Comet Lemmon (C/2025 A6) is rapidly brightening because it attracts nearer to each the solar and Earth, evolving right into a putting object already seen via small telescopes and binoculars and shortly, fairly probably, to the bare eye.
The icy customer, found on Jan. 3 by the Mount Lemmon Survey in Arizona, is the brightest comet to look in our sky since Comet C/2024 G3 (ATLAS) last January. It will swing close to the sun, a point called perihelion, on Nov. 8, passing about 49.25 million miles (79.25 million kilometers) from our star.
Now, as it brightens rapidly in the predawn sky, skywatchers around the world are preparing for its best and possibly brightest display in late October.
What to expect
Typically, during a given year, several comets will appear that come within range of good binoculars or small telescopes. But a comet bright enough to be readily visible to the unaided eye comes along usually only once or twice per decade.
According to the most optimistic forecasts, at its brightest later this month, comet Lemmon is projected to possibly approach +3 magnitude (such a brightness is comparable to the star Megrez, the star within the Big Dipper that joins the deal with with the bowl). So, these upcoming weeks will afford skywatchers an uncommon alternative.
Of course, a comet’s look is way totally different and fewer nicely outlined than the sharp picture offered by a star. In August 1974, Kenneth Weaver, an assistant editor of National Geographic journal, offered a wonderful description of a comet considerably corresponding to Lemmon. Weaver had traveled to the darkish skies of Kitt Peak National Observatory close to Tucson, Arizona, for a glimpse of Comet Kohoutek. He wrote:
“No spectacular lighting of the sky, no radiant display; One moment it was not there, the next moment it appeared. To the naked eye, it seemed as though a giant paintbrush, dipped in whitewash, had been drawn swiftly across the black wall of heaven, leaving a ghostly swath above a gently glowing blob.”
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But when Mr. Weaver wrote these phrases greater than half a century in the past, he was describing a modestly shiny comet from a location fully freed from gentle air pollution. Today, with the glare of shiny lights seemingly metastasizing in all places, it’s far harder to seek out such darkish, starry and pristine circumstances. Urban skyglow has robbed many people of our evening skies and the overwhelming majority of the inhabitants of the United States now lives in areas the place the celebrities are largely blotted out by extreme lighting.
If you reside in a shiny metropolis or suburban space, your greatest probability to see Comet Lemmon will probably be to move to a dark-sky web site removed from streetlights. Look for a spot the place the Milky Way is seen overhead — an indication of actually darkish circumstances. Under hazy, light-polluted skies, the comet could seem faint or under no circumstances.
Related: Astrophotographers seize dazzling new views of Comet C/2025 A6 (Lemmon) because it brightens for October skies
Comet metamorphosis
Comet Lemmon has confirmed to be a very energetic comet, with noticeable modifications occurring nearly from evening to nighttime. As it races towards the interior solar system, the comet will continue to brighten through October while gradually expanding in size.
Its closest approach to Earth (perigee) comes on Oct. 21, when it will pass about 55.4 million miles (89.2 million km) from our planet.
Predicting what a comet will look like, however, is notoriously tricky. Its brightness, color, and tail shape depend on several factors: its orbit, its angle relative to Earth and the sun, and the makeup of its icy nucleus. Each comet’s heart is a clump of ancient solar system debris — a mix of dust, rock, and frozen gases, much like the particles that make up Saturn’s rings.
As sunlight heats that nucleus, the ice vaporizes, releasing jets of gas and dust that form the comet’s signature tail. In Comet Lemmon’s case, early images show that its tail is made mostly of gas, giving it a faint bluish hue and a thin, straight appearance pointing directly away from the sun.
On the other hand, comets that are prodigious producers of dust, are the ones that are eye-catching because such dust tails appear much brighter. The dust tail is a flat sheet of material spread out in the plane of the comet’s orbit with one edge immediately adjacent to the gas tail.
Many happy (comet) campers
To date, most of the reviews coming in concerning the comet’s appearance have been very favorable.
Despite bright moonlight from October’s full Supermoon, recent comet brightness estimates at the Comet Observation Database (COBS) point out that Lemmon has been a comparatively simple object to sight with good binoculars. As of Oct. 6, a consensus of the comet’s brightness confirmed it hovering close to magnitude +6.1. (The decrease the determine of magnitude, the brighter the article. The brightest stars are magnitude 0 and +1. The threshold of naked-eye visibility below a darkish, moonless sky registers at round +6).
The head or coma measures at round 8 minutes of arc, or roughly one-quarter the obvious measurement of the moon. Visually, the size of the tail is round 1 diploma or twice the width of the moon; long-exposure images, nevertheless, present the faint gasoline tail to be many instances longer.
When and where to look
Currently, comet Lemmon is a morning object. In order to see it, you’ll have to get up before dawn breaks — about 90 minutes before sunrise. The comet is currently passing through the southern boundaries of Ursa Major, the Great Bear. “This comet is developing very nicely and it is already an impressive object, well-placed for observation in the morning sky,” Nick James, director of the Comet Section of the British Astronomical Association, told Spaceweather.com. “It is definitely worth getting up for!”
The full moon on Oct. 6 made recognizing faint objects tough, however visibility will enhance because the moon wanes. After final quarter on Oct. 13, the moon turns into a slim crescent, permitting a lot darker skies for comet viewing.
Thursday morning, Oct. 16, will present a fantastic alternative to find comet Lemmon due to its proximity to a conspicuous star. That star is Cor Caroli, the brightest star within the constellation of Canes Venatici, the Hunting Dogs. Cor Caroli shines at magnitude +2.8 and on Oct. 16, the comet will probably be located simply 1° (two moon widths) above that star. Ninety minutes earlier than dawn, search for the Big Dipper, which can seem like standing upright on its deal with within the northeast sky.
Now draw an imaginary line diagonally via the Dipper’s bowl from Dubhe (the higher proper star within the bowl) down via Phecda (the decrease left star within the bowl) and lengthen that line downward about twice the space between these two stars and that may carry you to the neighborhood of Cor Caroli. Aim your binoculars towards this star and Comet Lemmon will probably be located simply above.
Transition to the night sky
Oct. 16 can also be the date when the comet will turn out to be obtainable to night skywatchers. In reality, Lemmon will seemingly placed on its greatest present between Oct. 22 and Oct. 28, low within the west-northwest sky proper after the top of night twilight. During that timeframe, the comet will probably be monitoring quickly via the constellation Boötes the Herdsman and into Serpens the Serpent on Oct. 24. Around the end of twilight, it will sit about 15° above the horizon, roughly one and a half fist-widths at arm’s length.
On the evening of Oct. 22, the comet will lie about 2° left of the star Izar (Pulcherrima), a beautiful double star with a yellow-and-blue color contrast often described as golden and sea green.
Oct. 22 through Oct. 28, will also be when the moon will not be much of a factor, being no worse than a waxing crescent phase. This will also be the time when comet Lemmon is expected to shine at its brightest.
Japanese comet expert Seiichi Yoshida thinks the comet will peak at round +4 magnitude, however Dutch comet professional Gideon Van Buitenen has lately revised his brightness forecast, indicating that the comet would possibly get as shiny as magnitude +3.3, which might make it evident with the bare eye in opposition to a darkish sky. “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,” provides James.
Final ideas
Those blessed with very darkish skies would possibly even be capable to proceed following with simply their unaided eyes till the primary week of November. Of course, the comet might all the time dim rather more quickly, or a sudden, sudden flare-up might additionally happen. But these are excessive circumstances. So far, the comet has carried out very nicely and there’s no cause to not consider that it’s going to proceed to thrill Northern Hemisphere observers for a number of extra weeks.
Once once more, we must always stress that the darker your observing web site, the higher the comet will seem. With the intense moon just about out of the best way through the second and third weeks of April, potential comet observers are prone to have their biggest success.
Good luck and clear skies!
For extra data on how one can {photograph} and comets for your self, try our comet skywatching guide.
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, Sky and Telescope and different publications.
Editor’s Note: If you wish to share your photographs of Comet Lemmon (C/2025 A6) with Space.com’s readers, then please ship your photograph(s), feedback, and your identify and placement to spacephotos@house.com.