The thousand-year journey of comet C/2025 A6 (Lemmon) towards the inner planets of the Solar System enters its most critical point. Eleven months after its discovery in early 2025 at the Mount Lemmon Observatory in Arizona (United States), the comet has attracted the attention of the scientific community and amateur astronomers for the gradual increase in its brightness as it approaches perihelion, the point of its orbit closest to the Sun, which will occur on November 8.
Although images captured with professional cameras already show the development of a long tail of green tones, the most recent calculations estimate that Comet Lemmon will reach its maximum brightness during the last nights of October and the first of November, when it will be possible to observe it with the naked eye even in very dark skies. “The feeling is that it is a little brighter than expected at the beginning of the year, when it was not believed that it would be possible to detect it with common means such as binoculars, but now it can be observed with relative ease”, explains to EL PAÍS René Ortega Minakata, astrophysicist in charge of the scientific communication team of the Institute of Radio Astronomy and Astrophysics (IRyA) of the UNAM.
A distant visitor
Comet Lemmon’s elongated orbit extends to the Oort Cloud, a region that surrounds and defines the limits of the Solar System and concentrates billions of icy bodies, remnants of the formation of our cosmic neighborhood. According to current estimates, the aphelion, the farthest point from the Sun in its orbit, is about 36,000 million kilometers away, so its orbital period is calculated to be about 1,350 years. Unlike periodic comets, which reappear among the inner planets of the Solar System with a frequency of less than 200 years, Lemmon is a non-periodic comet, that is, a very distant visitor whose orbit may pass only once between the hot, rocky worlds of the Solar System. “The difference with comets like Halley is that they do not return to the inner Solar System, or at least they do not do so for many thousands of years. What we can say for sure is that it is the first time it has entered the inner Solar System and it will most likely be the last time,” explains Ortega Minakata.
The name given to each comet is based on a naming system established by the International Astronomical Union and reveals details about its nature: in the case of C/2025 A6 (Lemmon), the prefix “C” reveals that it is a non-periodic comet. While 2025 represents the year in which it was discovered, at the next level, the combination A6 specifies in which fortnight of the year it was identified and the order it occupies among the comets found in the same period: the letter “A” corresponds to the first fortnight of January, while the 6 reveals that it was the sixth comet discovered in the first fortnight of January 2025. Lemmon, finally, is a direct reference to the site where it was discovered, Mount Lemmon. Observatory in Arizona (United States).
How and when to see comet C/2025 A6 (Lemmon) from Mexico?
The best time to observe Comet Lemmon’s passage through the inner worlds of the Solar System will be in a window of a few days between late October and early November, just before perihelion, the point in its orbit closest to the Sun, which will occur on November 8. “That’s when it’s expected to be brightest, because that’s the combination of when it’s closest to the Earth and the Sun,” explains Ortega Minakata.
To observe it from central Mexico it is necessary to find a place free of light pollution and direct your gaze after sunset towards the west, where the sun sets. The comet will maintain a descending trajectory as night falls, so the opportunity to see it will occur between 7 p.m. and 8.30pm, before it disappears over the horizon. “On the one hand, you need a very dark sky, with as few artificial lights as possible; and also that it has a good horizon, i.e. that there are no objects, buildings, trees or hills right in the direction in which the Sun sets. Without these conditions it will take a lot of work to find it,” says the astrophysicist. To find its exact location in the night sky, some free star charts like Stellarium have already loaded the comet’s trajectory into their database. Other mobile applications such as SkySafari or Sky Tonight offer augmented reality to point the camera at the sky and orient yourself in the sky more easily.
