A Double Dose of Comets

Billy Teets
Billy Teets

Oct 28, 2025, 3:17 PM

Comet Lemmon moves against the background stars
Comet C/2025 A6 (Lemmon) was observed from Dyer Observatory just prior to sunrise on October 5, 2025.  These two-minute exposures show how rapidly comets move among the background stars and how quickly the dust tail can change.  Numerous passing satellites left streaks in several of the frames, and the final two frames show significant brightening due to the rising Sun.  North is up, east is to the left, and the field of view is nearly 1.5 degrees tall by a degree wide (three Moons tall by two Moons wide).  Taken with a ZWO ASI6200MM CMOS camera using a luminance filter and an Officina Stellare 16″ RiLA astrograph telescope. Credit: Billy Teets

For those who try to catch fleeting glimpses of comets as they quickly make their way through our solar system, it often seems that folks south of Earth’s equator get frequent good views of comets while their northern neighbors just get to hear about the adventures and see photos. This fall, though, turned out to be a great time for those of us in the Northern Hemisphere to catch a glimpse of not one but two icy visitors.

Comet Lemmon

The current showstopper in terms of comets has to be Comet Lemmon. At the beginning of the month, early birds were able to catch Comet Lemmon in the northeast as it moved past the Big Dipper in the morning sky. With an orbit that kept it well north of the Sun, it sank closer to the northern horizon with each passing day. However, by the third week of October, it had become well positioned in the northwest after sunset to begin its evening apparition as it continued drawing nearer the Sun. By then, it was sporting an impressive tail that was fairly easy to pick up in binoculars.

Comet Lemmon exhibits a tail disconnection event.
Comet C/2025 A6 (Lemmon) was observed from Dyer Observatory just prior to sunrise on October 4, 2025.  These five-minute exposures show how rapidly comets move among the background stars.  Numerous passing satellites left streaks in several of the frames, and the final two frames show significant brightening due to the rising Sun.  One very notable feature is the moving blob of material to the upper right of the coma (the brightest part of the comet). This may be the result of a mass breaking away from the comet’s parent nucleus or an example of a “tail disconnection event,” the result of the Sun’s solar wind interacting with the tail and essentially tearing it from the comet as the solar wind gusted. North is up, east is to the left, and the field of view is nearly 1.5 degrees tall by a degree wide (three Moons tall by two Moons wide).  Taken with a ZWO ASI6200MM CMOS camera using a luminance filter and an Officina Stellare 16″ RiLA astrograph telescope. Credit: Billy Teets

Through the first week of November, it will still be visible low in the western sky after sunset, gradually moving toward the southwest. By the start of the third week of November, Comet Lemmon will begin its plunge toward the horizon as it makes its closest approach to the Sun on November 21. After that, our friends in the Southern Hemisphere will get their turn to see Comet Lemmon as it makes its way out into the far reaches of the solar system, eventually getting about five times farther from us than little Pluto. It will be another thirteen centuries or so before it makes its next visit to the inner solar system, so snag a peek while you can!

Comet Lemmon remains low to the western horizon during November. The map above shows the comet’s position for specific days of November 2025.

Comet SWAN

While we often discover comets as they are making their way to the inner solar system, well before they reach their closest approach to the Sun (perihelion), Comet SWAN was discovered just a day before its perihelion passage by an amateur astronomer observing images from the Solar and Heliospheric Observatory’s (SOHO) Solar Wind Anisotropies (SWAN) camera on September 11, 2025. Over the past few weeks, Comet SWAN has moved farther from the Sun in our sky, reaching its closest point to Earth on October 19. Unlike Comet Lemmon, which is moving closer to our western horizon each day, Comet SWAN is moving higher in the sky, making it easier to catch some last-minute views. It is also on its way back out to the outer solar system, but won’t get as far as Comet Lemmon, and we should see it back in our sky in about 650 years or so. It will continue to dim as it moves away, but binoculars or telescopes at low magnification should enable backyard astronomers to continue to monitor it for a few more weeks.

Comet SWAN's position in the sky for November 2025
Comet SWAN will continue dimming over the next few months, but remains decently high in the sky for observers in the Northern Hemisphere. The comet’s position is highlighted for specific dates in November 2025.

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