Astro Bob: Winter encounters with Comet ZTF

Cold weather and clear skies means it's time to see the comet!

Comet ZTF E3
On the morning of Thursday, Jan. 26, Comet ZTF (C/2022 E3) displays a bright coma and three separate tails. The long tail at upper left is made of gas that fluoresces in sunlight as it leaves the comet. The wider, overlapping tail is made of fine dust particles that reflect sunlight. To the right is an anti-tail, not an actual tail but an illusion from viewing the orbit of the comet edge-on.
Contributed / Eliot Herman

Maybe you've had a chance to look for Comet ZTF . In the Duluth, Minnesota region it's been cloudy for so many nights I almost despaired of seeing it before the waxing moon would wash it out. Finally, on Thursday, Jan. 26, my vigil paid off. I got up at 4 a.m., looked out the window and saw stars. Glorious stars!

Comet ZTF E3 and Little Dipper
Comet ZTF is just a little green dot (at the tick marks) in this photo taken with a 35mm lens at 5:30 a.m. Jan. 26. It appears just above the bucket of the Little Dipper. The comet will be crossing the northern sky between the Big and Little Dippers now through the end of the month.
Contributed / Bob King

Wary of clouds returning at any moment, I immediately tried to spot the comet without optical aid. It was conveniently positioned a few degrees above the Little Dipper's bowl at the time. Playing my gaze around the spot I soon found it — a soft, faint glow about half the size of the full moon. While hardly obvious, if you knew exactly where to look, there was no doubt even through barely awake eyes.

Next, I brought my 10x50 binoculars to the task. Right away, I could make out a big, fuzzy, wedge-shaped glow. Examining the comet carefully, the main tail (pointing west) stood out clearly. The other two tails — gas and anti-tail — took more sussing, but I saw both faintly with averted vision, a technique where you gaze around the object instead of staring at it directly.

Comet ZTF telephoto
You can faintly see the dust tail and overlapping gas tail to the left of the comet's head and the anti-tail to the right in this photo taken with a 200mm lens on a tracking mount at 5 a.m. on Jan. 26.
Contributed / Bob King

I eagerly set up the telescope while the wind bore down from the spring stars overhead. Yes, spring. When you wake up to stargaze in the morning hours you get to "cheat the season." The Earth rotates while you're asleep. Go to bed at 10, and the winter constellations of Orion, Gemini and Taurus still dominate the sky. But 6 hours later, they've shoved off to the west to be replaced by the spring groups. I looked up to see Arcturus high in the southern sky, while the Summer Triangle and Milky Way rose in the east.

This remarkable time lapse video captures the comet losing its gas tail on Jan. 19 when a gust of solar wind snapped it off. Click the link to view.

Despite having looked at photographs showing Comet ZTF's green coloration, caused by carbon molecules fluorescing in sunlight, I wasn't prepared for the sight in the telescope. Wow! It was the first thing I noticed. We're not talking golf course green but something much more subtle. Imagine seeing a green traffic light from a distance through heavy fog.


Comet ZTF E3 Jan 25_27 Eliot Herman S.jpg
You can see how Comet ZTF changes over time due to activity, distance from the sun and viewing perspective. This panel covers three nights.
Contributed / Eliot Herman

Through the telescope the comet was so big it was hard to make sense of its hazy appendages at first. But by moving the scope this way and that I was better able to distinguish one tail from another. Off to one side of the comet's head a bright spot of light called the false nucleus got my attention. It looked just like a fuzzy star. Photographs often overexpose this feature; it really stands out in person.

This woolly nugget is where all the action begins. Within the false nucleus is the actual comet nucleus, an icy object several kilometers across that partially vaporizes when heated by the sun.

Comet ZTF anti-tail
On Jan. 23, the Earth passed through the comet's orbital plane. For a few nights around the time, as we looked up to see it, dust shed by the comet in the plane of its orbit stacked up along our line of sight to create glowing, stubby anti-tail (tail sticking out to the left or lower left in all the photos). It's called "anti" because it points opposite the genuine tail. The anti-tail will soon disappear as the Earth leaves the comet behind. The dust stream lies in the distance well away from Earth. Had we passed directly through the comet's dust we would have seen meteors.
Contributed / JPL HORIZONS

Embedded in the ice are organic molecules, dust and frozen gases such as water, methane and ammonia. When released they create a temporary, fuzzy atmosphere around the nucleus called the head or coma. Tails form when sunlight either fluoresces (in the case of gas) or physically sweeps dust particles back behind the coma.

Lovejoy coma
This is a sketch I made of the coma and false nucleus of Comet Lovejoy that appeared in January 2015. Comet ZTF's coma and nucleus appeared similar.
Contributed / Bob King

Comet ZTF's false nucleus was very obvious. I used high magnification to see if any dust jets were visible, but being low contrast features I wasn't sure of seeing them. Jets form when ice inside the comet turns to vapor and blasts out through a crack or hole in the surface. They look like small geysers close to the nucleus.

After photographing the comet I took a few minutes to look around and enjoy the early summer sky. I also dropped in on several seasonal treasures — the Ring Nebula, Hercules Cluster and one of my favorite double stars, Acrab (Beta Scorpii), in the head of the Scorpion. With the wind determined as ever and the temperature at 2 below, it was a joy to return to a warm house.

The very next night was clear again. This time a whole group of us looked at the comet from a snowy road overlooking Duluth's Lakeside neighborhood. Despite moonlight and light pollution everyone loved seeing the comet. Most described it as a smudge, but there were no complaints. Sometimes you don't need a lot of fanfare and rah-rah. The simple "is-ness" of nature is enough.

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at
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