C/2022 E3 (ZTF), also known as Comet ZTF for short after the Zwicky Transient Facility discovered it in March, hasn't been in our cosmic neighbourhood since the last Ice Age.
Researchers calculated that the icy ball of gas, dust, and rock orbits the sun roughly every 50,000 years, which means that Neanderthals were still walking the Earth and humans had just migrated out of Africa for the first time when the comet last whizzed by.
Those ancient peoples may not have seen the comet at all because they did not have telescopes or binoculars. And there may never be another chance to see it.
"Some predictions suggest that the orbit of this comet is so eccentric it's no longer in an orbit — so it's not going to return at all and will just keep going," Jessica Lee, an astronomer at Royal Observatory Greenwich, told Newsweek.
According to NASA, the green comet should be visible in the Northern Hemisphere just before dawn in late January.
In the Northern Hemisphere, the green comet should be visible just before dawn in late January, according to NASA. A completely shaded new moon could provide ideal dark skies for spying the comet on January 21. Then in early February, the comet will be visible in the Southern Hemisphere.
On February 2, comet ZTF will pass about 26 million miles from Earth, its closest approach. That's nearly 109 times the average distance between the Earth and the Moon, but the comet is so bright that it may still be visible in the night sky.
According to the Adler Planetarium, the comet will be the "faintest an object that can be seen without optical aid in a very clear, very dark sky" on January 31 and February 1.
If you're looking for it, you should prepare yourself for success.
How to spot the green comet
At first, spotting Comet ZTF may require a telescope, but as it approaches Earth, viewers may be able to see it with binoculars, or even the naked eye.
"Comets are notoriously unpredictable, but if this one continues its current trend in brightness, it'll be easy to spot with binoculars, and it's just possible it could become visible to the unaided eye under dark skies," NASA wrote in an update on December 29.
For the best viewing, choose a cloudless night and get yourself far from city lights, to the darkest skies possible. When the moon is dim, or at least when it's below the horizon, the sky will be even darker.
If you're near an urban area, you may want to bring binoculars or even a telescope, in case the lights drown out the comet to the naked eye.
Where to look in the night sky for comet ZTF
Look to the right stars to see the green comet. According to EarthSky.org, the comet is currently visible passing through the Botes constellation, near its border with Hercules. It's headed toward Polaris — the North Star — and will be visible in the star's vicinity on January 30. It will appear earlier in the evening as it approaches Polaris.
"It will distinguish itself probably from other stars because it will look a little bit fuzzy compared to other stars," Thomas Prince, director of the WM Keck Institute for Space Studies at Caltech, told FOX Weather.
In the Southern Hemisphere, on February 10, the comet will be about 1.5 degrees from Mars, according to Prince. That's about the width of your pinky finger when you hold it at arms length. If you can locate Mars shining bright in the sky, look just around it for the comet.
EarthSky publishes maps to help you locate the reference objects — Hercules, Polaris, and Mars — in the night sky.
Why the comet is green
The comet has a "greenish coma, short broad dust tail, and long faint ion tail," according to NASA.
Many comets glow green. Laboratory research has linked this aura to a reactive molecule called dicarbon, which emits green light as sunlight decays it.
Dicarbon is common in comets, but it's not usually found in their tails.
That's why the coma — the haze surrounding the ball of frozen gas, dust, and rock at the center of a comet — is glowing green, while the tail remains white.
Source: Business Insider