Two bright comets will swing by Earth this month. Here’s how to see them
By Ashley Strickland, CNN
(CNN) — Two newly discovered comets are streaking across the sky in a spectacular display as they make their closest approaches to Earth this month.
Comets are made of ice, frozen gases and rock, and as they travel near stars such as the sun, heat causes them to release gas and dust, which creates their signature tails.
Researchers spotted the comet C/2025 A6 Lemmon January 3, while C/2025 R2 SWAN was only recently detected for the first time on September 10 during its close approach to the sun, according to Qicheng Zhang, a postdoctoral fellow studying small body astronomy at Lowell Observatory in Flagstaff, Arizona.
For eager sky-gazers, it’s a great time now to spot the comets with binoculars or telescopes because they both have long-period, oval-shaped orbits that take them around the sun, meaning they’ll only be in proximity of Earth for a limited time.
Comet SWAN won’t reappear for another 650 to 700 years, while Lemmon will remain out of sight for 1,300 years, said Carrie Holt, postdoctoral fellow and astronomer at Las Cumbres Observatory, a global network of observatories.
“SWAN is only observable in early evenings — right after the sky has become dark,” wrote Quanzhi Ye, associate research scientist in the department of astronomy at the University of Maryland, in an email. “Lemmon is now visible right before sunrise, but will soon become visible in the evenings and evenings only.”
Both comets appear near the sun as viewed from Earth, so there’s only a short window each day to observe them, Ye added.
Solar system time capsules
SWAN will make its closest approach to Earth — coming within 24 million miles (38.6 million kilometers) of us — on October 20, while Lemmon will swing within 55 million miles (88.5 million kilometers) of our planet on October 21, Ye said.
Both comets appear similar in images, surrounded by green gas with long tails streaming behind them, Zhang said.
Astronomers are trying to observe both to learn more about long-period comets, which have orbits lasting 200 years or longer.
Long-period comets have spent most of their time at the frigid edge of our solar system in the Oort Cloud, a spherical shell of icy bodies, Holt said. These comets likely formed near giant planets such as Jupiter and Saturn before receiving a gravitational kick to the solar system’s outskirts billions of years ago — where they’ve been preserved in deep freeze ever since, she added.
“When one gets nudged back toward the sun, we’re seeing materials that have barely changed since the solar system’s beginning,” wrote Holt in an email. “As their ices start to sublimate (change from a solid to a gas), we get a glimpse of the original building blocks of our solar system and a chance to learn how planetary systems like ours come together.”
A comet double feature
Lemmon is visible to those living in the Northern Hemisphere, while SWAN favors sky-gazers in the Southern Hemisphere — but it’s becoming visible in the Northern Hemisphere, too, Ye said.
Lemmon is expected to brighten a little more in the coming weeks through early November, while SWAN will likely be fading rapidly soon, he added.
Comet Lemmon will hide behind the sun in November and December, then become visible only for observers in the Southern Hemisphere afterward, Ye said.
Ukrainian amateur astronomer Vladimir Bezugly discovered Comet SWAN through images captured by the Solar Wind ANisotropies, or SWAN, instrument aboard the Solar and Heliospheric Observatory spacecraft, a joint NASA-European Space Agency project to study the sun.
Meanwhile, Lemmon was spotted by the Mount Lemmon Observatory in Arizona as part of the Catalina Sky Survey, a NASA-funded project that scans the night sky for near-Earth objects such as asteroids that could pose a risk to Earth.
By chance, the survey is also a great way to find comets, said Carson Fuls, director of the Catalina Sky Survey at the University of Arizona’s Lunar and Planetary Laboratory, who was running the telescope the night of Lemmon’s discovery.
“It was not clear at first that this was a comet,” Fuls said. “It was too dim and too far away to produce the long dramatic tail you see in current images.”
Lemmon may be one of the best comets of the year for observers, Fuls said.
“This one is spectacular because it may be able to be seen from a dark location with only a regular set of binoculars or even the naked eye at its brightest,” he said. “Comets that are this bright and close are rare and an exciting opportunity for everyone to enjoy some backyard astronomy.”
Comet Lemmon — just below brightness for the naked eye now — is rapidly brightening and will likely become at least faintly visible in the next few weeks, Zhang said.
The comet’s closest pass to Earth will present a great viewing opportunity, Fuls said.
“This would be a great time to view it as the moon will be out of the way,” he wrote in an email. “It should be visible for a week on either side of its closest approach, and for longer with the aid of a small telescope.”
How to spot the comets
Holt recommends that people use binoculars and observe from a dark area away from light pollution. A multitude of apps can show where the comets are in real time, she said.
“You can even try to see it with your phone camera,” Holt said, “by changing the settings to a longer exposure of a few seconds and aim it at the sky.”
Free planetarium software such as Stellarium or KStars shows exactly where comets are relative to stars at any moment, Zhang said.
Currently, Lemmon is a bit below the bottom of the Big Dipper, said Teddy Kareta, an assistant professor at Villanova University near Philadelphia.
If skies aren’t clear in your area on the evening of October 20, The Virtual Telescope Project will be sharing a livestream of both comets from telescopes beneath dark skies in Manciano, Italy.
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