Two Comets in the Same Sky! - October 2025

During the month of October, there will be not one, but two comets in the western sky. Although not unheard of, it is very rare for more than one bright comet to be visible in the same section of the sky at the same time. But next month, comets C/2025 A6 (Lemmon) and C/2025 R2 (SWAN) will be visible in the western sky about 30 minutes to an hour after sunset. Lemmon is expected to be the brighter of the two.

As seen in the diagram below, Lemmon (yellow path) moves from very low in the NW on Oct 11 to a more favorable position (20 degrees above the horizon) on the 21st. While comet SWAN (blue path) rises steeply from Oct 6 to Oct 21 and into November. 

SWAN will continue to rise high in the sky over the weeks to come, and although it will be decreasing in brightness a little bit (as it moves farther from the sun) it will be in dark skies and will remain visible with optical aid through November. Lemmon is in an orbit that limits its continued view for the northern hemisphere as it will start to sink lower in the sky soon after Oct 30. 

How bright will these be? That's a good question, and difficult to answer. Best estimates are looking good, however, especially for Lemmon.

On October 21st, comet Lemmon will be closest to Earth, very well placed in the sky and may reach magnitude 3.0, a very bright comet indeed! Anything under magnitude 6.0 is visible with the naked eye in good dark locations (brightness goes up as the magnitude number decreases). If it actually reaches that brightness it will be very easy to see with the unaided eye. On November 8th it reaches perihelion (closest to sun) and will be a little brighter but also lower in the sky. You'll need to view it 30 minutes after sunset (6:30pm). 

Comet Lemmon - October 21, 2025 - 7:20pm

Comet SWAN on the other hand remains at about magnitude 7.0 throughout its appearance. But it is a newly discovered comet, and the jury is still out on the magnitude estimates.

Comet SWAN - October 21, 2025 - 7:20pm

Binoculars will enhance the view for both of these and may be required to see comet SWAN. I'll post updates on or around October 5 when more data comes becomes available.