Two greenish comets are streaking across the night sky this month
Two greenish-hued comets are passing through the inner solar system this fall, offering a rare chance to spot them in the coming weeks.
The comets, named C/2025 A6 (Lemmon) and C/2025 R2 (SWAN), are now visible from the Northern Hemisphere as their orbits take them through our cosmic backyard on their journey around the sun.
Two comet appearances in the same month are very rare.
Both celestial objects can be observed with binoculars or small telescopes until the end of October. Comet Lemmon could be visible to the naked eye when it reaches its closest point to Earth and will therefore be brightest around October 21.
Some sky watchers have already spotted these icy wanderers.
Astrophotographer Julien De Winter, a lecturer at the University of Mons in Belgium, photographed Comet Lemmon in late September from Texas, capturing its spectacular emerald glow and long tail.
The slight green color comes from the presence of carbon in the gas cloud surrounding the comet’s nucleus.
In the Northern Hemisphere, by mid-month, Comet Lemmon will appear near the Big Dipper before sunrise, according to EarthSky, a sky-gazing and astronomy website. It’s best to look at the sky toward the northeast in the hours before dawn, slightly below the cluster of stars that make up the distinct bowl and shaft of the Big Dipper.
In about a week, the comet will be visible in the evening sky, rising in the west. From this point until the end of the month, it may be possible to see it with the naked eye, but these cosmic objects can be difficult to see.
Comet SWAN can be observed in the evening sky until the end of the month. The best time to spot it will be around 90 minutes after sunset, facing southwest. This comet will probably not be bright enough to be seen with the naked eye, so binoculars or a small telescope will be necessary.
In the coming days, Comet SWAN will appear higher and higher on the horizon after sunset and may become brighter before reaching its closest point to Earth around October 20.
Under ideal conditions – clear weather, dark skies and as little light pollution as possible – it might even be possible to see both comets on the same night towards the end of the month.
Comet Lemmon was discovered in January by the Mount Lemmon Survey, which tracks near-Earth objects using telescopes in Arizona’s Santa Catalina Mountains.
The discovery of comet SWAN was even more recent: an amateur astronomer spotted it in early September while browsing images from NASA’s Solar and Heliospheric Observatory’s SWAN instrument, launched in 1995 for a mission to orbit and study the sun.
A different type of comet – one from outside our solar system – is also passing through the inner solar system this month. Comet 3I/ATLAS is only the third such interstellar visitor ever confirmed, and it was recently photographed by a spacecraft orbiting Mars. The interstellar comet will come closest to the sun around October 30.
