Two green comets visible in Northern Hemisphere as Orionids peak

Two green comets are visible in the Northern Hemisphere sky this week and are expected to be at their brightest around October 20 to 21, offering a rare double display that coincides with the peak of the Orionid meteor shower. Comet C/2025 A6 Lemmon is appearing low in the northwest after sunset and also before dawn, while Comet C/2025 R2 SWAN is visible low in the southwest after dark.

Both comets originate in the solar system's outer regions, likely the Oort Cloud, and have brightened as they approach the inner solar system. Comet Lemmon was first detected in January by the Mount Lemmon Survey in Arizona and has an estimated orbital period of roughly 1,350 years; astronomers say a recent close pass by Jupiter will shorten that period to about 1,150 years. SWAN was identified in September from images taken by a spacecraft instrument and amateur observers. At closest approach this week the comets remain many millions of miles from Earth and pose no hazard.

Sky brightness measurements place Lemmon at roughly fifth magnitude and SWAN slightly dimmer, making both most readily seen with binoculars or from dark rural skies. Observers in light-polluted cities will likely need optical...