Sky gazers are gearing up for a 'once in a lifetime' opportunity to spot a spectacular and extremely rare green comet.

Comet C/2022 E3 is coming the closest its been to Earth since the last ice age, says NASA.

First discovered by astronomers using a wide-field survey camera back in March 2022 at an observatory in California, excitement is now building at the prospect of being able to see the comet with the naked eye this week.

While the comet has been watched closely by those with telescopes and binoculars since early January, it is set to make its closest approach to Earth on Wednesday (February 1) when there is a chance you won't need any form of telescopic lens to see it.

What is Comet C/2022 E3?

The comet, says the Royal Observatory in Greenwich, is believed to come from the very outskirts of the solar system in the Oort Cloud - an unobserved area estimated by scientists to contain more than a trillion icy objects.

According to the website Space.com it is estimated that the comet, which has been photographed surrounded by a blue green hue, takes 50,000 years to fully orbit the Sun.

This means that prior to it coming within 100 million miles of the Sun on January 12 and an estimated 26 million miles away from Earth by early February, the last time it most likely came this close to our planet was during the Upper Paleolithic period - also called the Old Stone Age because of the development of chipped stone tools - and means that the last humans likely to have spotted C/2022 E3 (ZTF) would have been early homo sapiens alive during the last ice age or glacial period.

Spotting the comet

Comets - says the Royal Observatory - can be unpredictable and so it is hard to say with a high degree of accuracy how bright the comet will be or what it will look like ahead of time.

At present it is also thought the comet won't form a tail that will be visible without a telescope but this could change, say experts.

For now, the comet looks like a fuzzy green ball in the sky with the green haze caused by UV radiation from the Sun lighting up the gases that are streaming off the comet’s surface.

To see the comet for yourself on Wednesday - which is the day being forecast to give the best view weather depending - people will beed to look to the north just after sunset and search for what will appear as a faint greenish glow in the sky.

Anyone hoping to head outside for a look is being advised to avoid areas with high levels of light pollution and instead choose a dark area where skies are not blighted by so many lights from streets and houses.

Under the right dark sky conditions, the comet could be visible to the unaided eye, but binoculars if you have them will no doubt make the job easier.