How to See Comet Lemmon This October

It was early January 2025 when a faint spot of light was observed at the Mount Lemon Observatory in Arizona. Follow-up observations revealed that the object was a comet from the outer reaches of the Solar System and was named Comet Lemon (C/2025 A6). Its “period” — the time it takes to complete one long orbit of the Sun — is about 1,350 years.

At first, the comet was so faint that it could only be seen with special equipment. But it brightened rapidly as the months passed, and by fall it was bright enough to see through binoculars. It will now become even brighter, as it comes closer to both the Earth and the Sun, and may even be visible to the naked eye.

According to NASAComet will be lemon Closest to Earth around October 21, 2025About 0.60 astronomical units or au (1 au is the distance between the Earth and the Sun). The comet is then predicted to reach its closest point to the Sun on November 8. The comet will probably reach its peak brightness when it reaches perihelion and may be visible to the naked eye if conditions are favorable in a dark sky.

The comet’s tail will also be at its longest extension around the perihelion point. Tails form on comets when solar radiation heats the frozen ice and gases in the comet’s nucleus, causing them to atomize — turning from solid to gas — with the radiation, then some of that material is ejected from the comet in a tail streak. The stronger the radiation, the larger the size of this effect, and so comet tails grow as they approach the star and shrink as they move away.

Comet lemon is notable for its green color. This is caused by the cloud of gas surrounding the comet’s nucleus, known as the “coma”, as diatomic carbon (molecules of two carbon atoms) interact with sunlight to form the color.

Comet Lemon (C/2025 A6) photographed in Slovenia in early October.

Photo: Uros Fink

How to see comets

In early October, Comet Lemon can be found just below the handle of the Big Dipper (or Plough, as it is known in the UK), which is part of the constellation Ursa Major. If you look at the northern sky, you will be able to trace its path. In the Northern Hemisphere, it is predicted To appear in the northwest to western sky after sunset from mid-October. It will remain at a low altitude above the horizon and is expected to emit a faint glow in the twilight just after sunset.

The best time to observe the comet is about a week before and after its closest approach. In November, the comet will cross the celestial equator and be visible from the Southern Hemisphere.

Binoculars or small telescopes are best for observing it, but if you choose a location with little light pollution, you may be able to catch it with the naked eye. If you look at the sky just after sunset when it’s still a bit bright, you might be able to see it. If you’re struggling to find the comet, use a star map app on your smartphone or planetarium software to help you pinpoint its location.