Green comet: is comet C/2022 E3 visible from Earth in 2023, how to see it in the UK tonight - what is a comet?

A ‘green comet’ that hasn’t been witnessed from Earth in tens of thousands of years has reemerged in the night sky, capturing the attention and imaginations of stargazers across the world.

Many comets exhibit orbits around our sun of such a large scale that they can take decades to reach back around to our planet’s skies. Comets like the famous Halley’s Comet are only visible from Earth once every 75 years or so for instance, making them once in a lifetime spectacles.

But comet C/2022 E3 (ZTF) goes quite a bit further. Roughly 45,000 years further in fact, and it hasn’t been observed by viewers on our planet since the time of the Neanderthals.

So how can you spot this comet - which won’t be seen again for another 50,000 years or so - for yourself? Here is everything you need to know about it.

Why is the comet ‘green’?

Comets are ancient balls of ice and dust that orbit the Sun on extremely elliptical orbits. They warm up as they get closer to the sun, converting their surface ice into gas, which disperses and displaces dust in the process.

It is this process that gives comets their distinctive dusty “tails”, which can appear to stretch out behind them (in reality, comet’s tails point away from the Sun) for millions of miles as they travel through the Solar System.

Images of comet C/2022 E3 have already been captured by astronomers, and show a faint green glow that is thought to be caused by the presence of diatomic carbon, bonded pairs of carbon atoms which emit green light when stimulated by the Sun’s ultraviolet energy.

The comet originates from the Oort cloud at the fringe of the solar system, a spherical layer of icy objects that is thought to be located between 2,000 and 100,000 astronomical units (AU) from our Sun.

To give you an indication of how far away that is, one AU is measured as the average distance between the Earth and the Sun - about 93 million miles.

When is the best time to see it?

The comet will make its closest pass of Earth at a distance of 27 million miles, on Wednesday and Thursday of this week (1 and 2 February). Early in the morning, just before dawn, is the optimum time to view the comet.

How can I see the ‘green’ comet?

However, don’t expect to necessarily be blown away by what you’re seeing if you’re attempting to view the comet with the naked eye, especially if you live in a built up area.

If the sky is sufficiently dark, you may be able to see the comet as a little diffuse smudge with your naked eye, but most people will at least need a pair of binoculars to get a half-decent glimpse of it.

Nasa has said the comet “isn’t expected” to be quite the spectacle that Comet Neowise was back in 2020, but “it’s still an awesome opportunity to make a personal connection with an icy visitor from the distant outer Solar System.”

Where in the sky can I see the comet?

Anyone seeking to observe the E3 comet is advised by astronomers to choose a dim location free of ambient light, and to give their eyes 30 minutes to acclimatise to the conditions.

The comet is visible in the northern hemisphere below and to the left of the handle of the Plough constellation - weather permitting, of course. It will sail by the pole star, which is the brightest star in Ursa Minor.

In terms of pinpointing the comet’s location within the night sky, there are specialised smartphone apps and websites available - such as Star Chart, Sky Safari and SkyView - which can help you track a variety of celestial objects - including comets.

Professor Don Pollacco, Physics, University of Warwick, said: “Comet 2022 E3 ZTF is an ancient visitor from deep space returning to the Sun’s neighbourhood on a once every 50,000-year visit. It should be just about visible without any optical aid as a faint smudge but only in a very dark sky (with no moon above the horizon).

“If you are lucky you’ll notice its fan shaped head and dusty tail. With some binoculars you may glimpse the longer straight tail. This comet is unusual in that deep images show its head to be bright green – you’ll not see that by eye. The green colour comes from ejected carbon molecules from the comet’s nucleus.”