Comet Lemmon (C/2025 A6) may soon make a play for the title of “comet of the year” for Northern Hemisphere observers. Discovered in January 2025 and initially thought to be an asteroid, it’s now forecast to be easily visible in binoculars, and possibly to the naked eye, during mid-October. Comet Lemmon will make its closest approach to Earth on Oct. 20–21, coinciding with the dark skies of a new moon and the peak of the Orionid meteor shower. October is also a great month for displays of the Northern Lights, making it a potentially exciting month for skywatchers.
C/2025 A6 (Lemmon) was discovered on Jan. 3, 2025, by the Mount Lemmon Survey in Arizona. Initially mistaken for an asteroid at magnitude +21.5, it was later found in an image from Nov. 2024.
Comet Lemmon is a long-period comet that visits the inner solar system around every 1,350 years. Comets are made of ice, dust and rock — leftovers from the creation of the solar system.
The comet will make its closest pass of Earth on Oct. 20-21, and reach perihelion — its closest point to the sun — on Nov. 8.
How bright it will get remains to be seen, with estimates ranging from magnitude +4.5 to +7. At the brighter end, it could be faintly visible to the naked eye under rural skies, though it’s more likely a pair of binoculars will be required. Forecasting the brightness of a comet is notoriously difficult.
Comet Lemmon will largely be visible from the Northern Hemisphere. A pre-dawn object in early October, it will be seen in both morning and evening skies by mid-October. It will then fade by mid-November as it exits the inner solar system.
The best nights to see Comet Lemmon will be Oct. 20-23, when it is both closest to Earth during dark, moon-free nights around new moon. However, surely the highlight will come on Oct. 20-21 when its closest approach coincides with the peak of a meteor shower. If there’s geomagnetic activity and aurora, it could be something very special. However, aurora displays depend on solar activity and are never guaranteed.
In April 2025, Comet Lemmon passed about 216 million miles (348 million km) from Jupiter. According to Space.com, Jupiter drained some of Lemmon’s orbital energy, shortening its period by nearly 200 years. Instead of returning every 1,350 years, it will now loop back in about 1,150 years. It will return in the year 3175.
The last bright comet seen widely without binoculars was C/2020 F3 (NEOWISE) in July 2020. Visible during the COVID-19 pandemic, it was the brightest Northern Hemisphere comet in decades, according to NASA. NEOWISE won’t return for about 6,800 years.