Green comet streaking across the sky

There’s been quite a bit of news about this brightening comet with pretty exciting hype but there are quite a few things to unpack here.

The comet being referred to has the technical name C/2022 E3 (ZTF). 2022 means it was discovered in 2022, E3 means it was the 48th comet discovered that year. The first comet that was discovered each year is A1, then you go up to A9, then B1 to B9, and so on until you run out of the alphabet, at which point you go to AA1, etc. ZTF is a discoverer of the comet. Gone are the days when people actually discovered comnets, though it does still happen sometimes. Some of the romance has been lost, and people often recall magnificent comets like Halley, Hale-Bopp, Macholz, Hyakutake, all named after their discoverers (jointly in the case of Hale-Bopp). ZTF here, though, is the Zwicky Transient Facility - a survey telescope at Mount Palomar looking mainly for supernovae and gamma ray bursts, and does a sideline in new comets and asteroids. ZTF discovered this comet in March 2022, and it has taken nine months for it to reach the Sun and make its cloie approach to us, here on the Earth.

A comet being ‘green’ is not so unusual. Most ‘new’ comets (comets that have not been round the Sun before, or extremely long period), tend to show green which is caused by a complex reaction involving diatomic Carbon (a molecule of two carbon atoms, C2). However the green is concentrated around the head of the comet, and is often overwhelmed by the light of reflected sunlight from the gas and dust that has been driven off as it heats up approaching the Sun. Many current photos from expert astro-imagers show a small amount of green. Those that don’t take too much care with their color balance might show it with a greater overall green tinge. Practically if you go out to look at the comet with the unaided eye or binoculars it is unlikely to look very green - both because there is not that much green, and it the comet will not be so bright that our eyes will register the green.

As far as ‘streaking across the sky’ is concerned. Well, depends on your definition of streaking. But it’s not like a meteor or fireball. It is making fairly sedentary progress across the sky - though compared to most astronomical objects, it is moving very quickly. This makes it a little tricky to find, and at the moment, a good chart and an understanding of what star is which is pretty necessary to see it with binoculars. If you do manage to find it one evening and then look later in the night, say an hour later, you will notice it has moved quite a distance on the sky. As the comet gets closer to earth, and closest approach is Jan 31 or Feb 1, it is expected to be brighter, but just at the limit of detection to the unaided eye. Possible if you are looking from a dark-sky location and have become prosperity adjust to the darkness.

Here is a chart showing the location of the come over the next few weeks.

I have not had great weather for trying to take pictures of ZTF but I managed to get a wide-field image of this comet on January 7th, but it was just a faint blob on the picture.

Another session on the evening of January 20th with a different telescope showed the comet better, but in all fairness it is still just a blob! Though there is a hint of the tail. Hopefully in the coming couple of weeks I will get some better weather to get a more satisfying picture.

Some final thoughts.

Don’t be put off - it’s not really going to be a splendid comet like C/2020 F3 NEOWISE which put on a great show a couple of years ago - but it’s not very often that we have a comet which is visible to the unaided eye. Get a good chart - there are plenty on the internet - or use an app or planetarium software like Stellarium so you can see exactly where the comet will be when you go out to look at it. And it is going to be well placed for everyone in the northern hemisphere - available all night long. Try a pair of binoculars first. Simple common or garden 10x50s like you might use for bird-watching are fine And try to locate the comet by hopping from a nearby star to where the comet should be. Good luck!

And if you do manage to find and see this comet - let me know.