How to see interstellar comet 3I/ATLAS as it passes Earth for the last time
This week, backyard astronomers will have their last chance to see interstellar comet 3I/ATLAS before it heads back into space.
An image of interstellar comet 3I/ATLAS taken by the Hubble Space Telescope on July 21, 2025, when the comet was 226 million miles from Earth.
NASA, ESA, D. Jewitt (UCLA); Image processing: J. DePasquale (STScI)
A comet from another star system is set to make its closest and final approach to Earth this week before continuing its journey back into interstellar space.
Interstellar comet 3I/ATLAS will pass within 167 million miles of our planet on Friday and appear as a bright star in the night sky. By comparison, Mars is currently about 250 million miles from Earth. Eager skywatchers armed with good binoculars or a home telescope should be able to spot the comet—and, of course, astronomers are watching closely.
Scientists were study 3I/ATLAS since its discovery in July, but Friday offers the best opportunity to observe the comet: As only the third random object known to enter our solar system from interstellar space, 3I/ATLAS holds clues about how solar systems form in other parts of the universe. United Nations International Asteroid Warning Network is also monitoring 3I/ATLAS, tracking its path across the sky in an attempt to enhance planetary defenses against so-called near-Earth objects such as comets and asteroids.
About supporting science journalism
If you enjoyed this article, please consider supporting our award-winning journalism. subscription. By purchasing a subscription, you help ensure a future of influential stories about the discoveries and ideas shaping our world today.
It remains the mystery of where 3I/ATLAS came from. Like the other two interstellar visitors, the comet is moving on a hyperbolic trajectory, meaning it is moving too fast to be gravitationally bound to our Sun. When it was discovered, it was traveling at about 137,000 miles per hour – almost 40 miles per second. “It's like looking at a rifle bullet for a thousandth of a second,” said astronomer David Jewitt, who observed the comet with the Hubble Space Telescope. at NASA earlier this year. “You can't project it back with any precision to figure out where it started.”
Astronomers hope Friday's approach will shed some light on this interstellar stranger. For example, the dust and gas that a comet released as the sun heated its icy interior can provide clues about how it formed. The Virtual Telescope project plans live broadcast approach will begin at 11:00 pm EST on December 18th.
It's time to stand up for science
If you liked this article, I would like to ask for your support. Scientific American has been a champion of science and industry for 180 years, and now may be the most critical moment in that two-century history.
I was Scientific American I have been a subscriber since I was 12, and it has helped shape my view of the world. science always educates and delights me, instills a sense of awe in front of our vast and beautiful universe. I hope it does the same for you.
If you subscribe to Scientific Americanyou help ensure our coverage focuses on meaningful research and discovery; that we have the resources to report on decisions that threaten laboratories across the US; and that we support both aspiring and working scientists at a time when the value of science itself too often goes unrecognized.
In return you receive important news, fascinating podcastsbrilliant infographics, newsletters you can't missvideos worth watching challenging gamesand the world's best scientific articles and reporting. You can even give someone a subscription.
There has never been a more important time for us to stand up and show why science matters. I hope you will support us in this mission.
