Brightest comet of 2025 might already be on the way

Brightest comet of 2025?

What might be the brightest comet of the year is already approaching the sun. Comet ATLAS C/2024 G3 will come within 8.3 million miles (13.5 million kilometers) of the sun – during perihelion – on January 13, 2025. That’s just 0.09 astronomical units (AU) from the sun. Will it survive the flyby? It’s too soon to say, but its close pass means it might shine brighter than Venus. The best views will be in Southern Hemisphere skies after sunset in mid-January.

The Asteroid Terrestrial-impact Last Alert System (ATLAS) discovered the comet that now bears its name on April 5, 2024. This long-period comet takes about 160,000 years to orbit the sun. Astronomers believe it probably did pass the sun once before, so that might increase its odds of surviving another close encounter.

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How bright will Comet ATLAS be?

The website In-the-Sky predicts the comet could become as bright as magnitude -6.9 on January 13, 2025. An object that bright would be visible in the daytime sky, but in this case the comet will be just so close to the sun that it will be dangerous to look for it in daylight. Other magnitude estimates are a bit lower. For example, G. van Buitenen’s excellent website lists Comet ATLAS’s peak magnitude at -3.9. But that’s still brighter than any star (not counting the sun).

The comet will come within 5 degrees of the sun from our point of view. That’s the amount of sky you can cover with three fingers held at arm’s length. And the comet will stay relatively close to the sun (from our point of view) for a couple days on either side of perihelion.

How to see Comet ATLAS

If you live in the Southern Hemisphere, look for the comet immediately after sunset from mid-January and for the rest of the month. It will be extremely low in the sky at first, still near the sun. And as it gets higher in the sky it will dim, making it more challenging. You may first catch it on January 16 as it starts to leave the sun’s glare.

But if it brightens as much as predictions say, it could still be visible to the unaided eye in the southern evening sky through January.

For the 90% of the population that lives north of the equator, the comet will be sinking to the south as it exits the sun’s vicinity. Those farther south in the Northern Hemisphere might have a better shot to see it just after perihelion, looking after sunset. And perhaps if ATLAS has a long tail, we’ll be able to see the tail after sunset even when the head of the comet is blocked by the horizon. It’s happened before, like with Comet McNaught.

Will Comet ATLAS G3 be the brightest comet of 2025? We’ll know soon!

If you catch an image of Comet ATLAS G3, submit it to us here.

Bottom line: Comet ATLAS G3 might be the brightest comet of 2025. Even so, it will be challenging to spot because it will be so close to the sun.

Via IAU