The headlines at the start of the year spoke of a “green comet” or “Neanderthal comet” that last sailed by the Earth 50,000 years ago and was gazed at by awed cave dwellers. In truth, we don’t know the exact timing of that ancient fly-by and if any Paleolithic people noted it.
What we do know is that C/2022 E3 (ZTF) is a long-period or non-periodic (“C/”) comet first sighted last year (“2022”) in early March (“E”) as the 3rd (“3”) comet discovered in the first half of that month. The facility that found the object was the Zwicky Transient Facility (“ZTF”). The green glow is not uncommon in comets: it is due to the presence of diatomic carbon and cyanogen shed by the comet and fluorescing from solar radiation.
The closest approach to Earth (0.28 astronomical units) was the evening of February 1st Universal Time when it was high in the northern sky near the pole as a magnitude 4.5 fuzzy object. Visually, with the Moon 84% full, the comet was washed out with just the triangular-shaped coma visible and no sweeping tail like in the long-exposure photographs.
If you’ve been studying images of the comet you’ll note how cometary features, on images a few days apart, can show dramatic change. This included an ion tail “disconnection” event and an antitail as it neared Earth — caused by particles shed by the comet becoming visible as the plane of Earth’s orbit intersected the plane of the comet’s orbit.
Taking full advantage of the wide field afforded by the Tele Vue-76 APO (mobile site) refractor, Brian was able to capture much of the incredibly long ion tail of the comet using a QHY 268M astro camera. The green ionization around the comet is very prominent and the dust tail is short and trails behind the coma.
On January 21st Brian captured an ion tail disconnection event (the thin vertical tail) using the same Tele Vue-76 APO setup as the color image above. To create the video below, 23 Luminance frames of 2-minute exposure through a luminance filter were star-aligned using PixInsight. The images were then exported into Photoshop where the video was created. Numerous satellite trails had to be removed in order to get the final “clean” video presented here.
From northern California, Michael used our Tele Vue-NP101is APO refractor (mobile site) and a full-frame DSLR camera to capture the long tail of the comet that overlapped the blue ion tail, the green glow around the coma, and the stubby antitail appearing to the right of the coma. To gather all this detail required an hour-long exposure taken one minute at a time.
The comet made a nice pass by Mars in the second week after the closest approach to Earth.
A Tail of 3 Comet Tails
We often marvel at a comet’s “tail”, but in this blog we talk about the comet having three tails. What are these tails? They have to do with the composition of the comet and the environment it is passing through. Fred Whipple’s popular model of a comet as a “dirty snowball” speaks to the typical comet’s composition of rock, dust, and volatile compounds such as water ice, frozen carbon oxides, ammonia, and some hydrocarbons.
The dust tail arises when the frozen volatiles are evaporated by the Sun: solar radiation pushes the liberated dust grains away from the Sun. The sunlight-reflecting stream of dust appears as a long tail that can be millions of kilometers in length and sometimes quite broad. We know the Sun is causing this because the comet, whether approaching or receding from Sun, always has a dust tail pointing away from the Sun. On long tails, the momentum of the dust in the direction of orbit causes the tails to curve.
High energy ultra-violet rays from the Sun knock electrons off the gasses to create positive ions. These ions follow the path of the charged particles from the solar wind to form the ion tail that always points away from the Sun. Since ionized carbon molecules emit blue light, this is the prominent color of the tail. Changes in the solar wind can cause disconnection events in the ion tail where a section of that tail is pinched off and ripped away from the comet.
Large particles left behind by the comet are less impacted by solar radiation and remain in the orbit of the comet. If the line of sight between Earth and the comet’s orbital plane lines up, and there is a sufficient density of particles, this edge-on view reveals a spike extending in front and behind the comet’s path of motion. Usually, only the antitail spike, opposite the dust tail, is prominent as the other is obscured by the dust tail. Meteor showers happen when the Earth passes through these discarded particles that continue to orbit the Sun as the comet does. Earth crossed the orbital plane of comet ZTF on January 22/23, so you’ll see a prominent antitail in comet images taken on those days. A few days on either side of this time period the antitail will look shortened and at an angle to the ion tail.
Chris used a Tele Vue-NP101 APO with NPR-1073 0.8x reducer (f/4.3) to create a fast imaging system for his hydrogen-alpha sensitive Canon 60Da camera. This image, taken a few days before the closest approach, shows a compact coma, a faint ion tail, and a dust tail. The Tele Vue-NP101 scope has been replaced by the Tele Vue-NP101is APO refractor (mobile site) in our product line.
Mike used a Tele Vue-85 APO (mobile site) with TRF-2008 0.8x Reducer/Flattener to create an f/5.6, 480mm, lens for his QHY294C-Pro color camera to image the comet a few days after the closest approach. Note the long ion tail going out of the frame. This was also the “first light image” for the camera. Mike told us about the conditions:
The bright moon was near the comet and made getting the dim ion tail very hard. Luckily, I was able to fix most of that issue with a good “flat” calibration frame. There were still minor issues with the right side part of the frame on one set of sub-images where the tail is and I actually had to dim it down a bit.
Alexander’s image of Comet ZTF was made with the Tele Vue-NP101is APO refractor (mobile site) and a total exposure time of just over an hour with a ZWO ASI2600MC Pro color camera. This is a well-balanced image showing a prominent antitail extending from the green fluorescence around the coma. The lengthy ion tail is aligned with the dust tail against a star-studded, uniform, dark background.
We hope you enjoyed the images as this is the last we’ll see of this comet: this passage through the Solar System has perturbed the orbit enough to cast it out of the system or at least on a return orbit that will take millions of years.
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Images of Comets Past