A comet from beyond our solar system is paying Earth a brief visit — and in the early hours of Friday, December 19, 2025, it reaches its closest point to our planet. The object, known as interstellar comet 3I/ATLAS, is only the third confirmed interstellar visitor ever detected passing through the solar system, making this a rare moment for astronomers and a compelling target for serious backyard observers.
“Interstellar” means exactly what it sounds like: 3I/ATLAS did not form around our Sun. It likely originated around another star, then drifted into the solar system on a fast, one-way path. Unlike most comets, which come from the Kuiper Belt or the distant Oort Cloud, this one is not gravitationally bound to the Sun — once it moves on, it will not loop back for an encore.
The comet was discovered by the ATLAS survey system (Asteroid Terrestrial-impact Last Alert System), a NASA-funded network designed to spot moving objects in the sky. Follow-up measurements quickly showed something unusual: 3I/ATLAS was traveling too fast — and along a trajectory too extreme — to belong to the solar system. Since then, observatories around the world have been tracking it closely, hoping to squeeze out every clue possible about its composition and behavior while it remains within range.
When is the closest approach? The timing matters slightly depending on where you live — and how early you’re willing to get up. NASA’s orbit calculations place the closest approach at 1:00 a.m. ET in the United States, which is 6:00 a.m. GMT in the UK, on December 19. At that moment, the comet will be about 1.8 astronomical units away — roughly 168 million miles (270 million kilometers). In other words: it’s nowhere near Earth in any practical sense, and there is no risk to the planet.
US timing: For many Americans, the best chance comes in the late-night to pre-dawn window — especially as the comet climbs higher in the sky before sunrise. UK timing: In Britain, you’re looking at the early morning hours before daylight, when the sky is still dark enough for telescope work.
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Where to look: Right now, 3I/ATLAS is positioned in the constellation Leo, not far from Regulus, Leo’s brightest star. That doesn’t mean you’ll simply “spot it near Regulus” by eye — but it does give you a starting point. The comet’s exact position shifts night to night, so your most reliable strategy is to use a skywatching app (or a finder chart from an observatory) to pinpoint its current coordinates.
What you’ll actually see: Expectations matter. 3I/ATLAS is not a dramatic naked-eye comet, and it won’t look like the long, bright tail photos shared online. Those images are usually made with long exposures and careful processing. For most amateur observers, the comet is likely to appear as a small, faint smudge or a fast-moving greenish point depending on your optics and sky conditions — a subtle target rather than a fireworks show.
What you need to see it: Your best bet is a telescope (a modest backyard scope can work under dark skies, but bigger aperture helps). Binoculars generally won’t be enough unless conditions are unusually good. If you have access to a local astronomy club or observatory, this is exactly the kind of event they may organize a viewing session around — and they’ll usually have the right equipment, plus experienced people who know how to locate faint objects quickly.
Why scientists are excited: Interstellar objects offer a rare chance to study material formed in a different planetary system. As the comet warms, it releases gas and dust into a thin atmosphere (the coma) that can be analyzed for chemical fingerprints. NASA notes that comets are “cosmic snowballs” of frozen gases, rock, and dust — and in this case, the snowball comes from another star’s neighborhood, carrying information we can’t get any other way.
Can you watch it online? Yes. If you don’t have a telescope, or the weather refuses to cooperate, a livestream is often the most satisfying option. The Virtual Telescope Project has scheduled coverage beginning at 11:00 p.m. ET on Thursday, Dec. 18 (that’s 4:00 a.m. GMT on Friday, Dec. 19), though any live astronomy broadcast is at the mercy of clouds.
The comet will remain observable for a while yet, but it is expected to gradually fade as it heads back toward interstellar space. For observers, that makes this week’s pass the sweet spot: close enough to be worth the effort, rare enough to feel like a genuine “you’re seeing history” moment — even if what you see is only a faint dot that happens to have travelled for eons to reach our sky.
Helpful links: NASA: Comet 3I/ATLAS overview | Space.com: Exact closest-approach time and distance
