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.)
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.
