An Autumn of Comets

The coming months promise to be a treat for skywatchers. Whether you’re in the northern or southern hemisphere, the night sky will feature a parade of comets—each with its own story and best window of visibility. Thanks to the global Unistellar community, we’ll have the opportunity to follow these icy visitors together.

September: Comet 3I/ATLAS (C/2025 N1)

September’s featured target is Comet 3I/ATLAS, our Solar System’s third known interstellar visitor! Although its extreme trajectory won’t bring this comet to its closest solar approach – called perihelion – until late October, September gives us a chance to observe it before it disappears into the Sun’s glare. After a few weeks’ hiatus, it will return in November, when it will actually be better placed for southern hemisphere observers.

Think of September as our “catch it while you can” month: a fleeting chance to spot this rare object before it slips away temporarily.

October: Comet C/2025 A6 (Lemmon)

October belongs to Comet C/2025 A6 (Lemmon). This comet is expected to brighten dramatically, potentially reaching naked-eye visibility around its closest approach to Earth on October 21st (with perihelion on November 8th).

It will be primarily a northern hemisphere comet during its brightest phase, but its increasing visibility makes it a thrilling target for all observers with access to clear skies.

November: Comet C/2025 K1 (ATLAS)

Just as Comet Lemmon fades, Comet C/2025 K1 (ATLAS) steps onto the stage. With perihelion on October 8, we’ll be checking in on it post-perihelion in November to see if it survived its close brush with the Sun. If this comet does survive, it’s expected to make its closest approach to Earth on November 26.

This makes November both a scientific and suspenseful month: your observations will help answer the question, “Did the comet survive perihelion?”

A Season to Remember

Taken together, this sequence gives us three comets in a row:

• September: 3I/ATLAS before it disappears
• October: C/2025 A6 (Lemmon) at its brightest
• November: C/2025 K1 (ATLAS) for a post-perihelion check

For northern observers, this really is an autumn of comets, with back-to-back opportunities to observe these ethereal objects from deep space. But our southern hemisphere friends needn’t feel left out: November brings 3I/ATLAS back in their favor, and the global Unistellar community ensures that every observer’s contribution matters.

Stay tuned as we share images, light curves, and stories from across the network. With three comets on the calendar, this season is shaping up to be one of the most exciting periods for comet hunters in recent memory.

You can learn more about each of these missions on our Cometary Activity Missions page, and review how to make science observations with our Tutorial. Clear skies!

This article was originally published at science.unistellar.com