For the past five months, astronomers around the world have meticulously tracked a strange visitor from another solar system as it zips through our own. Now, it’s about to make its closest approach to Earth.
Interstellar comet 3I/ATLAS will fly by our planet at a safe distance of 1.8 astronomical units (roughly 167 million miles or 270 million kilometers) at 1 a.m. ET on Friday, December 19, according to calculations by NASA’s Jet Propulsion Laboratory. That’s about twice the average difference between Earth and the Sun.
You won’t be able to see 3I/ATLAS with the naked eye, but you could catch a fuzzy, faint glimpse of it in the predawn sky through a powerful pair of binoculars or a backyard telescope.
If you want a clearer view, the Virtual Telescope Project 2.0 will host a livestream of the flyby starting at 11 p.m. ET on Thursday, December 18, and you can watch it below. This astronomical program, overseen by the Bellatrix Astronomical Observatory in Italy, uses remotely controlled telescopes to provide real-time observations of space.
The epic journey of 3I/ATLAS
This comet is considered “interstellar” because it hails from another star system. 3I/ATLAS is only the third interstellar object astronomers have ever discovered, following ‘Oumuamua in 2017 and 2I/Borisov in 2019. Spotting one offers a rare opportunity for researchers to study a literal sample from a far-off corner of the galaxy that current spacecraft can’t reach.
3I/ATLAS’s Friday fly-by will be especially valuable for science. This will be astronomers’ best opportunity to observe the comet and gather data before it leaves our solar system for good. In the months since the NASA-funded ATLAS observatory discovered 3I/ATLAS on July 1, researchers have been working tirelessly to study its chemistry and composition.
Their findings have led to multiple hypotheses about 3I/ATLAS’s origin. One early study suggested it came from an ancient star system in a region of the Milky Way called the thick disk. This region surrounds the thin disk (where our solar system lies) and contains older stars. A later study contradicted this idea, pointing to the thin disk instead.
Even if astronomers can’t narrow down 3I/ATLAS’s origin any further, studying its characteristics can tell us more about what its home system is like. For example, researchers have found that the comet is chock-full of carbon dioxide, suggesting it formed in an environment with higher levels of radiation than our solar system.
3I/ATLAS is zooming through space incredibly fast—it reached its maximum speed of 153,000 miles per hour (246,000 kilometers per hour) when it made its closest approach to the Sun in late October. After Friday, it will slowly fade into the distance as it travels deeper into the outer solar system, so you won’t want to miss this opportunity to see it up close—relatively speaking.
The stargazer’s guide to seeing 3I/ATLAS
If you want to observe 3I/ATLAS with your own telescope or binoculars, here’s everything you need to know.
Your best chance of spotting the comet will be during the pre-dawn hours, about 90 minutes before sunrise. According to BBC Sky at Night Magazine, you can locate it in the morning sky by finding the constellation Leo, then looking toward the lower left of its brightest star, Regulus, and the Sickle asterism.
More specifically, you’ll need to star-hop with your telescope from Regulus to the magnitude 3.8 star Rho Leonis, then look half that distance in the same direction until you see a small, misty smudge. With binoculars, it will appear even fainter.
There are plenty of astronomy apps available to help you locate the comet, such as Stellarium or SkyView. But if you want to save yourself the trouble, you can see 3I/ATLAS in more detail via the Virtual Telescope Project’s livestream. No matter how you choose to watch, witnessing such a rare and scientifically spectacular event will be well worth it.
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