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One of only three known interstellar objects ever detected is making a one-time pass through our solar system. Known as comet 3I/ATLAS, it originated around another star and will reach its closest approach to Earth in the early hours of December 19. Here’s everything you need to know to catch a glimpse of the comet tonight.
What is comet 3I/ATLAS?
3I/ATLAS is a comet, a ball of ice, dust, and frozen gases—or a “cosmic snowball,” as NASA calls them. As they approach the sun, they heat up and develop the long tails characteristic of most comets. The vast majority of the comets we see originate from the Kuiper Belt or the Oort Cloud, two distant regions within our solar system. But comet 3I/ATLAS formed elsewhere in the galaxy and is only passing by. Once it exits our solar system, it will never return.
(Interstellar comet 31/ATLAS is a weirdo, but it’s definitely not aliens.)
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Scientists first spotted 3I/ATLAS in images taken in June 2025 with the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope in Rio Hurtado, Chile, a project funded by NASA. They reported the discovery on July 1.
Since then, space agencies and observatories around the world have trained their instruments on 3I/ATLAS to study it during its flyby—it’s a rare opportunity to examine material from outside our solar system, offering insight into planetary formation around another star. Observations conclude that 3I/ATLAS likely has a diameter between 1,000 feet (320 meters) and 3.5 miles (5.6 kilometers) and is traveling at 130,000 miles (209,000 kilometers) per hour.
When and where to look for comet 3I/ATLAS
At 1 a.m. EST (6 a.m. GMT) on December 19, 3I/ATLAS will reach its closest point to Earth: about 168 million miles (270 million kilometers), or nearly twice the average distance between the Earth and the sun. (It’s worthwhile to note that there is zero risk that 3I/ATLAS will strike Earth.) You will, however, be able to see the comet before and after this time—the comet will likely be visible for several more months, though it will be fading as time progresses.
(We caught a view of an interstellar comet from Mars.)
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But tonight provides the closest look at the interstellar visitor. 3I/ATLAS won’t be visible to the naked eye or weaker binoculars; your best bet to observe the comet is through a telescope, whether one in your backyard or at a local observatory. You can also use skywatching apps to pinpoint the location of 3I/ATLAS in the night sky.
It can currently be found in the constellation Leo, somewhat near its brightest star, Regulus. Keep in mind that 3I/ATLAS may not be visible in the night sky at the exact time of its closest approach to Earth, depending on your location. On the East Coast, for instance, 3I/ATLAS will be easiest to spot in the pre-dawn hours, as it’ll be highest in the sky.
How to live stream a view of comet 3I/ATLAS
If you aren’t able to see 3I/ATLAS at home, you can tune into a live stream by The Virtual Telescope Project, which will feature views from telescopes in Manciano, Italy. The broadcast is scheduled to begin at 11 p.m. EST on December 18 (4:00 GMT on December 19) but is subject to weather conditions at the observation site.
