Last chance to spot Comet Lemmon for over a thousand years is here!
This comet is best seen through a telescope or binoculars, but it may be visible to the unaided eye for the next two weeks!
Look to the west after sunset, starting near the bright star Arcturus, and you may spot a comet visiting us from the edges of our solar system.
The big news in space over the past few months has been about the alien comet flying through our region of space, but there's another comet up there that is much closer to Earth right now, and a lot easier to see.
Comet C/2025 A6 Lemmon was discovered in the first few days of this year, as it showed up in observations taken by the Mount Lemmon Observatory. While it was dim enough that only the largest observatories could see it through most of the year, once it passed around the Sun in July, it became bright enough to spot with backyard telescopes.
This week, the comet reaches its brightest in our skies, at a magnitude of around 4, or possibly even better. While the human eye can typically see down to a magnitude of 6.5 from the darkest places on Earth, at a magnitude of 4 or better, those of us living in rural or even suburban areas have a chance to spot it.
Comet A6 Lemmon's position relative to the western sky, every 3rd night starting on October 20, 2025, at 7:40 p.m. local time. The position of West in this image stays fixed for all frames, showing how the comet's position shifts from the northwest to the west and southwest throughout the last week of October and first week of November. (Stellarium/Scott Sutherland)
When looking for Comet Lemmon, the bright evening star Arcturus acts as a convenient guide, at least to start. Spot it up and to the north of Arcturus on October 20, to the south of Arcturus by the 23rd, due west by the 29th, and then swinging through the southwest sky through the end of October and first week of November.
It may be difficult to spot the comet without some kind of assistance. A cellphone camera set to "Night Mode" or the equivalent, can help a lot in locating it. Point your camera at the western sky, hold it steady (or prop it up on something solid), and let the camera take a long-exposure picture. Then, scan through the picture to see if you can find it, and use that to spot it in the sky.
Using a pair of binoculars or a telescope to spy the comet is even better. The camera trick can still be used to locate it, first, then use the binoculars or telescope for a better view.
As we get farther into November, the comet will become dimmer and harder to spot, although it should still be visible via telescope for some time.
One and only chance...
Similar to Comet Halley, Lemmon is on a retrograde orbit, which means that it travels around the Sun in the opposite direction that the planets (including Earth) orbit.
However, unlike Halley, C/2025 A6 Lemmon is on a very long orbit.
A solar system simulation shows the positions and orbits of the outer planets, with the orbits of Comet Halley and Comet Lemmon overlaid. Lemmon's orbit extends FAR off the left side of the image. (NASA/JPL-Caltech/Scott Sutherland)
Halley takes 76 years to go around the Sun once, and reaches just outside the orbit of Neptune, about 35 astronomical units (4.5 billion kilometers) at its farthest distance from the Sun.
In contrast, Lemmon apparently originated from over three times farther away, at around 120 au out, and before it swung around the Sun, its orbital period was calculated to be once every 1,350 years.
Due to the speed it picked up at perihelion (its closest distance to the Sun), it is now on a slightly shorter orbit, which will take it out to about 110 au, and bring it back this way in about 1,150 years.
Either way, we are not going to see this comet again for a very, very long time. So, this will be our last chance to check it out!
(Thumbnail image shows Comet C/2025 A6 Lemmon as it appeared on October 2, 2025, captured by Dimitrios Katevainis from eastern Crete. The image is shared under the CC BY-SA 4.0 Creative Commons license)