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Astronomy: How to spot 'green comet' C/2022 E3 (ZTF) in the sky

cometImage source, Dan Bartlett/NASA

Get your binoculars out, because what could be the best comet of 2023 is expected to make an appearance in our skies today.

Comet C/2022 E3 (ZTF) was first sighted in March 2022, when it was passing Jupiter's orbit.

What makes this comet so special is its colour - it's green!

Astronomers say the object, which last passed Earth around 50,000 years ago, is expected to reach its closest point to Earth very soon, which is around 41 million km (26 million miles) away.

When it was discovered, astronomers spotted that something was happening to the comet - that its tail appears to be falling off.

Strong solar wind has separated the head of the comet from its tail (which is a stream of dust and gas produced by intense heat that trails behind the comet).

Scientists call this a "disconnection event".

Image source, Michael Jager / Twitter
Image caption,

This comet-hunter snapped a photo of the tail coming away from the head of the comet

How can I see the comet?

It's difficult to predict just how bright a comet will appear in the sky, but the best time to view Comet C/2022 E3 (ZTF) will be in the early hours of Thursday morning when the Moon has set, according to experts.

Those hoping to catch a really clear view of a green comet passing through the sky are unlikely to see something so striking.

It's because it's brightness is right at the limit of what is visible to the naked eye.

Media caption,

Beginner's guide to astronomy

Coloured space objects like this are likely to show up better on digital cameras which are more sensitive to colour, but this doesn't mean people who a keen to catch a glimpse of the comet in real time won't be able to see it.

Those with binoculars or a small telescope have a better chance of spotting the comet which will appear as a faint white blur.

Light pollution and how dark the sky is can also impact how clearly a comet can be seen, so looking out for the space object in a place that's really dark is likely to provide a better view.

"If you're lucky, you'll see a hint of the tail coming off it, so it'll look more like a classic comet," said says Dr Robert Massey who is the deputy executive director of the Royal Astronomical Society.

Image source, kiankhoon/getty
Image caption,

You should already be able to see the comet with a telescope if you have one, but if you don't, it's predicted it will get bright enough to see with the naked eye

How did the green comet get its name?

The Zwicky Transient Facility in California discovered C/2022 E3 (ZTF), which is why its name has the 'ZTF' acronym at the end.

You may have seen other comets containing this acronym - that's because they were discovered by the same facility.

Image source, solarseven/getty
Image caption,

This illustration shows the long 'tail' of a comet caused by the ice melting up and gas being released

Comet fact file
  • Comets are balls of rock and ice

  • Because of this, they're sometimes referred to as 'dirty snowballs'

  • The ice melts as the comet gets closer to the Sun, producing their signature 'tail'

Where did the green comet come from?

The comet started its epic voyage from the Oort Cloud, a collection of icy objects on the furthest edge of our solar system.

Well, sort of - it's predicted by scientists in the know that there's a group of icy objects out there, but while there's lots of evidence to back the theory up, it can't be observed and therefore hasn't been fully proven.

Predictions show the Oort Cloud may contain more than a trillion icy objects.

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