Michael Steven Harris, also known as Brighton Astro, spotted Comet Nishimura as he looked up at the night sky in Brighton.
The photographer caught the comet’s green glow from Green Ridge and Westdene Windmill, with its “tail” seen streaking through the sky.
Nishimura was only discovered in August, but will be closest to Earth just before dawn next Tuesday (September 12).
The object, travelling through space at a staggering 240,000mph, is already visible to the naked eye.
Professor Brad Gibson, an astrophysicist at the University of Hull, said that the “once-in-a-lifetime opportunity” can be seen in the hour after sunset and the hour before dawn by looking east-north-east, towards the crescent moon and Venus.
He said: “The comet takes 500 years to orbit the solar system, Earth takes one year, and the outer planets can take many decades.
“Halley’s Comet, which caused much interest during its last nearby visit to Earth in 1986, takes 76 years to orbit the solar system.
“So, to say this is a once-in-a-lifetime opportunity to see Nishimura isn’t an exaggeration.”
Comet C/2023 PI is named after Japanese astrophotographer Hideo Nishimura, who recorded it when he was taking long-exposure photographs of the sky with a digital camera last month.
The comet will pass closest to the sun on September 17, which it may not survive.
Scientists are still trying to estimate Nishimura’s size, but it is thought it could range from a few hundred metres to potentially two miles in diameter.
Comets are fragments 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, the comet heats up, liberating an icy gas which gives them a distinctive tail in the night sky.
There is a debate between scientists over whether it was a comet or an asteroid which caused the extinction of the dinosaurs 65 million years ago.
However, there is no danger of Nishimura colliding with Earth, as astronomers have carefully charted its orbit and speed of travel.