In the upcoming weeks, there will be a unique opportunity to see two comets with a greenish hue as they swing through the inner solar system this autumn.
The comets, C/2025 A6 (Lemmon) and C/2025 R2 (SWAN), are currently visible from the Northern Hemisphere as they circle the sun, passing through our cosmic backyard.
It is extremely rare for two comets to appear in the same month.
Until the end of October, binoculars or small telescopes can be used to view both celestial objects. Comet Lemmon is at its brightest on or around October 21 and may be visible to the unaided eye when it approaches Earth's closest point.
Some skywatchers have already spotted these icy nomads.
In late September, astronomer Julien De Winter, a junior lecturer at the University of Mons in Belgium, took pictures of Comet Lemmon from Texas. He captured the planet's long tail and striking emerald glow.
The comet's nucleus is surrounded by a cloud of gas that contains carbon, which gives it its faint green hue.
According to EarthSky, a website dedicated to astronomy and skywatching, Comet Lemmon will be visible in the Northern Hemisphere from now until midmonth, close to the Big Dipper, before sunrise. In the hours before dawn, it is best to look northeast in the sky, just below the cluster of stars that form the Big Dipper's recognizable bowl and handle.
Instead, the comet will rise in the west and be visible in the evening sky in roughly a week. Although these celestial objects can be difficult to see, it might be possible to see it with the naked eye from that point until the end of the month.
Until the end of the month, Comet SWAN can be seen in the evening sky. It will be most visible facing southwest about 90 minutes after sunset. Binoculars or a small telescope will be required because this comet is probably not going to be bright enough to be seen with the unaided eye.
After sunset, Comet SWAN will rise higher and higher on the horizon over the next few days. It might also become brighter before it approaches Earth's closest point on or around October 20.
Around the end of the month, it might even be possible to see both comets on the same night if the following conditions are met clear skies, dark skies, and as little light pollution as possible.
The Mount Lemmon Survey, which uses telescopes in Arizona's Santa Catalina Mountains to monitor near-Earth objects, made the discovery of Comet Lemmon in January.
The discovery of Comet SWAN was even more recent, having been discovered in early September by an amateur astronomer looking through photos taken by NASA's Solar & Heliospheric Observatory's SWAN instrument. The observatory was launched in 1995 with the goal of orbiting and studying the sun.
This month, another comet type—one from outside our solar system—is also making its way through the inner solar system. Just three such interstellar visitors have been confirmed, including Comet 3I/ATLAS, which was recently photographed by a spacecraft orbiting Mars. On or around Oct. 30, the interstellar comet will approach the sun at its closest point.
