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The most luminous comet in almost 20 years — comet G3 ATLAS (C/2024) — is anticipated to achieve its maximum brightness later this week into early the following week.
The sole inquiry is: “Will you genuinely be able to observe it?”
This astronomical conundrum pertains to Comet 2024 G3 (ATLAS), which was first detected on April 5 of the preceding year by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey, using images captured with a 0.5-meter (19.7-inch) reflector telescope situated in Rio Hurtado, Chile. Upon its discovery, the comet was 407 million miles (655 million km) away from Earth and exhibited an incredibly faint magnitude of +19, which is approximately 158,000 times dimmer than the faintest star that can be seen with the naked eye.
Returning after 160 millennia
An initial orbit for this comet indicated that it would pass remarkably close — fewer than 9 million miles (14 million km) from the sun in mid-January 2025; approximately one-quarter the distance to Mercury, the sun’s nearest planet. However, these preliminary computations also hinted that G3 ATLAS was a new comet arriving directly from the Oort cloud, a vast shell of countless billions of icy bodies surrounding our solar system, located perhaps 10 trillion miles (16 trillion km) from the sun. Minor sun-grazing comets emerging from the Oort Cloud, during their first approach to the sun, typically disintegrate before reaching perihelion (their nearest approach to the sun).
Nevertheless, once G3 ATLAS’s orbit was fine-tuned, it was discovered that it was in fact a dynamically ancient comet, having made at least one prior close approach to the sun, with an orbital cycle of roughly 160,000 years. This raised hopes that — after surviving a previous close encounter with the sun — this comet could endure its forthcoming near pass and potentially provide a brilliant display after the new year begins.
Has favored southern skywatchers
Regrettably, up to this point, the anticipated trajectory of G3 ATLAS has exclusively benefited those in the Southern Hemisphere. Virtually the entire expected pathway of this comet traverses constellations well south of the celestial equator. For observers in the Northern Hemisphere, the comet’s path over the previous month has taken it through the southern constellations of Lupus and Scorpius, currently residing in Sagittarius.
This indicates that for observers situated north of the equator, the comet has been positioned too low on the southeastern horizon and is continuously concealed by the brightness of early morning twilight.
However, as the comet is now nearing its “final stretch” before it swings around the sun, it has started to brighten significantly. For a brief period, its route will veer just far enough north to offer those north of the equator a chance to catch a glimpse of it.
Breakup avoided?
Recent data gathered from the Comet Observation database (COBS) indicate that, on Jan. 2, 2025, G3 ATLAS experienced a sudden increase in brightness, showing nearly a four-fold enhancement in apparent luminosity. Nonetheless, John Bortle, a well-regarded and highly respected comet observer, shared mixed feelings regarding this unexpected brightness surge. In correspondence with Space.com, Bortle remarked:
“The apparent volatility demonstrated in the recent magnitude increase can typically be interpreted as an ominous sign that the comet is exhibiting signs of fragmentation, but some other unusual characteristics reported, such as the ‘shadow of the nucleus,’ is a typical feature of any large comet approaching perihelion, rather than an indication of disruption.”
Still, Bortle remains uncertain about G3 ATLAS’s ultimate destiny, stating, “I believe the odds of its survival are about 50:50,” Bortle mentioned.
Another recognized comet observer, Nick James of the British Astronomical Association, also acknowledged the comet’s most recent surge in brightness. He was recently quoted at Spaceweather.com as stating: “The sudden rise in brightness was noteworthy. This could have been an early indication of disintegration, but since then, the comet is continuing to brighten. It appears this outburst has not been detrimental.”
Another noted comet observer, Nick James of the British Astronomical Association, also commented on the comet’s latest surge in brightness.
“The sudden increase in brightness was noteworthy. This could have been an early indication of disintegration, but since then, the comet is still brightening. It appears as if this outburst has not been detrimental,” Jamesinformed Spaceweather.com.
How luminous will it be?
G3 ATLAS will remain perpetually situated quite close to the sun, prompting the principal inquiry: Will it illuminate sufficiently to be easily perceived against the dusky sky? Sadly, that is challenging to forecast. Just like snowflakes, no two comets are indistinguishable. Astronomers have formulated mathematical models to predict luminosity, yet it is particularly tough for newly discovered or long-period comets like G3 ATLAS, for which historical records of visits are lacking.
On January 4, Daniel Green from the Central Bureau for Astronomical Telegrams in Cambridge, Massachusetts, released an updated bulletin on G3 ATLAS, estimating its brightness based on its development during recent weeks.
The comet is predicted to reach perihelion on January 13 at 10:17 Universal Time (UT), at a distance of 8,695,216 miles (13,993,594 km) from the sun. Later that day, it will come closest to Earth at a total distance of 87.1 million miles (140.1 million km).
Green anticipates the comet might achieve a peak magnitude of -3.2, placing it between the luminosity of Jupiter and Venus, both of which are conspicuous in our evening sky. “The comet will be positioned near the sun when it reaches its maximum brightness, but it’s becoming quite challenging even for observers in the Southern Hemisphere to detect it,” Green communicated to Space.com. “It’s extremely tough to ascertain these comets when they are this close to the sun with regards to visibility.”
Indeed, even though Green’s forecast indicates G3 ATLAS might become considerably radiant, its proximity to the sun raises doubts about whether a casual observer could distinguish it against the brilliant twilight sky. However, if the comet were to intensify in brightness, it may become more observable.
For that to occur, we would need to take forward scattering into account.
Forward scattering: The ‘dusty windshield effect’
Forward scattering in comets refers to a phenomenon that transpires when sunlight is dispersed by dust particles in a comet’s tail and coma, resulting in the comet appearing more luminous. This effect occurs when a comet is positioned between the Earth and the sun, or when the angle between Earth, the comet, and the sun is elevated. Forward scattering can cause a comet to appear substantially brighter, particularly when the phase angle is high. This effect is akin to the experience of driving toward the sun with a dirty windshield.
Forward scattering in comets takes place as sunlight is scattered by dust particles in a comet’s tail and coma, making the comet appear brighter. This occurrence happens when a comet lies between the Earth and the sun, or when the angle between the Earth-comet-sun is significant. Forward scattering can greatly augment a comet’s brightness, especially when the phase angle (the angle between Earth, the comet, and the sun) is considerable. It is similar to the sensation of driving toward the sun with a dusty windshield.
In the instance of G3 ATLAS, its phase angle is expected to peak at 115 degrees late on January 13. The extent to which this will increase the comet’s brightness is subject to debate. Based on my own assessments, I estimate that the comet could brighten to a magnitude of -4, putting it in line with Venus. However, others are forecasting an even greater increase. The most optimistic prediction comes from Dutch amateur astronomer Gideon van Buitenen, who anticipates a peak magnitude of -6, nearly three times as bright as Venus!
Nevertheless, the chances of this extreme brightening occurring are minimal.
When to search for comet G3 ATLAS
Night sky live
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Currently, there seems to be a three-day window—January 12 through 14—for individuals in the Northern Hemisphere to glimpse G3 ATLAS.
Your initial chance will materialize early on January 12. From mid-northern latitudes, the comet will rise approximately 35 minutes prior to sunrise and will be situated 5 degrees directly above the sun at local sunrise. Therefore, beginning around 25 minutes before sunrise, methodically scan/sweep along the east-southeast horizon with binoculars to attempt to detect the comet.
On the evening of January 14, the comet will sink 35 minutes after the sun sets and at local sunset will be approximately 7 degrees nearly directly above the sun. Thus, starting about 10 minutes after sunset, leisurely proceed to scan/sweep along the west-southwest horizon with binoculars to attempt to catch sight of the comet.
How to observe comet G3 ATLAS
- Ensure that you possess a clear, unobstructed view towards the east-southeast and west-southwest horizons. The comet will be very close—just a few degrees—above the east-southeast horizon on Sunday morning and a similar distance above the west-southwest horizon on Tuesday evening. If possible, reaching a shoreline with a flat sea horizon or ascending a high hill above any surrounding obstructions (like tall trees or buildings) will provide you a distinct advantage. Moreover, you’ll want to hope for clear skies absent of low-lying clouds near the horizon.
- A quality pair of binoculars is crucial. Binoculars of 7×50 power are recommended, but if opting for a larger set, such as 11×80 binoculars, mounting them on a solid tripod will yield even better results.
- If visible, G3 ATLAS will present itself as a bright star, radiating a whitish or golden hue. If a tail is discernible, it will likely appear short or stubby and oriented almost directly upward, possibly slightly tilted to the right. After locating it with binoculars, try to see it with your unaided eye. The brighter the comet becomes, the more likely success will be yours.
To gauge angular degrees, keep in mind that your clenched fist at arm’s length measures approximately 10 degrees. Thus, 5 degrees would be about half a fist.
Is it possible to see G3 ATLAS during daylight?
Monday, January 13 is projected to be the day the comet achieves its peak brightness. As previously mentioned, predictions regarding its luminosity vary greatly, estimating between magnitude -3 to -6. Should G3 ATLAS reach magnitude -4 or stronger, then — theoretically — it may be bright enough to be observed during the daytime.
WARNING! Since the comet will be positioned merely 5 degrees above the sun, making an attempt to spot it during the day carries inherent risks. While direct observation of the comet is not harmful, looking at the sun — even for a moment — can inflict serious retinal damage without pain. Such damage can result in irreversible blindness.
Moreover, with the comet so closely approaching the sun, avoid trying to observe it during the day with binoculars!
The safest method to observe
The safest way to observe the comet’s close encounter with the sun is via your computer screen, courtesy of the Solar and Heliospheric Observatory (“SOHO”). Astronomers expect remarkable views of the comet utilizing SOHO’s LASCO (Large Angle and Spectrometric Coronagraph Experiment) C3 camera and accessing either near-instantaneous images or videos covering the previous 24 hours.
In October of last year, the public was intrigued when SOHO documented Comet Tsuchinshan-ATLAS gliding near the sun. Since its inception in 1995, SOHO has identified over 5,000 comets through LASCO C3 imagery.
Comet G3 ATLAS will be observable within the LASCO C3 imagery from January 11 at 20:00 UT (3:00 p.m. EST) until January 15 at 03:00 UT (10:00 p.m. EST on January 14). It is expected to come closest to the sun — a mere 4.9 degrees from its center — on January 13 at 13:00 UT (8:00 a.m. EST).
Should any significant updates arise, we will share them here at Space.com, so stay tuned!
Joe Rao functions as an instructor and visiting lecturer at New York’s Hayden Planetarium. He covers astronomy for Natural History magazine, the Farmers’ Almanac, and other publications. Follow us on Twitter @Spacedotcom and on Facebook.
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