Want to see the 'Devil Comet' at its brightest? If you miss it, you'll have to wait another 71 years

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This week is the best time for Australians to see a comet that won't be back again for 71 years — almost a whole lifetime.

The so-called "Devil Comet", or 12P/Pons-Brooks has already been visible to Northern Hemisphere viewers, but it's just become visible in the southern sky.

So, grab some binoculars and a camera and find somewhere where you can view the night sky without too much light pollution.

"There's been some astonishingly beautiful photos coming out on social media of the comet taken from the Northern Hemisphere near the Andromeda Galaxy," Jonti Horner, an astronomer with the University of Southern Queensland, says.

In the Southern Hemisphere, we've had to wait a bit longer for the comet to arrive as it moves into our part of the sky, but it should be at its brightest this weekend.

And then you should be able to watch it over the next few weeks as it travels back into the far Solar System

It's worth getting somewhere dark to try and catch a glimpse of the comet, as it won't be back for another 70 years from now.

12P/Pons-Brooks will travel from the top of the Solar System, and exit through the bottom.(theskylive.com/Jacinta Bowler)

12P/Pons-Brooks is a Halley-type comet. Just like Halley's comet, it only comes close to Earth every few decades — Halley's takes 75 years, compared to 12P/Pons-Brooks's 71-year orbit. 

Despite its ominous name, there's no threat to Earth — it's much too far away to hit us.

The comet's closest approach to Earth will be on June 2nd, reaching within 231 million kilometres of the planet — about 1.5 times the distances from the Earth to the Sun.  

When is the best time to see it?

If you're a keen stargazer, the most important date to put in your calender to be able to see the comet is April 21.

This is when the comet will be closest to the Sun (or perihelion) and at its brightest. It will reach a "magnitude" — a logarithmic measurement of brightness used by astronomers — of around 4.5.  

This is enough to see with the naked eye, but less bright than the brightest stars in the sky, which have a magnitude of -1. 

Professor Horner says the comet will "look like a bit of a fuzzy blob" to the naked eye, and its tail may also be visible in dark locations.

"That's with the caveat that there is a famous saying: 'Comets are like cats — they've got tails and they do what they want.'"

Why is it called the 'Devil Comet'?

While most comets are made up of dust, rock, ice and gas, researchers believe 12P/Pons-Brooks is a cryovolcanic comet. This means the ice, dust and gas erupt when the Sun's heat increases pressure on the inside of the comet. 

"As it's been coming in towards the Sun and heating up, it's been periodically giving out bursts or explosions of activity, throwing gas and dust out and then slowing down again," Professor Horner says.

"[Over] the last 12 months or so it keeps burping, it keeps having outbursts."

At one stage, the outbursts caused the comet to look like it had two tails, giving it a horned appearance. 

The comet with 'devil horns' in July 2023, a week after an outburst occurred. (Wikimedia Commons: Juan lacruz, CC-BY-SA-4.0)

Unfortunately, stargazers are unlikely to see the horns now, as recent outbursts have given the comet a more conventional appearance.

It's hard to measure how large the comet is from so far away, and therefore how large the outbursts are, but estimates have put 12P/Pons-Brooks at about 17 kilometres on it's longest side.  

We do know that these bright, cryovolcanic outbursts may get more violent as the comet approaches the Sun.

But Professor Horner says the outbursts themselves will actually appear less bright, due to the relative increase in brightness of sunlight striking the comet.

This makes it hard to predict how bright the comet will appear to viewers on Earth, he adds.

"There's a chance that the comet will be a bit brighter than predicted or equally, it could be a bit fainter than predicted."

How to see 12P/Pons-Brooks

Astronomers suggest you look for the comet just after sunset, as it will be visible close to the western horizon near Jupiter. 

Although the advice varies depending on your location around Australia, about 60 minutes after sunset is the comet-viewing sweet spot, when it's dark enough to see the stars, and 12P/Pons-Brooks itself isn't too low on the horizon.

"Go and find somewhere dark, away from city lights," advises Donna Burton, an astronomer at the Milroy Observatory. 

Pons-Brooks will be just above Jupiter in the night sky on April 21.(Stellarium/ABC)

She suggests using a free app like Star Walk or Night Sky as "they'll show you exactly where it is".

"You don't need people like me to teach you how to find things in the sky anymore."

Although the comet will be visible with the naked eye, Ms Burton suggests taking a pair of binoculars just in case, as you'll be more likely to see the tail and other features of the comet. 

"It's still bright enough to see with your naked eye. But it's not going to be super-bright like some media outlets are making it out to be."

More comet watching on the horizon

While you won't want to miss checking out 12P/Pons-Brooks before it sails off for another 71 years, there might be another comet on the horizon. 

Comet C/2023 A3 (Tsuchinshan-ATLAS) was discovered last year, and it's already got astronomers excited.

According to their models, it will come within just 59 million kilometres of the Sun by September this year. That's twice as close to the Sun as 12P/Pons-Brooks will come this time around.

Even better, the comet will be best seen in the Southern Hemisphere because of the time of year and position of the comet entering the inner Solar System. 

The comet C/2023 A3 in February 2023, soon after it was discovered.(Wikimedia Commons: Filipp Romanov, CC BY SA 4.0)

It's already quite bright even out past Jupiter, so if it stays on track we could be in for a treat when it arrives. 

"I'm cautiously optimistic. It's behaving really well and could become as much 100 times brighter than Pons-Brooks," Professor Horner says.

"But it's a comet we've never seen before, it's never come through the inner Solar System. It's what we'd call a long period comet. And they're even more notorious for being hard to predict."

Posted 16 Apr 202416 Apr 2024Tue 16 Apr 2024 at 8:00pm, updated 17 Apr 202417 Apr 2024Wed 17 Apr 2024 at 12:13am