How to observe the ‘green comet’ in the night sky

A green-hued comet from the outer solar system is expected to cross Earth’s neighborhood in the coming days for the first time in 50,000 years.

The comet is steadily gaining brightness and will make its closest approach on February 2, when it will be within 26.4 million kilometers of the planet, or 110 times the distance to the moon. From the northern hemisphere, the comet is likely to be faintly visible to the naked eye.

But you don’t have to wait until February to spot this rare visitor. The coming weekend can provide favorable viewing opportunities with a pair of binoculars when the new moon creates darker skies.

Q: What is the name of the comet?

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

At the time, the cosmic intruder was just inside Jupiter’s orbit and about 25,000 times fainter than 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 every night and is well suited to discover such objects.

Q: What are comets and why is this one green?

A: Comets are frozen clumps of dust and gas, sometimes described by astronomers as “dirty snowballs.” Most are thought to come from distant, icy regions of the solar system where gravitational agitations sometimes push them towards the sun – an interaction that transforms them into magnificent cosmic objects.

When they leave their freezing, the heat of the sun erodes their surfaces and they begin to spit gas and dust until they harbor a glowing core, known as a coma, and a tail shaped like a flame that can span millions of miles.

“They’re alive,” said Laurence O’Rourke, an astronomer at the European Space Agency. “When they are away from the sun, they sleep, and when they get closer to the sun, they wake up.”

C/2022 E3 (ZTF), for example, now glows green because the sun’s ultraviolet radiation 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?

A: The brightness of comets can be unpredictable. When scientists first discovered the object last year, they only knew it had the potential to be visible from Earth.

“Because each comet is its own living thing, you don’t know how it’s going to react until it passes in front of the sun,” O’Rourke said.

Comet C/2022 E3 (ZTF) made its closest approach to the sun on January 12, and the comet is now brightening steadily as it heads toward Earth. Although the comet won’t pass us until Feb. 2, it’s already nearly visible to the naked eye — an encouraging sign for observing opportunities, said University of Maryland astronomer and co-lead Mike Kelley. of the Solar System Task Force at the Zwicky Transient Facility.

Still, seeing the comet might “require dark skies and an experienced observer,” Kelley said.

Moreover, comets can always surprise us. Sometimes there may be a big explosion of gas and dust, and the comet may suddenly become brighter even after leaving the sun.

Q: How to spot the green comet?

A: To catch the comet, look north.

On January 21, the night of the new moon and therefore darkest sky, the comet was close to Draco – the dragon-shaped constellation that stretches between Ursa Major and Ursa Minor.

During the following nights, the comet will glide along the tail of the dragon. And on January 30, the comet will reside directly between the “cup” of the Big Dipper and Polaris, the North Star. If you are used to finding the North Star by following the two stars at the end of the Big Dipper cup, you should be able to spot the comet. Simply sweep over this imaginary line until you see a faint smudge.

If you’re struggling, the comet may still be too faint or there may be too much light pollution. Try with a pair of binoculars.

“Even with relatively modest binoculars, the powdery, fuzzy, or smoky character of the ‘star’ should clearly indicate that it is a comet,” said EC Krupp, director of the Griffith Observatory in Los Angeles. .

A telescope will help you spot the finer colors and details, including the comet’s bright coma and long tail.

For anyone living above the 35th parallel — imagine a curved east-west line running from North Carolina across the Texas Panhandle to southern California — the comet is visible all night beginning January 22. But it’s relatively low on the horizon in the early evening, and it might be best to look for the comet later in the evening or even early in the morning when the comet is swinging higher in the sky.

Krupp recommends watching when the phase of the moon is new and therefore won’t cast a glow in the sky. But the comet will get brighter as it gets closer to Earth and will be easier to spot towards the end of the month. If you wait until then, you might want to try early in the morning after the moon has set.

In any case, the hunt will be fun.

“It’s kind of like looking for endangered species and then it pops up,” Krupp said. “He really is an experienced charmer.”

Q: Why are astronomers excited about this green comet?

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

“It’s really a situation where we probably wouldn’t exist without them,” O’Rourke said.

And yet, we don’t get many opportunities to study these objects, since only a few each year are bright enough to see with the naked eye. So comet astronomers around the world will be observing C/2022 E3 (ZTF) over the next few 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 in late February. He wants to better understand how our planet was formed in order to note the conditions that gave rise to life on Earth.

But Kelley and others need to work fast. After a brief appearance in the night sky, it is unclear where C/2022 E3 (ZTF) may go. Because these objects are so loosely tied to our solar system, the sun’s gravitational influence could force the comet to make another trip around our star – perhaps not return for 50,000 years. Or the sun could completely drive the comet out of the solar system.

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