This autumn’s sky will be exceptionally generous for fans of space phenomena. In fact, a double show is coming, with the passage of two comets, one bright enough to be seen with the naked eye. Their names are: C/2025 A6 Lemmon, the true prima donna, and C/2025 R2 Swan.
Comets Lemon and Swan are arriving: when and how to see them
After having enchanted us for weeks in the last hours of the night, showing itself just before dawn to the telescopes and lenses of astronomers and photographers, comet C/2025 A6 Lemmon is ready to give its best, now in the evening sky, immediately after sunset, a condition that should favor even the laziest. Discovered last January 3 as part of the near-Earth asteroid search program conducted by the Mount Lemmon Observatory in Arizona, USA (survey from which the star evidently took its name), the comet has given rise to a real crescendo and since September it has literally started to put on a show, developing a long tail, very rich in details.
There are two important dates to mark on the calendar: Tuesday 21 October and Saturday 8 November. In the first, C/2025 A6 Lemmon will be at the minimum distance from Earth, around 90 million kilometres: the comet will be close to its maximum brightness, expected for the last week of October. On those days, the star should become better visible to the naked eye (it already is now, but we are at the limit), observing from dark places at about 15 degrees above sea level towards the west, around 8pm (which will become 7pm from 26 October, when we return to solar time). In any case, modest binoculars will be enough to see it as it passes between the constellations of Bootes, Serpens Caput and Ophiucus. The Moon (new on the 21st) will begin to impact observations from the beginning of November, therefore the evenings between 20 and 31 October will be the best to attempt observation.
On November 8, however, the comet will reach perihelion, or the minimum distance from the Sun, 79 million kilometers from our star, a real turning point along its considerably eccentric orbit. From that date onwards, the vision from our latitudes can be considered concluded. Incredibly, Lemmon is not the only interesting comet visible these days: with binoculars it is in fact possible to observe comet C/2025 R2 Swan, discovered on September 9 (through the Swan instrument on board the SOHO orbiting solar observatory, hence the name) and passed to perihelion three days later. At the moment, it is just below the threshold of theoretical visibility to the naked eye and is slowly, inexorably weakening.
Swan will be at its closest distance from Earth, about 39 million kilometers, on October 20, just one day before the other: a nice coincidence. As astrophysicist Gianluca Masi, founder and head of the Virtual Telescope Project, explains, “to observe the C/2025 R2 you need binoculars, aiming – at the same times indicated for the Lemmon – between the south-west and the south, at a height between 25 and 45 degrees, from today to the end of the month, while it will parade through the constellations of Ophiucus, Sagittarius, Eagle and Aquarius”. The Virtual Telescope Project will show both comets live on October 20th, starting at 7.30 pm: to participate, simply access the following link.
