This fall, the comet C/2025 A6 (Lemmon) It is becoming visible at dusk from much of the Iberian Peninsula, with a brightness that can be perceived without instruments under favorable conditions. If you have a dark sky, away from streetlights and buildings, is a perfect goal for a short getaway to the countryside.
The most suitable stretch to observe it in our latitudes is concentrated between mid-October and mid-November, with a few particularly welcome nights at the end of the month. Anyone looking to plan their getaway in advance should take note the weekend of the 25th and 26th and the nearby days: this is when the comet will appear higher at sunset and with greater contrast.
What we know about comet C/2025 A6 (Lemmon)
The object was detected by the Mount Lemmon Survey on January 3, 2025, and after reviewing previous Pan-STARRS images from November 2024, it became clear that it was a comet. The first measurements showed a compact comma and an incipient tail, confirming its nature.
Its orbit is strongly inclined, about 143,7° with respect to the plane of the planets, which implies a retrograde motion. This favors observers in the northern hemisphere, since during this appearance the comet gains altitude toward northern latitudes.
In April, the Lemmon passed relatively close to Jupiter (≈348,5 million km). That gravitational interaction reduced its orbital period by about two centuries: from an estimated value of ~1.350 years to approximately 1.154 years nowadays.
The key dates of this step are two: the closest approach to Earth, on October 21, at around 0,60 AU (~90 million km), as well as the perihelion on November 8, about 0,53 AU from the Sun. During this interval, the comet develops its characteristic greenish hue and unfolds tails of ionic gas and dust.
When and where to see it in Spain
From the peninsula, the comet is observed in the evening sky between October 18 and around November 12, with its best side between the October 25 and 28The expected brightness is around magnitude 4: at first glance it requires dark skies, but with binoculars it is easily appreciated.
On those days, it is advisable to look after sunset, when the sun is over. civil twilightFor example, in Madrid on October 27 it appears around 18: 45 CET at an approximate height of 41° over the west-southwest sector and slowly descends until it sets around the 22: 10 CETIn other areas of Spain the figures vary very little.
As the season progresses, the comet will lose altitude: for the November 10th Its maximum elevation can be around 26° above the western horizon. If a night is complicated by clouds or haze, try again on a nearby date: visibility varies little from one day to the next.
In the star map, at the end of October it transits through Bootes (The Cowherd), and at the beginning of November it moves towards OphiuchusThe practical reference is simple: look for the Big Dipper, follow the arc towards the bright Arcturus and explore the area to the west/southwest shortly after twilight; for more information on dates and how to watch it.
- October 21: Moonless night and closest approach to Earth; very favorable conditions.
- October 25–28: ideal balance between height and apparent brightness at dusk.
- November 5th: Full moon (on the opposite side of the sky, with less effect).
- November 8th: perihelion; the comet is already low over the evening horizon.
Observation and photography tips
For comfortable observation, choose a place with clear west/southwest horizon and minimal light pollution. Let your eyes adapt to the darkness at least 30 minutes And if you carry a flashlight, use a red light to maintain sensitivity.
At first glance the comet appears as a diffuse stain; with 7-12x binoculars the nucleus and a short tail pointing away from the Sun. A light tripod helps a lot to stabilize the image.
If you want to photograph it with your mobile, place the phone on a tripod and activate Night or Astrophoto mode. As a guide, try ISO 1600--3200 and exhibitions of 5–10 seconds; raises or lowers the values depending on the darkness of the sky.
With camera and tripod, for a wide frame use lenses of 14--35mm af/2–f/2.8, ISO 1600–3200 and shutter speeds 10–20 secTo get a little closer to the comet, an 85–135 mm lens can work well. 5–10 sec exposure to avoid star trails.
Note that comets move against the stellar background. If you stack images, align one version with the stars and another with the comet to keep both sharp. Celestial mapping apps can help you locate it accurately in your local sky.
Anyone observing from Europe will find conditions similar to those on the peninsula: better at dusk, low in the west and with a brightness suitable for binoculars. In parallel, it may coincide in dates with another faint visitor, C/2025 R2 (SWAN), but the evening protagonist in our latitudes it is Lemmon.
With an observation window that fits with moonless nights and a glow around magnitude 4The passage of Comet Lemmon offers a wonderful opportunity to get started or revisit the sky. Just choose a good spot, look west after sunset, and let patience do the rest: The best nights fall at the end of October and the show is worth the try.
