Topline
Two green comets — Lemmon (C/2025 A6) and SWAN (C/2025 R2) — are becoming visible from the Northern Hemisphere in binoculars or a small telescope. They’ll get brighter around Oct. 20-23 as the Orionid meteor shower peaks, but comet Lemmon in particular is now being widely observed. Here’s how to find them on Saturday, Oct. 11, 2025.
Key Facts
On Saturday, Comet Lemmon will be visible before sunrise in the northeast, close to the Big Dipper, while a 76%-lit waning gibbous moon shines in the west. Comet SWAN will be low in the southwest after sunset.
Comets Lemmon and SWAN are the first comets visible in binoculars since Comet Tsuchinshan-ATLAS in October 2024.
Comet Lemmon has been getting steadily brighter in recent days. Last in the inner solar system around the year 675, its following visit will take place around 3175. Comet SWAN is a much longer-period comet, taking about 22,554 years to orbit the sun. It won’t visit again until 24,579.
Both comets will appear as small, diffuse patches in a pair of binoculars that change position slightly each day. By early next week, Comet Lemmon will also be visible in the post-sunset night sky.
Over the next two weeks, both comets are forecast to become brighter as they both reach their closest to Earth around Oct. 20-23.
Comet Lemmon: When And Where To Find It On Saturday, Oct. 11, 2025
Distance from the sun: 76.8 million miles (123.6 million kilometers)
Distance from Earth: 68.3 million miles (109.9 million kilometers)
On Saturday, Oct. 11, 2025, Comet Lemmon will be visible in the northeast before dawn to the right-hand side of the Big Dipper, low in the sky but observable in binoculars. It will be roughly halfway between the stars Megrez and Phecda on the inside of the Big Dipper’s bowl, and Alula Borealis and Alula Australis, two bright stars that mark the foot of the constellation Ursa Major, “the Great Bear,” according to finder charts on In-The-Sky.com.
Comet Lemmon: Best Time To Look
The best time to look for Comet Lemmon will be a 30-minute window beginning about 90 minutes before sunrise where you are. For New York City, sunrise is 7:03 a.m. EDT, so the ideal viewing time will be 5:33-6:03 a.m. EDT (Venus will rise in the east during this time), although you can look earlier. The comet’s height above the horizon will vary depending on your location, but from New York, it will be around 27 degrees up (about the width of the span of your hand, with fingers stretched out, held at arm’s length) and rising. In addition to fighting the increasing light of dawn, on Thursday, there’s also the light of the 76%-lit waning gibbous moon, setting in the west, to contend with.
Comet Swan: When And Where To Find It On Saturday, Oct. 11, 2025
Distance from the sun: 77.6 million miles (124.9 million kilometers)
Distance from Earth: 29.1 million miles (46.9 million kilometers)
Blueish-green Comet SWAN — only discovered in September — will be visible in binoculars on Saturday, Oct. 11, 2025, low in the southwest after sunset, to the upper-right side of bright star Antares in the constellation Scorpius, according to finder charts on In-The-Sky.com.
Comet Swan: Best Time To Look
The best time to look for Comet SWAN will be a 30-minute window beginning about 90 minutes after sunset where you are. For New York City, sunset is 6:19 p.m. EDT, so the ideal viewing time will be 7:49-8:19 p.m. EDT. The comet’s height above the horizon will vary depending on your location, but from New York, it will be around 15 degrees up (about the width between your little finger and forefinger held at arm’s length) and sinking.
Why Both Comets Are Green
Recent photographs show both comets to be glowing a distinctive green. This color comes from a molecule called dicarbon (C₂), which fluoresces green when broken apart by sunlight in a comet’s coma. According to NASA, the green glow is confined to the comet’s head because the molecule quickly breaks down and doesn’t reach the tail. This makes Lemmon and SWAN look striking in long-exposure photographs, even if they appear fainter to the naked eye.
Why Comets Have Tails
Comets sprout tails as they near the sun. According to NASA, heat turns surface ices into gas, forming a coma, while sunlight and the solar wind push this material outward. That creates two tails — a broad, curved dust tail that reflects sunlight and a straight, bluish ion tail that points directly away from the sun. Some tails can stretch for millions of miles and are always directed away from the sun, no matter the comet’s direction of travel.
Check my feed every day this month for a daily “comet tracker” with finder charts and tips for viewing Comet Lemmon and Comet SWAN.
