New York – two comets Bright greens are streaking across the skies and are visible to skywatchers in the Northern Hemisphere.
Both come from the far reaches of our solar system, possibly from what is known as the Oort Cloud, far beyond Pluto. Comet Lemmon will have its closest encounter with Earth on or around Tuesday. The other cosmic snowball, Comet SWAN, should have its flyby of Earth on Monday, but it is moving away from the sun and will likely dim as the days go by.
Detecting two comets simultaneously without special equipment is “rare, but not unprecedented,” said Carson Fuls, director of the University of Arizona-based sky survey that detected Comet Lemmon.
To see the pair, go outside just after sunset and look up into the northern sky to see Comet Lemmon near the horizon. Comet SWAN will also be near the horizon, but to the southwest.
The double comets could be visible with binoculars until the end of the month, but experts are still unsure how bright they will remain, said astronomer Valerie Rapson of the State University of New York at Oneonta.
Comets are frozen remnants of the formation of the solar system billions of years ago. They warm up as they approach the sun, releasing their characteristic flowing tails.
Comet Lemmon, also designated C/2025 A6, was discovered in January by a telescope scanning the night sky for near-Earth asteroids. Comet SWAN, also known as C/2025 R2, was discovered in September by an amateur astronomer using photographs from a spacecraft operated by NASA and the European Space Agency.
Comets are green due to the gases that emanate from their surfaces. From Earth, they will look like fuzzy gray patches.
Earlier this year, a green comet broke up as it passed close to the sun, dashing hopes of a naked-eye spectacle. A bright comet called Tsuchinshan-Atlas passed by Earth in 2024, and other notable flybys included Neowise in 2020 and Hale-Bopp and Hyakutake in the 1990s.