Comet C/2025 A6 (Lemmon): A stellar visitor in October

In the immensity of the universe, occasionally an unexpected visitor appears and captures everyone's attention: a comet. This October 2025, the sky gives us Comet C/2025 A6 (Lemmon), a traveler from the far reaches of the solar system that promises to be one of the most fascinating astronomical events of the year.

Discovered in early 2025, this comet has not only defied initial brightness predictions, but could be visible to the naked eye under dark skies.

A Surprising Find

Imagine a faint, fuzzy dot in the sky, mistaken at first for a nondescript asteroid. This is how the story of Comet Lemmon began.

On January 3, 2025, the Mount Lemmon Survey telescope in Arizona (USA) captured images of an object with an apparent magnitude of just 21.5, so faint that it was 600,000 times dimmer than the brightest star in the night sky, 4.5 astronomical units (AU) from the Sun.

Named after the observatory that discovered it, C/2025 A6 (Lemmon) revealed its true identity shortly after: it showed comet activity with a faint gas coma and an incipient tail.

Its origin is as fascinating as its appearance. This is a long-period comet, with an orbit of approximately 1,350 years, from the enigmatic Oort Cloud: a spherical envelope of ice and dust that surrounds our solar system like a distant shield.

From Darkness to Spectacle

Initially, astronomers estimated that Lemmon would reach a maximum magnitude of 10, too faint to be seen without instruments. But, as often happens with these unpredictable travelers, reality exceeded expectations.

The most recent observations indicate that it will reach a magnitude between 3.5 and 4.4, bright enough to be seen with the naked eye from dark skies. A true cosmic script twist.

Key Dates and Moments of Observation

Here's a guide so you don't miss the best of the show:

Highlights

July 2 – Solar conjunction (invisible from Earth).

October 10 – Visible in the constellation Ursa Major, with magnitude ~5.9 and an ionic tail of up to 3°.

October 16 – It will pass less than 1° from Cor Caroli, in Canes Venatici.

October 21 – Closest approach to Earth: at 0.60 AU (90 million km). It coincides with dark skies due to the New Moon.

November 2 – Crosses the celestial equator, also making it visible from the southern hemisphere.

November 8 – Perihelion (maximum proximity to the Sun, at 0.53 AU). Maximum expected brightness.

How to See Comet Lemmon?

You don't need a telescope to observe, but following these steps will help you enjoy it to the fullest:

When to look for it

Until mid-October: best in the morning sky (4–5 a.m.).

After October 15: visible after sunset (7–8 p.m.).

Best nights: October 20 to 23, without Moon and with the peak of the Orionid meteor shower.

Where to look

Look for dark skies, away from light pollution.

From high latitudes in the northern hemisphere, the comet is already circumpolar (visible all night).

Use apps like Stellarium to locate it.

What to use

At the naked eye: if it reaches magnitude 4 or more, you will see it as a diffuse star with a small tail.

7×50 or 10×50 binoculars: reveal details of the coma and its tail.

A Green Comet and Other Cosmic Companions

Comet Lemmon's greenish glow is due to the presence of gases such as carbon dioxide in its coma.

Furthermore, he is not traveling alone. It shares the celestial scene with other comets visible this month, such as C/2025 R2 (SWAN) and C/2025 K1 (ATLAS), making October a “green” month for comet hunters.

A Message from the Origins of the Solar System

Beyond its ephemeral beauty, Comet Lemmon is a time capsule. These icy travelers are primitive remnants of the formation of the solar system, so if you've ever wanted to see a comet without a telescope, this is your chance.

When observing Comet Lemmon and its greenish glow, we realize that we are part of an immense universe, where even something fleeting can surprise us.