to magnitude 8–8.5 during the summer. On July 15th, it passes ½° northwest of the bright globular cluster M10.

The comet dives into evening twilight by September for northern viewers, but Southern Hemisphere skywatchers will be able to follow it to its December 7th perihelion and beyond. Although the comet will be rather low in Ara and Pavo, it may reach 6th magnitude when brightest in late December and early January 2023.