How to spot Nishimura, the green comet in the sky this week

This week, observers in the Northern Hemisphere have a chance to spot a comet whose green tail lights up as it approaches the Sun in the early morning hours. Comet Nishimura, or C/2023 P1, won’t be visible from the Southern Hemisphere until late October.

When should I look for a comet?

Comet Nishimura will be visible in the morning before sunrise until September 17, when it will pass closest to the Sun. Early mornings throughout the week are the best time to view as viewing is difficult when close to the sun. After September 17, if the comet passes close to the Sun, it will be tricky to see in the Northern Hemisphere, but visible from the Southern Hemisphere.

How to spot a comet?

Look northeast an hour before sunrise, and the comet should be low in the sky in Leo. Use a star tracking app to find out exactly where it is from your location.

If you can’t find the comet without any visual aid, try using binoculars so you can make out the shape of the comet’s tail. When it is visible to the naked eye, it may appear as a fuzzy blob. “According to predictions, it will be visible to the naked eye, but well seen telescopes,” says Dan Pollacco of the University of Warwick. “You don’t know comets.”

Is Comet Nishimura Rare?

Comet Nishimura was discovered a month ago by amateur astronomer Hideo Nishimura. It’s so rare – we usually have a great deal of warning between finding a comet and it being visible high in our sky.

Comets visible to the naked eye are not particularly rare; Another green comet passed Earth earlier this year. But this particular one takes 437 years to orbit the Sun, so it won’t return until the year 2423.

Why is Nishimura green?

The comet appears green because its coma, the gas surrounding the nucleus, contains a relatively rare type of carbon gas called diatomic carbon, which consists of two carbon atoms.

What is a comet?

Comets are balls of ice and rock that orbit the Sun from the Oort Cloud, part of the outer Solar System. As they approach the Sun, their ice turns into gas and flows like a tail — sometimes visible to us from Earth. That makes it tricky to predict how easy it will be to see them from Earth.