Observing the October 2025 Comets
06 Oct. 2025
As the year draws to a close, several comets are passing through the inner Solar System. Predicting their visibility can be tricky, a comet’s encounter with the Sun can dramatically affect its brightness, and promising newcomers sometimes break apart before putting on the expected show.
That said, October 2025 is shaping up to be a great month for comet watchers. One comet, C/2025 A6 (Lemmon), is already well visible and steadily brightening. Another has safely passed perihelion and will be observable in the second half of the month.
This guide covers everything you need to know to enjoy October’s comets and observe them with your Vaonis smart telescope.
Comet C/2025 A6 (Lemmon) captured by Nathanael Martin with Vespera II
(from Vaonis official Facebook user group)
Update - October 20
With both comets making their closest approach to Earth and the New Moon providing dark skies, we’ve now entered the best period to observe comets C/2025 A6 (Lemmon) and C/2025 R2 (SWAN).
Comet A6 (Lemmon)
Currently shining at magnitude 4.7, its coma is visible to the naked eye from dark-sky locations.
The tail isn’t visible without optical aid but can easily appear in simple photos.
With Vespera, the comet and its tail are clearly visible, revealing many detail.
Best time to observe: Just after sunset. The farther north you are located, the better the visibility.
Comet R2 (SWAN)
Though not visible to the naked eye, this comet is bright enough to be easily observed with Vespera. Its tail is much fainter than that of A6 (Lemmon) and may be challenging to bring out clearly.
Best time to observe: In the evening, from low latitudes, between the constellations Scutum (the Shield), Sagittarius, and Capricornus.
Observation Tips
For A6 (Lemmon), initialize Vespera as soon as the first bright stars appear, then create a manual target using the comet’s coordinates.
Refer to the information below and to the Ultimate Vespera Guidebook to learn more about comet observation.
Capture Parameters
A6 (Lemmon): Since it’s particularly bright, try 5-second exposures to avoid overexposing the coma.
R2 (SWAN): Being fainter, 10-second exposures are recommended.
Gain: Set to 20 for both comets.
Stacking duration: As both comets move quickly across the sky, avoid stacking for more than a couple of minutes to prevent the comet’s core from appearing elongated.
What are comets?
A comet is a small icy body orbiting the Sun that becomes spectacular when it enters the inner Solar System. Made of rock, dust, and frozen gases, a comet remains faint and inactive far from the Sun. As it approaches, solar heat causes the ice to sublimate, forming a coma, a glowing cloud of gas and dust, and often a long tail that streams away from the Sun under the influence of the solar wind.
Comets are ancient leftovers from the Solar System’s formation, preserving pristine material from its earliest days.
Why comets are fascinating to observe
Unlike galaxies or nebulae, comets are dynamic and constantly evolving. Their brightness, shape, and tails can change from night to night. Each apparition is unique: some comets grow long, elegant gas tails; others show broad dust fans or striking green comas. Many are once-in-a-lifetime visitors, making each bright comet a rare celestial event.
For imagers, comets are a rewarding challenge, capturing a moving object against the fixed star field, while visual observers enjoy the excitement of following a traveler passing through our Solar System in real time.
The Main features of a comet
Nucleus (core)
A small, solid body of ice, rock, and dust, often just a few kilometers wide, usually hidden inside the bright coma.
Coma
A large, glowing halo of gas and dust formed when sunlight heats the nucleus and causes ices to sublimate. Often greenish due to carbon compounds; can reach tens of thousands of kilometers in size.
Dust tail
A wide, often curved tail made of tiny particles pushed away by sunlight. Usually yellowish-white.
Ion (gas) tail
A straight, bluish tail formed by ionized gases blown directly away from the Sun by the solar wind. Always points away from the Sun.
Antitail (rare): A short tail that appears to point toward the Sun, an optical effect when Earth crosses the comet’s orbital plane.
Comet C/2025 A6 (Lemmon) — the star of october
This comet has turned into a pleasant surprise. When it was discovered in January, no one expected it to become so striking. It has already reached magnitude 6 and continues to brighten as it approaches Earth. It’s perfectly suited for observation with Vespera and may soon even become visible to the naked eye.
Early october
From the Northern Hemisphere, the comet is visible in the morning sky before sunrise, low on the northeastern horizon in Ursa Major.
Its tail is already well formed and changes appearance from night to night.
Easily observable with Vespera, though it will gradually sink lower toward the horizon by mid-October.
Mid-october
The comet transitions from a morning object to an evening object as it moves across the sky. Around October 15, it will be in Canes Venatici and can be observed both at dawn and dusk.
However, evening observations may be affected by twilight, delaying the time you can initialize Vespera.
October 20–25, best period
The comet makes its closest approach to Earth on October 21, when it should reach peak brightness and could become visible to the naked eye. This coincides with the New Moon, ensuring dark skies.
It will be visible in the evening after sunset, low in the western sky, moving from Boötes toward Serpens.
Comet Tsuchinshan-ATLAS caprured by Vespera Pro in 2024.
A6 Lemmon might become as bright.
Late October
The comet sinks lower toward the horizon and gradually fades as it moves away from Earth and the Sun.
Comet C/2025 R2 (SWAN)
Discovered recently (September 11), this comet is currently better placed for the Southern Hemisphere, but its visibility will improve for northern observers later this month.It safely passed perihelion on September 12, so it is unlikely to break apart.
Comet C/2025 R2 (Swan) during its close approach with the Eagle Nebula, captured by Nathanael Martin with Vespera II
(from Vaonis official Facebook user group)
First Half of October
Around magnitude 6.5, C/2025 R2 is visible in the evening sky above the western horizon, between Scorpius and Libra, from the Southern Hemisphere.
Second Half of October
By mid-October, the comet becomes observable from the Northern Hemisphere, entering Serpens. Its closest approach to Earth is on October 20, and with the New Moon on October 21, conditions will be excellent.
The comet is expected to remain around magnitude 6–7, making it easy to capture with a Vaonis smart telescope.Observe it as soon as possible after sunset, once your instrument can be initialized.
Toward the end of the month, it will climb higher in the sky, passing through Scutum, Aquila, and Aquarius, though it will slowly fade in brightness.
How to Observe Comets with Vaonis Smart Telescopes
Comets are moving targets, their position changes constantly as they travel through the Solar System.
Because of this, they are not included in Singularity’s object catalog, but you can easily observe them by creating a manual target.
1️⃣ Get the Comet’s Coordinates
You’ll need the Right Ascension (RA) and Declination (Dec) for the time of your observation.
These values change regularly, so always check them just before you observe.
You can use a planetarium app or sky software such as Stellarium to find accurate coordinates.
2️⃣ Create a Manual Target
For detailed instructions, refer to the Vespera Guidebook (page 62).
Select “Nebula” as the object type.
Set an exposure time appropriate to the comet’s brightness.
Use the coordinates to create your manual target in Singularity app
3️⃣ Start the Observation
Initialize Vespera and launch the session from your newly created manual target.
Choosing the Right Exposure Time and gain
If the comet is visible to the naked eye: try 1–5 seconds per frame.
If the comet is faint: start with 10 seconds per frame and adjust if needed.
Experiment until you find the best balance between signal and motion blur.
Since it’s a high-contrast object (the coma is much brighter than the tail), it may be useful to reduce the sensor gain below the default value — for example, to 10 or even lower. Experiment to find what works best.
How Long to Capture
Comets move relative to the background stars, sometimes quickly, especially near close approach.
Vespera tracks the stars, not the comet itself, so if you stack for too long, the comet’s core will start to stretch into a line. For this reason, it’s best to limit individual live-stack sessions to just a few minutes.
For longer capture, you'd better save the FITS files then stack them with a dedicated software that will align on the comet rather than on the stars.
Framing the Comet
With a long, extended tail, a comet can become a very large target. Astronomy software will usually provide the coordinates of the comet’s nucleus, but you may want to adjust your framing — for example, placing the nucleus near the edge of the image to capture a larger portion of the tail.
Use Singularity’s Reframe feature to fine-tune the composition and get the framing you want. Alternatively, you can use the coordinates of another point, such as a star located along the tail, to center that area in your field of view.
Scheduling a Comet Observation
You can use Plan My Night to schedule an automatic observation of a comet, for example, when it is a morning target.
When doing so, make sure to create your manual target using the comet’s coordinates for the time of the planned observation, not the moment when you create the target.
Going Further: Manual Stacking
For the highest-quality images, you can enable FITS frame recording and later process the data manually using software that aligns on the comet’s nucleus rather than the stars (e.g., PixInsight, Siril, or Astro Pixel Processor).
This technique allows you to combine long exposures without smearing the comet’s core.
