Astronomers are encouraging people to look for a "once-in-a-lifetime" comet this week.

Comet Nishimura is set to fly past the Earth at 240,000 miles per hour early on Tuesday (September 12). 

The comet is already visible in the sky with binoculars or a telescope, but Tuesday is set to present people with their best chance to see it with the naked eye.

When is the best time to see Comet Nishimura?

The best time to see the comet is in the hour after sunset and the hour before dawn by looking east-north-east, towards the crescent moon and Venus.

What is known about Comet Nishimura?

Comet Nishimura - or C/2023 P1 - was only discovered last month on August 11.

Hideo Nishimura, a Japanese astrophotographer, caught it on camera while taking long-exposure photographs of the sky.

It is the third comet Nishimura has discovered so far.

Professor Brad Gibson, director of the E A Milne Centre for Astrophysics at the University of Hull, believes it could range in size from a few hundred metres to a mile or two in diameter.

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It is thought that the comet could be responsible for an annual meteor shower named the Sigma-Hydrids, which takes place in December every year.

Prof Gibson said: “The comet takes 500 years to orbit the solar system, Earth takes one year, and the outer planets can take many decades.

"So, to say this is a once-in-a-lifetime opportunity to see Nishimura isn’t an exaggeration.”

Where is the best place to see Comet Nishimura in Norfolk?

As a rural county with low levels of light pollution, there are plenty of places to stargaze in Norfolk. 

Wiveton Downs on the north Norfolk coast is a 71-acre Site of Special Scientific Interest.

It is plunged into almost total darkness at night, making it a prime stargazing location.

Kelling Heath Holiday Park in north Norfolk was awarded Dark Sky Discovery Site status in 2017.

Seven stars of the Orion constellation and the Milky Way are visible to the naked eye from the open woodland location.

Barrow Common, situated on the site of a former Second World War radar station just south of Brancaster, was awarded Dark Sky Discovery Site status in 2019.

RSPB Titchwell Marsh, near Hunstanton, is also covered by pitch-black skies at night.

This spot is well-known by avid stargazers, with The King's Lynn and District Astronomy Society choosing it to host taster sessions for new members.

How are comets formed?

Prof Gibson explained comets are “chunks of ice and rock” left over from the formation of the solar system nearly five billion years ago.

As they pass closer to the sun it heats the comet, liberating an icy gas which gives them their distinctive tail.

He said tiny particles of dust and rock from comets are freed by the sun as a comet passes nearby and each year the Earth passes through this debris, leading to meteor showers.