How to see the naked-eye comet C/2022 E3 (ZTF)

Subscribers shine brightly as they fall toward the Sun

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Look up! There’s stuff to see in the sky!

There’s a comet brightening in the sky right now and it may be a worthwhile object to take a look for the next couple of weeks. Called C/2022 E3 (ZTF) —let’s call it E3 for short — it’s been falling toward the inner solar system for thousands of years, and when it heads back out it may not be coming back for a long time, if ever.

Now I want to be VERY careful here and stress that while this is technically a naked-eye object, as of this writing it’s only barely so and not likely to get hugely brighter. You’ll really want binoculars or a telescope to see it. The view probably won’t be spectacular, certainly not like in photos taken of it, but instead will show a small fuzzy dot with a fuzzy tail sweeping away from it.

That’s true of a lot of things at the eyepiece. But the fun is in knowing what you’re seeing.

The comet was discovered in images taken by the Zwicky Transient Facility — hence the ZTF in the name — in March 2022, when it was roughly 600 million kilometers from the Sun, almost as far as Jupiter. The orbit is very nearly parabolic, which means it’s been falling in from a long way out, certainly from the Oort Cloud of icy objects out past Neptune. Its orbit is tens of thousands of years long, and slight changes in its orbit means it’ll either be ejected from the Sun after this pass forever or take millions of years to return. Either way, this is your only chance to see it.

It’s already reached perihelion, its closest approach to the Sun, which was on January 12. It reaches perigee, when it’s closest to Earth, on February 1, when it will be roughly 40 million kilometers from us. Unless something happens and it brightens a lot, it won’t be visible by eye unless you go to a dark site, and even then I’ll only be visible without optical aid for a day or two before and after perigee.

The good news is its location in the sky: Toward the end of January it will be far to the north, close to the Big and Little Dippers, which means it’s up pretty much all night and decently high off the ground for most northern hemisphere observers. In fact, you may know the old method of finding Polaris, the North Star, by using the “pointer stars” at the end of the Big Dipper’s bowl, which point very nearly toward it.

Well, on January 29 E3 will also be on that line, so you can follow those stars to find it as well!

Objects near the north celestial pole are said to be circumpolar, and while they make a circle around the pole once per day they don’t dip below the horizon (depending on your latitude). From January 28 – 30 E3 will be within about 10° of Polaris, so it’ll be circumpolar, making it easier to find. Since it does move relative to the stars night after night your best bet is to use planetarium software to get its position. I use Sky Safari on my phone/tablet but Stellarium is also pretty easy to use. Just search on “C/2022 E3 (ZTF)” and it’ll show up. You can change the date and time, too, so find out when it’s up where you are and go hunting.

I’ll note the waxing Moon will be an annoying interference later in the month, washing the sky with light and making it harder to see faint fuzzies. So I’d err on the side of looking earlier than perigee if possible. By January 25th or so it’s high enough off the northern horizon to spot easily at, say, 9:00 p.m. local time, though it’s best around midnight.

In images the comet appears pretty green, which is common. Diatomic carbon — two carbon atoms bound together — is a molecule that emits light pretty vigorously in that part of the spectrum and is plentiful in comets. It might look green through an eyepiece, so that’s a fun thing to see.

You may also note that in a lot of the photos you see of the comet, there are two tails. One is the ion tail, and the other the dust tail. I explain them in the Crash Course video embedded above, but there’s also the matter of them pointing in different directions, sometimes even in opposite directions! When that happens the one pointing ahead is called thw anti-tail, and I explain that in an earlier issue fo this very newsletter.

Comet behavior is really difficult to predict. Most likely E3 will remain somewhat dim, though will look pretty cool with optical aid like a telescope. I remember in 2007 when Comet Holmes went from a faint ho-hum object to spectacular when it suddenly brightened by a factor of a million and became easily visible to the naked eye. It’s not clear why this happened; it may have impacted a small asteroid, or a gas pocket under its surface broke through. It was farther than the orbit of Mars when it happened but I could see it wasn’t a dot but an actual disk even by eye!

That’s an extraordinarily rare event, so don’t count on anything like that here. But comets do sometimes get brighter than expected, especially ones that drop in from the Oort Cloud — they can have lots of ice on them that warms up and turns to gas, which expands and reflects sunlight. E3 may yet surprise us. To be clear I don’t think it will, but that’s no reason not to go out and take a look.

Find out if any astronomy clubs in your area are doing any viewing; both Sky and Telescope and The Astronomy League have lists.

Comets getting even this bright are very rare, so I hope you have the opportunity to take a look if you can. I know I will be!

Et alia

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