David Bridges
Highlights
- Comet Lemmon (C/2025 A6) is set to be at its brightest on October 21.
- This comet was discovered by the Mount Lemmon Survey in January 2025.
- Lemmon will be visible without the need for a telescope or binoculars.
- The comet’s closest approach to Earth will be about 56 million miles away.
This year is a boom time for comets. Not only did we have the interstellar object 3I/ATLAS gracing our skies (and Mars’) earlier this year, but now we have another brand new comet to look out for.
Expected to be at its brightest on October 21, this month you might have the chance to spot the comet Lemmon (C/2025 A6) blazing across the night sky—no telescope or binoculars required.
Lemmon was first discovered in January this year by the Mount Lemmon Survey in Arizona. As amateur astronomers may be aware, several comets will pass the detection range of binoculars or telescopes in any given year. But it’s rare that a comet will shine bright enough to be spotted with the naked eye. October 21 also happens to be a date of the new moon, meaning the sky will be otherwise dark and primed for the comet to zip by.
“This comet is developing very nicely and it is already an impressive object, well-placed for observation in the morning sky,” Nick James of the British Astronomical Association told Spaceweather.com. “It is definitely worth getting up for!”
What is the anatomy of a comet?
Comets, simply put, are “cosmic snowballs,” orbs of icy material that orbit the Sun. Predicting their appearance and trajectory is no easy task, but Lemmon’s unusually bright, active tail has allowed both professional and casual observers to characterize its likely path through the solar system.
At its closest approach to Earth, Lemmon will be about 56 million miles (90 million kilometers) away. Lemmon’s current orbital period is approximately 1,350 years, which will be reduced to about 1,150 years after passing by the Sun’s gravitational field in November. That is, if you miss the comet this year, you’ll have to wait until at least 3175 to see it again.
How can you spot Lemmon?
As of now, Lemmon is visible only in the morning, although the comet’s trajectory will progressively allow observers to spot it in the evenings. Last month, it passed by the Gemini constellation, traveling through the skies until it entered Ursa Major earlier this month.
Again, comet luminosity can be touch-and-go, so it may well grow dimmer than expected. But astronomers are reasonably confident about their current predictions. “
So far, the comet has performed very well and there is no reason not to believe that it will continue to delight Northern Hemisphere observers for a few more weeks,” according to Space.com.
“I think we can now be reasonably confident that this will be a very nice evening object when it is at its brightest around New Moon in late October,” James said.
Daniel Mercer
