How to watch the 'green comet' while you still can

A green-hued comet from the outer solar system is swinging through Earth's neighborhood for the first time in 50,000 years.

The comet has been steadily gaining brightness and will make its closest approach Thursday, when it comes within 26.4 million miles of the planet. That's 110 times the distance to the moon.

From the Northern Hemisphere, the cosmic visitor will be faintly visible to the naked eye — so faint that you will want to grab your favorite pair of binoculars and drive far from city lights. And be forewarned that it will look nothing like many of the images you've seen on the internet. But it is your best chance this year to view an object from the solar system's distant, icy reaches.

"I get this tingly, magical feeling whenever I'm looking at something live through a telescope," said Andrew McCarthy, an astrophotographer based in Florence, Arizona. "You just can't beat what your eyes can see."

Q: What is the comet's name?

A: The comet is known as C/2022 E3 (ZTF) because astronomers discovered it in March 2022 using a telescope on Palomar Mountain in California called the Zwicky Transient Facility (or ZTF).

At the time, the cosmic interloper was just inside the orbit of Jupiter and roughly one-25,000th as bright as the faintest star visible to the naked eye. But ZTF, with a camera that has a wide field of view, scans the entire visible sky each night and is well-suited to discover such objects.

A: Comets are clumps of dust and frozen gases, sometimes described by astronomers as dirty snowballs. Most are believed to originate from the distant, icy reaches of the solar system, where gravitational agitations sometimes push them toward the sun — an interaction that transforms them into gorgeous cosmic objects.

When they leave their deep freeze, the sun's heat erodes their surfaces. They start spewing gases and dust until they host a glowing core, called a coma, and a flamelike tail that can stretch for millions of miles.

"Their activity makes it look like they're alive," said Laurence O'Rourke, an astronomer with the European Space Agency. "When they're far from the sun, they're sleeping, and when they get close to the sun they wake up."

C/2022 E3 (ZTF), for example, is now glowing green because ultraviolet radiation from the sun is absorbed by a molecule in the comet called diatomic carbon — that is, two carbon atoms fused together. The reaction emits green light.

Q: How bright will this comet be?

"Because each comet is its own living being, you don't know how it's going to react until it passes the sun," O'Rourke said.

Comet C/2022 E3 (ZTF) made its closest approach to the sun Jan. 12 and is now steadily brightening as it swings toward the Earth. While the comet won't pass us until Thursday, it is already visible to the naked eye — an encouraging sign for viewing opportunities, said Mike Kelley, an astronomer at the University of Maryland and a co-leader of the solar system working group at the Zwicky Transient Facility.

Still, many agree that dark skies and a pair of binoculars are a must.

Q: How do I spot the green comet?

A: To catch the comet, look north.

But Monday, Comet C/2022 E3 (ZTF) resided directly between the two stars at the end of the Big Dipper's cup and Polaris, the North Star. Through Thursday, it is creeping along an imaginary line roughly parallel to the back of Ursa Major, also known as the Great Bear.

That recognizable location will give a lot of viewers the chance to scour the skies for the comet. And the hunt will be fun.

"It's sort of like searching for some endangered species, and then it pops into view," said E.C. Krupp, director at Griffith Observatory in Los Angeles. "That really is a charmer of an experience."

Q: What's the best location and time to see it?

A: There is one major adversary in this hunt: light.

Then, even if you manage to escape the city lights, you will have to contend with moonlight. The next full moon will be Sunday — only days after the comet's closest approach. That means it might be best to view the comet as soon as possible, when you can spot it after the moon has set and just before the sunrise.

Q: What equipment do I need?

A: Although this comet is technically visible to the unaided eye, it is quite likely that you will need a pair of binoculars.

"Even with relatively modest binoculars, the powdery, fuzzy or smoky character of the 'star' ought to make it clear it's a comet," Krupp said. And, their wide field of view helps you scan large areas of the sky at once.

Even if you don't have a pair of binoculars, the investment might be worth it. "Space is so accessible," McCarthy said. "You can see the whole sky — like nebulas and galaxies — with binoculars, and it looks incredible."

A: The comet, even through a pair of binoculars or a telescope, is going to be a far cry from many images shared on the internet. The human eye isn't sensitive enough to pick up the green color in such low light.

"Most astronomical objects appear black and white, even with the aid of a telescope," said Alan Dyer, an amateur astronomer based in southern Alberta. "It's only the camera, the long exposure, that picks up the colors."

Q: How do I photograph the green comet?

A: McCarthy took a picture of Comet C/2022 E3 (ZTF) on Jan. 18 in which the coma is the color of a green apple and the ion tail fans outward like rays of purple sunshine. He used his telescope to shoot 45 60-second photos and then spent 18 hours compiling those photos into one final image. "A lot of processing wizardry goes into getting that final image," he said.

"But you don't need fancy equipment to photograph this," McCarthy said. If you use a tripod and a standard DSLR camera, "you'll be able to spot it, and you'll be able to resolve the green color and everything."

Q: It's cloudy. Is this my last chance?

A: No! In fact, given the brightness of the moon Thursday, it might be smart to wait awhile longer. At that point the darker evening hours before the moonrise will be a prime time to look for it. It's true that the comet will be fading at that point, but it most likely won't fade too fast — meaning it will still be an easy catch with a pair of binoculars.

"It's going to be with us in the sky for a while," Dyer said.

Comet C/2022 E3 (ZTF) will pass by the bright star Capella on Sunday night and then swing by Mars on Feb. 10. Those bright objects might even make it easier to find, Dyer argued.

So make sure to try again if your skies are cloudy, but don't wait too long. Comet C/2022 E3 (ZTF) is expected to be the brightest comet visible this year.

A: Comets are relics of the early solar system, and they may have been responsible for seeding early Earth with the building blocks for life.

"It really is a situation where we most likely would not exist without their existence," O'Rourke said.

And yet we don't have many opportunities to study these objects, given that each year only a few are bright enough to be seen with the naked eye. As such, cometary astronomers across the globe will observe C/2022 E3 (ZTF) over the coming months.

"We're looking for our solar system's place in the universe," said Kelley, who will use the James Webb Space Telescope to observe the comet at the end of February. He wants to better understand how our planet formed in order to note the conditions that gave rise to life on Earth.