This weekend provides an incredible opportunity for skywatchers as it offers the last best chance to see two stunning green comets before they disappear amidst the brightness of a waxing moon. On Saturday, October 25, Comet Lemmon (C/2025 A6) will continue its westward journey, entering the constellation Serpens in the northwestern sky. Meanwhile, Comet SWAN (C/2025 R2) will be visible below the Summer Triangle stars in the southern sky, near the planet Saturn. This is the optimal night to catch a glimpse of these celestial wonders before they begin to fade away and the 16%-lit waxing crescent moon starts to illuminate the twilight sky.
The ideal time to observe Comet Lemmon and Comet SWAN on Saturday, October 25, is during a 30-minute window that begins approximately 90 minutes after sunset in your location. Both comets will be visible post-sunset but occupy opposite areas of the sky. For instance, in New York City, where sunset occurs at 5:57 p.m. EDT, the best time for viewing will be from 7:27 p.m. to 7:57 p.m. EDT. During this period, the moon will be low in the southwest, setting early to provide dark conditions, making it easier to spot both comets before the moon's brightness increases later in the week.
Comet Lemmon is currently located at a distance of 59.2 million miles (95.2 million kilometers) from the sun and 57.1 million miles (91.9 million kilometers) from Earth. On the evening of Saturday, October 25, look for Comet Lemmon positioned above the bright star Arcturus, which will be low on the northwest horizon. To locate it, trace the stars in the Big Dipper's curved handle and follow an arc to reach Arcturus. From there, move at a right angle to the next bright star, Rasalhague, the most luminous star in the expansive constellation Ophiuchus. For viewers in New York, Comet Lemmon will appear about 20 degrees above the northwest horizon at 7:27 p.m. EDT and will gradually sink as twilight deepens.
In contrast, Comet SWAN is situated at a distance of 99.7 million miles (160.4 million kilometers) from the sun and 26.9 million miles (43.3 million kilometers) from Earth. This blue-green comet will be observable with the aid of binoculars on Saturday, October 25, positioned low in the south-southwest after sunset. Comet SWAN can be found in the constellation Aquarius, above the "Teapot" asterism of Sagittarius, and below and to the left of the bright star Altair within the Summer Triangle. For those observing from mid-northern latitudes, a simple way to locate it is by looking midway between Altair and the bright star Fomalhaut. In New York, SWAN will be approximately 43° high in the sky at 7:27 p.m. EDT, slowly descending toward the horizon thereafter.
For those eager to track these celestial events, check my feed daily this month for a comet tracker featuring finder charts and viewing tips for both Comet Lemmon and Comet SWAN from mid-northern latitudes. Additionally, explore resources on how to photograph the green comets, the best stargazing apps for locating these comets, and a list of 25 dark sky parks in the U.S. where you can observe the comets in their full glory.
For additional insights, consider these articles: Comet Tracker For Thursday: It’s Finally Time To See Rare Twin Comets, A Once-In-A-Lifetime Green Comet May Soon Be Visible, Scientists Say, and Two Naked Eye Comets, ‘Harvest Moon’ And Fireballs: October’s Night Sky.
