Skywatchers in the Northern Hemisphere are in for a treat as two vibrant green comets are currently gracing our skies. Comet Lemmon and Comet SWAN originate from the distant reaches of the solar system, potentially from the Oort Cloud, which lies beyond Pluto.
Comet Lemmon, known as C/2025 A6, is set to make its closest approach to Earth on Tuesday, while Comet SWAN, designated as C/2025 R2, is expected to pass on Monday but will begin moving away from the sun and likely become dimmer in the coming days.
Carson Fuls, director of a sky survey at the University of Arizona that identified Comet Lemmon, noted that witnessing two comets simultaneously without optical aid is uncommon, though not unheard of. For optimal viewing, skygazers should head outside just after sunset, looking to the northern sky for Comet Lemmon near the horizon, while Comet SWAN will be visible to the southwest.
Experts, including astronomer Valerie Rapson from the State University of New York at Oneonta, advise that both comets may remain observable with binoculars throughout the month, though their brightness is yet to be determined.
These celestial objects are remnants from the solar system’s formation billions of years ago, heating up as they approach the sun, which causes them to emit their characteristic tails. Comet Lemmon was discovered in January during a survey for near-Earth asteroids, while Comet SWAN was detected in September by an amateur astronomer utilizing images from a NASA and European Space Agency spacecraft.
The green appearance of the comets is attributed to gases released from their surfaces, though they will appear as grayish, fuzzy patches from Earth. This event is a reminder of the fascinating dynamic nature of our solar system, following the breakup of another green comet earlier this year and the successful passage of notable comets like Tsuchinshan-Atlas in 2024 and Neowise in 2020.
Overall, the visibility of these comets serves as a captivating opportunity for sky enthusiasts and scientists alike, offering a glimpse into the remnants of our cosmic history.