Filenews 10 October 2025
Two newly discovered comets are expected to approach Earth this month, offering a spectacular celestial spectacle for astronomers and space enthusiasts.
Comets are made up of ice, frozen gases and rocks, and as they travel close to stars such as the sun, the heat causes them to release gas and dust, which creates their characteristic tails.
Researchers spotted comet C/2025 A6 Lemmon on Jan. 3, while C/2025 R2 SWAN was recently spotted for the first time on Sept. 10 during its close approach to the sun, according to Qicheng Zhang, a postdoctoral researcher who studies small-body astronomy at the Lowell Observatory in Flagstaff, Arizona.
For enthusiastic skywatchers, it's a good time to spot comets with binoculars or telescopes because they both have long-period, oval orbits that take them around the sun, meaning they'll only be close to Earth for a limited time.
Comet SWAN will not reappear for another 650 to 700 years, while Lemmon will remain out of sight for 1,300 years, said Carrie Holt, a postdoctoral researcher and astronomer at the Las Cumbres Observatory, a global network of observatories.
"SWAN is only visible in the early evening — as soon as it gets dark," Quanzhi Ye, an associate researcher in the department of astronomy at the University of Maryland, wrote in an email. "Lemmon is now visible just before sunrise, but soon it will only be visible in the evenings and nights."
Both comets appear close to the sun as seen from Earth, so there's only a short amount of time each day to observe them, Ye added.
SWAN will make its closest approach to Earth — at a distance of 38.6 million kilometers from us — on October 20, while Lemmon will oscillate at a distance of 88.5 million kilometers from our planet on October 21, Ye said.
Both comets look similar in the images, surrounded by green gas with long tails flowing behind them, Zhang said.
Astronomers are trying to observe both to learn more about long-period comets, which have orbits that last 200 years or more.
Long-period comets have spent most of their time on the icy 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 push on the outskirts of our solar system billions of years ago – where they have been kept in deep freezing ever since, he added.
"When someone is pushed back toward the sun, we see materials that have changed little since the beginning of the solar system," Holt wrote in an email. "As their ice begins to turn from solid to gas, we get a glimpse of the original building blocks of our solar system and have the opportunity to learn how planetary systems like ours come together."
Characteristics of comets
Comet Lemmon is visible to those living in the Northern Hemisphere, while SWAN favours skywatchers in the Southern Hemisphere – but it is also becoming visible in the Northern Hemisphere, Ye said.
Lemmon is expected to get brighter in the coming weeks through early November, while SWAN will likely fade soon, he added.
Also, Comet Lemmon will hide behind the sun in November and December, and then only become visible to observers in the Southern Hemisphere.
Ukrainian amateur astronomer Vladimir Bezugli discovered Comet SWAN through images taken by the Solar Wind ANisotropies instrument aboard the Solar and Heliospheric Observatory, a joint NASA and European Space Agency program to study the sun.
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 danger to Earth.
How to spot comets
Holt recommends that people use binoculars and observe from a dark area away from light pollution. A host of applications can show where comets are in real time, he said.
"You can even try to see it with your phone's camera," Holt said, "by changing the settings to a longer exposure of a few seconds and aiming it at the sky."
If the skies aren't clear in your area on the night of October 20, the Virtual Telescope Project will share a live broadcast of both comets from telescopes under the dark sky in Manciano, Italy.
