What is a ‘green comet’ and where can you see it?
A green comet is flying past Earth for the first time in 50,000 years, offering skygazers a one-off opportunity to witness the celestial spectacle before it disappears from our Solar System forever.
The C/2022 E3 (ZTF) comet makes its closest approach to Earth on February 1, 2023. At a relatively close 42 million kilometers (26 million miles) from our planet, and with a brightness value of the magnitude of about +6, it will be possible to see it with the naked eye – weather permitting.
The comet is so rare that woolly mammoths and saber-toothed cats were still roaming the Earth when it was last swept by our planet.
Its perigee is on Tuesday and Wednesday, but it will remain visible throughout the week.
To find out where in the sky to look, and learn when conditions are best for viewing the comet, you can follow our live coverage in the blog below.
How to spot green comet if you missed it today
While the comet is expected to slowly fade away from the skies over this week, there may still be chances to get a glimpse of the cosmic entity over the following days.
The comet’s trajectory will take past the bright star Capella on February 5 after which it will swing by Mars on February 10.
The star as well as the Red Planet might make it easier to spot them on later dates but not for long.
With the ZTF comet expected to be the brightest one visible this year, experts say the darker evening hours before moonrise in the coming days could be the next best bet to spot it in the sky.
Graeme Massie2 February 2023 04:08
Green comet spotted over Greece
Graeme Massie2 February 2023 07:54
How bright was the green comet compared to others in history
The green comet ZTF is currently at its closest position relative to the Earth, zooming past the planet at about 57km/s at a distance of merely 26 million miles.
Its brightness has been estimated to be at a magnitude of about +6 – almost the threshold of what can be visible to the naked eye – and is also expected to be the brightest such space rock to zoom past Earth this year.
The brightness of objects in the sky is measured on a scale of apparent magnitude by astronomers.
The brighter an object, the greater its negative number and the dimmer it is, the greater will be the positive number.
For instance, the sun has -26 magnitude compared with the full moon whose magnitude is around -13 magnitude to the naked eye.
The brightest planet in the sky – Venus – is estimated to have a magnitude of about -3 to -4, and large comets that achieve a similar brightness are unofficially called great comets.
Comet Bennett, discovered by amateur astronomer John Caister Bennett in 1969, was a magnitude 8.5 object.
The 1986 visit by the famous Halley’s comet had a magnitude of about +2 while its next pass expected in July 2061 is estimated to likely have a fairly spectacular brightness of about –0.3.
The comet Bennett, discovered in 1969 by South African amateur astronomer John Caister Bennett, was a magnitude 8.5 object when it was first identified.
Some of the faintest stars visible to the unaided eye have magnitudes of about 6.5.
Vishwam Sankaran2 February 2023 07:25
Spectacular images shared of the ‘exotic’ green comet
If you’re yet to catch a glimpse of the green comet, we’ve got a round-up of images captured by professional and amateur astronomers in recent days.
One picture, from the New Scientist’s Abby Beall, was notable not for its spectacular nature but for its help in seeing the comet. As she noted, the comet might not actually be easily visible – but spotting it might be possible using a phone, as well as the helpful map that she assembled.
You can see all of the pictures here:
Graeme Massie2 February 2023 07:01
ICYMI: How green comet was first discovered
The green comet C/2022 E3 (ZTF) was found in March 2022 by astronomers from the Zwicky Transient Facility.
Researchers used ZTF’s robotic camera and software developed by staff scientist Frank Masci to detect a moving object.
It was initially thought to be an asteroid, but the space rock’s condensed coma and its trajectory indicated it was a comet.
“This particular object was spotted because of its motion in a sequence of images taken by ZTF,” said Tom Prince, professor of physics from the Keck Institute for Space Studies.
“At the time it was discovered, it was not known to be a comet. That came later after follow-up observations by many telescopes worldwide,” said Dr. Prince.
The comet has come closest to Earth today at about 41 million km (26 million miles) away, and after that, it is expected to disappear into the darkness of space, likely never to be seen by humans again.
Vishwam Sankaran2 February 2023 06:40
ICYMI: Green comet may never fly past Earth again
Scientists studying the green comet’s orbit trajectory say it is in an open “hyperbolic orbit,” meaning it may not return to the inner Solar System again.
Robert Massey, deputy executive director of the UK Royal Astronomical Society, told Newsweek that the comet’s orbit shape looks like a “very open curve.”
Astronomers, including Franck Marchis from the SETI Institute, also say the comet may “soon escape the Solar System entirely” due to its orbit.
“This is probably the last time this comet will ever be visible to us, or to anyone living on Earth….But maybe in a distant future, another intelligent species will see it coming close to their sun and their own home planet, ” Dr. Marchis tweeted.
“In that sense, this comet is carrying a piece of us – of all humanity – into the cosmos,” he said.
Vishwam Sankaran2 February 2023 06:18
Watch the green comet’s orbital path
The green comet is currently making its closest path to Earth in 50,000 years. This graphic, made using Nasa and JPL-Caltech data, shows the path of the green comet as it passes through the solar system.
You can find an excellent in-depth visual explainer on the comet right here.
Graeme Massie2 February 2023 06:05
ICYMI: What a comet’s green color reveals about its chemical composition
Based on the green color of the comet ZTF, astronomers say it contains molecules like diatomic carbon and cyanogen.
Diatomic carbon (C2) is a green, gaseous chemical with the formula C=C and is known to occur in the carbon vapor in comets.
While many comets glow green as they zoom past the Earth’s sky, it had for long remained a mystery why this hue never reached their tails.
Scientists as early as the 1930s had theorized that diatomic carbon that was created by the interaction of sunlight’s UV radiation and organic matter on the comet’s head was being further destroyed leading to the color.
But the theory hadn’t been tested until late 2021 as diatomic carbon is not stable.
Timothy Schmidt, a chemistry professor at the University of New South Wales, demonstrated in 2021 the mechanism by which the dicarbon molecule is broken up by sunlight.
“The green color comes from C2, which is itself a breakdown product of larger molecules in the snowball. The C2 breaks down into C atoms in a few days. The green is due to C2 absorbing and emitting light in a process known as fluorescence,” Dr. Schmidt explained in a tweet on Tuesday.
Vishwam Sankaran2 February 2023 05:52
What comet studies have revealed about the early Solar System
Studying the chemical composition of comets like ZTF have unraveled several secrets about the formation of the Solar System.
ZTF belongs to a category called long-period comets that are known to emerge from a shell of space debris in the outermost stretches of the Solar System called the Oort cloud.
The Oort cloud has not actually been seen by astronomers, but is theorized to be a vast, spherical shell made of icy debris, some of which may be as old as the Solar System itself.
A recent study, surveying gases like carbon monoxide and water vapor in 25 comets, suggested that analysis of these molecules from comets could trace the chemical composition of the early Solar System.
Scientists could unravel insights about early solar systems based on the ratio of certain molecules present after outgassing from comets.
The research found, for instance, that comets very far from the sun that have never, or only rarely, orbited near the sun, produced more CO2 than CO, whereas those that have made many several trips close to the sun do the opposite.
Vishwam Sankaran2 February 2023 05:16
Timelapse shows green comet passing over night sky
Seeing the green comet can be tricky, even when you know where to look and the weather is good.
Capturing it for a timelapse video, however, is almost impossible. It requires no light pollution, clear skies and a specialist setup like this one. But the results are spectacular:
Graeme Massie2 February 2023 05:03