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The mass media is headlining a rare “green comet” passing by Earth between February 1 and 2. It’s supposedly about to be visible to the naked eye and be the best comet of 2023. Well, that last part may prove true, but as for the rest, pull up a chair.
Do you first want the good news, or the bad? Well, let’s get the bad stuff out of the way.
What is the Comet’s Name
The comet’s name is “C/2022 E3 (Z.T.F.)” because was found last year (2022) on Palomar Mountain in California by a special super-wide field telescope named the Zwicky Transient Facility (or Z.T.F.). It seems to orbit the Sun and come reasonably close to the Sun and Earth only every 50,000 years!
On January 12, Comet ZTF reached that nearest-to-Sun point (its perihelion) which is when comets usually have their ices turn maximally to vapor, creating the comet’s signature feature, its tail. That’s also when the Sun’s ultraviolet light most intensely acts on the carbon in their 10-to-20 mile-wide nucleus to ionize that element, whose already-rare carbon-to-carbon bond then emits green light. A huge fuzzy glow called a coma surrounds the comet’s head, and this often has a wonderful green glow.
Except you’ll never see that green glow. Our vision is colorblind at low light levels, and Comet ZTF is faint even through telescopes. So actually, the bad news only begins at this point. Because, this comet is faint. It MIGHT reach naked-eye visibility, but only for those who live far away from cities, and even then it’ll be very, very dim.
Oh, and did we mention that comet ZTF shows no tail? Not to human eyes, not even through binoculars. So those great green photos you may have seen, those features and colors only appear using long-exposure astrophotography. A tail may eventually appear photographically too, but for visual observers hunting pathetically for this interloper in our inner solar system, it’ll be a dim, colorless, tailless blob.
But still worth hunting for? That’s up to you. Me, I’m a comet lover who has seen two dozen all told, but a tailless comet belongs in a special class that may include furless cats and my sister’s culinary specialty, tuna casserole with marshmallows.
But I’ll hunt for it anyway. If you succeeded in finding the last naked eye comet, Comet Neowise in 2020, know that this one is fainter. You’ll need dark rural skies.
When is the Comet Most Visible?
Comet ZTF is already nearly visible to the naked eye as it swings toward the Earth. As it comes closest to Earth on February 1 and 2, Groundhog Day, the comet will be steadily brightening. From the Northern Hemisphere, the comet is likely to be faintly visible to the naked eye.
Where to Look for the Green Comet
You can start the next clear night by sweeping binoculars around Polaris, the North Star. Actually, not very close to Polaris, but below it between nightfall and 11 PM, and above it during the four hours before dawn. If you know how to locate the North Star by following the two stars on the end of the Big Dipper’s cup, then you should be able to spot the comet as a faint smudge between the Big Dipper’s “cup” and the North Star. A modest set of binoculars will help.
But the comet-spoiling Moon will be waxing or brightening between now and then too. So here’s the best compromise, since dark skies and an absent Moon are more important than the comet coming closer:
Try early in the morning after the Moon has set. Between now and February 2, the Moon sets at least a few hours before dawn, which is just when the comet will be highest up in the north, above Polaris.
So set the alarm and go out at least 1 ½ hours before your local sunrise to look for the comet, using binoculars.
By February 1, it might even be faintly visible to the naked eye. But no tail, no color. You’re looking for a round, faint, ball of fuzz. And if you’re in a city, forget the whole thing!
Will you join the hunt? If you do, continue why comets are so special. Besides being something rare to see, comets come from an ancient solar system and help us understand how Earth began.