The Comets ZTF, etc.

Among my sub-interests in the hobby of visual astronomy, the pursuit of comets is one of my favorites. I've been entranced by comets since seeing Halley's in 1985-86. Part of the allure is their fleeting appearance. I love to observe deep-sky objects such as galaxies and star clusters, but with few exceptions they are the same night after night. It's always possible to get a better view of a given object on a better night, or with a better telescope or better skills. But the comet that is observable tonight will have moved a bit (or a lot) by tomorrow, and over the course of a few nights is likely to show changes in brightness or morphology. Comets combine the elusive fuzziness of deep-sky objects with the variability of planets. So it's not surprising that my first two observing sessions of 2023 focused on comets.

On Thursday the 19th, I got a text that astronomy friends Greg and Bobby would be going to a local site in the evening. With work on Friday, I hadn't been planning on going out, but the sky conditions were promising and we're still in the part of the year when it gets dark before 7pm. So I joined them at Miller Island. There was actually a bit of haze in the air, so it wasn't as dark and transparent as on a really good night. Other than showpiece objects such as M42 and the Double Cluster, I tracked down the best comet in the evening sky, C/2020 V2 (ZTF)*. The comet was in Cassiopeia, and I found it easily enough in my 10" Dob. It was a classic fuzzball comet with a brighter condensation in the middle and the hint of a fan shape. 

Two other comets were technically above the horizon, but low and poorly placed above the lights from Klamath Falls and the mills just north of Miller Island. Those would be targets for a morning session. 

I planned to go somewhere on Saturday morning. With frigid winter conditions (15 degrees Fahrenheit), I opted for Miller Island again instead of a farther and darker site. The wildlife area opens at 4am. It took longer than expected to free my windshield from the glaze of ice, so I didn't get out there until nearly 4:30. Again, there was a bit of haze that made the sky more gray than black. I have a SQM-L sky quality meter, and the readings hovered around 20.6. Good nights at Miller Island are typically 20.8-20.9. I probably could have gained 0.5 magnitudes by driving an additional half hour, but decided to save the mileage for another day. Limiting magnitude (the faintest stars I could see) was 5.9.

With the formalities out of the way, I went after the comets. The first one was C/2022 E3 (ZTF). If you've seen news about a comet recently, it's probably about this one. Generally the hooks in the headlines are either "green comet" or "first time in 50,000 years". By the way, many comets will show a green or cyan color, especially in time exposure images. And many comets have long-period orbits or are even making their first trip ever to the inner solar system. But, that's the nature of the news cycle. I'd even seen this comet before; it was on its way in and visible in the evening sky in late September, and while faint it showed a tail in my 10" scope even then. Now it has brightened to the edge of naked-eye visibility. It was really on the edge at Miller Island. I only got an occasional glimpse. But the comet was a fine object in my 8x42 binoculars. It looked bright and condensed. The coma was about 14' in diameter. Fortunately, the comet was in the darkest part of the sky, so I was also able to make out its double tail structure. A fan-shaped dust tail was visible in PA 320 (NW) and about 1.5 degrees in length. A thinner, fainter gas tail extended for over 2.5 degrees in PA 280 (WNW). I estimated the comet's magnitude as 5.8.

The comet was also a nice target for my 10" Dob. The coma showed a bright stellar pseudonucleus that may have had just a tinge of cyan color. Otherwise, the coma was fan-shaped and colorless but showed some interesting jet and streamer structure. The main dust tail was a broad fan in PA 320-350 and then fading out a bit but extending to a distinct southern edge at PA 40. The gas tail was fainter and thinner and in PA 305. The discrepancies in the tail directions between the binoculars and scope come from me "eyeballing" the position angles in binoculars and from taking them off of my sketch in the telescope. Over the 45 minutes that I spent on the sketch, the comet moved slightly. More detail but less tail length was visible in the telescope; the tails faded out after 0.3-0.5 degrees. The comet isn't some outstanding example, and it's only once-in-a-lifetime in the literal sense. This comet won't be back after it recedes in its orbit, but there will be others that look a lot like it and hopefully some that are significantly better (e.g., C/2020 F3 (NEOWISE) in 2020). But if I were a new astronomer with binoculars and a small telescope I would be excited to see it. And I'm an older astronomer with binoculars and a medium-sized telescope, and I'm still making the effort to see it.

Just before twilight encroached and fog moved in, I found my other cometary target, C/2022 A2 (PanSTARRS). It was another fuzzball comet, with even less structure than C/2020 V2. It was round or slightly oval with only a faint central condensation, but the best part about it was the star field. The comet was sitting near a pretty asterism (star grouping) and I find this sort of pairing between the sharpness and patterning of the stars and the soft light of the comet to be aesthetically pleasing. The two brightest stars in the asterism were yellow and reddish, so that was neat as well.

I packed up and headed out into the hazy, brightening dawn. I'll likely try to get some more views of C/2022 E2 (ZTF) over the next couple of weeks if the weather cooperates. After all, it is a once-in-a-lifetime comet, and maybe it will show more green in a darker sky …

* Both C/2020 V2 (ZTF) and C/2022 E3 (ZTF) were discovered by the Zwicky Transient Facility. C/2022 A2 was discovered by the Pan-STARRS survey.