C/2024 G3 ATLAS - THE SPLENDID COMET OF 2025

Closest to Sun on 2025 January 13 at 0.09AU.
Closest to Earth on 2025 January 14 at 0.93AU
Maximum magnitude -4 in mid-January 2025
Orbital period: 160,000yrs

C/2024 G3 ATLAS. 2025 January 22 at 11:00UT. Canon 6D + Sigma 200mm f/2.8. 3x30sec iso1600. FOV 10deg.
North below. imaged from Swan Hill, Victoria, Australia.
 

COMET C/2024 G3 ATLAS SURPRISE APPEARANCE

During October 2024, astronomers witnessed one of the brightest comets in recent years C/2023 A3 Tsuchinshan-ATLAS,
but following hot on its heels during January 2025 was a visitor that surprised and surpassed all expectations.

C/2024 G3 ATLAS was discovered on 2024 April 5 by the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS)
search program located in Rio Hurtado, Chile. ATLAS is a robotic astronomical survey and early warning system
optimized for detecting small near-Earth objects before they impact Earth. Since coming into operation in 2015,
it has discovered at least 87 comets to date.

C/2024 G3 ATLAS was calculated to be moving in a highly eccentric orbit that takes around 160,000 years to complete one orbit.
It had a very small perihelion (Solar) distance of 0.09AU, equivalent to 13 million kms, which was due to occur on 2025 January 13.
When first discovered, its intrinsic brightness was rather faint, which suggested that the comet was unlikely to survive
its solar approach and disintegrate prior to perihelion.

During December 2024, several observers kept a close eye on its development and sure enough,
it was running a couple of magnitudes brighter than expected.
At the turn of the year, on January 2, T. Lovejoy reported that an outburst of 2 orders of magnitude occurred.
The following morning, I estimated the comet at magnitude 2.0 with a strongly condensed 3' coma and short tail.
Using a pair of 15x70mm binoculars, a prominent dark lane or nuclear shadow was visible. Was this the death knell?

Fortunately, the comet continued to brighten and on 2025 January 11, it entered into the field of view of NASA’s SOHO LASCO C3 camera,
putting on a spectacular display with multiple dust tail striations spread out into an arc as it rounded the Sun.
I strongly recommend you watch the replay at NASA’s SOHO Movie Theatre located at: https://soho.nascom.nasa.gov/data/Theater/
Chose the C3 image at 1024 resolution and select dates 2025 January 12 to 15.

Several daylight reports occurred at perihelion passage and the comet reached the brightness of Venus, magnitude -4,
one of the rarest comets to be visible during daylight hours. One interesting observation was noted in the SOHO data in that the comet
appeared to peak a day later than expected, indicating that perhaps another outburst had occurred.
Some suggested that this comet was developing into the next “Great Comet”.
A great comet is one that becomes exceptionally bright that even a lay person can identify it.

The comet then gradually made its way into evening skies.
On the evening of 2025 January 16, I managed an observation only 30 minutes after sunset where I estimated it at magnitude -2 in bright twilight,
about the brightness of Jupiter. The comet’s Solar elongation was a mere 10 degrees.
This was the closest observation of a comet to the Sun that I had ever made, rivalling observations of the Great Comet McNaught in January of 2007.
The following night, it was easily visible to the naked eye with tail from 40 minutes after sunset,
estimating it at magnitude -1 with a bright dust tail at least 2 degrees long.

Then on 2025 January 18, I noted a considerable fading of the head from the previous night, about magnitude 0.5.
Soon after, reports on social media started to show that the nucleus had disrupted.
An excellent image sequence was captured by Hungarian astronomer Lionel Majzik which showed the nucleus diffusing out over a few days
into a narrow spine that gradually lengthened along the line of the dust tail.

Not surprising since we had predicted that it would not survive in the first instance!
At least the nucleus made it through to perihelion, which left us with a visible tail created before the disintegration event.

What followed over the next few nights was quite remarkable.

On the evening of 2025 January 22, it appeared as a headless comet with a tail visible to the unaided eye at least 15 degrees in length
arcing towards the east, its brightness comparable to that of a second magnitude star.
The tail displayed striations through binoculars and photos. These synchrones are created from timed releases of dust from the nucleus.

Conditions slowly improved during the following nights as the comet gained altitude and away from twilight,
but the length and surface brightness of the tail faded each night as it receded from the Sun and the Earth.

On 2025 January 28, the headless wonder was still visible to the unaided eye and of the third magnitude,
appearing more obvious than the SMC, with the tail arching 10 degrees long above the star Fomalhaut.
But by January 31, the tail appeared 9 degrees long and closer to fourth magnitude.

The beauty with following comets is that you never know what you are going to get.
C/2024 G3 ATLAS will no doubt be one of the finest comets that I have observed in my lifetime,
but I believe it missed out on obtaining Great status due to its nuclear disruption and fadeout.
A comet of this calibre usually appears on average once every 10 years.
We have been very fortunate lately with 2 fine comets appearing in the space of 3 months.

Finder Chart for C/2024 G3 ATLAS from January 17th



 for an observer located at 35 South latitude (taking in most Australian capital cities) 1-1.5 hours after sunset.

Observations

C/2024 G3 ATLAS on 2025 January 31 at 11:10UT. Location Swan Hill, Victoria, Australia. 35S 143E
The headless wonder is still visible to the unaided eye with the tail arching 9 degrees long in PA89, above Fomalhaut
The first few degrees of tail is very bright, and of approximately fourth magnitude, slightly fainter than the surface brightness of the SMC.
Comet altitude 7 degrees.
Sun altitude -18 degrees


C/2024 G3 ATLAS on 2025 January 29 at 11:10UT. Location Lake Boga, Victoria, Australia. 35S 143E
The headless wonder is still visible to the unaided eye with the tail arching 10 degrees long in PA85, to the left of Fomalhaut
The first 4 degrees of tail is estimated to shine at fourth magnitude, on a par with the surface brightness of the SMC.
Comet altitude 7 degrees.
Sun altitude -18 degrees
Image details: Canon 6D + Sigma lens at 100mm, f/2.8, iso 1600 15x30sec.


C/2024 G3 ATLAS on 2025 January 28 at 11:10UT. Location Swan Hill, Victoria, Australia. 35S 143E
The headless wonder is still visible to the unaided eye with the tail arching 10 degrees long in PA89, above Fomalhaut
The first 4 degrees of tail is very bright, and of approximately third magnitude, more obvious than the SMC.
Unfortunately, smoke from bushfires interfered with the view.
Get your views in before moonlight starts to interfere from Feb 2
Comet altitude 6 degrees.
Sun altitude -18 degrees
Image details: Canon 6D + Sigma lens at 75mm, f/2.8, iso 3200 13x30sec.

C/2024 G3 ATLAS on 2025 January 27 at 11:00UT. Location Swan Hill, Victoria, Australia. 35S 143E
The headless wonder is still visible to the unaided eye with the tail arching 10 degrees long in PA89, towards Fomalhaut
The first 4 degrees of tail is very bright, and of approximately third magnitude, more obvious than the SMC.
Comet altitude 6 degrees.
Sun altitude -18 degrees
Image details: Canon 6D + Sigma lens at 75mm, f/2.8, iso 3200 13x30sec.


C/2024 G3 ATLAS on 2025 January 24 at 11:30UT. Location Strathalbyn, South Australia. 35S 139E
It appears as a headless comet with a naked eye tail arching 15 degrees long in PA82.
brightness approximately of the third magnitude.
Comet altitude 5 degrees.
Sun altitude -17 degrees

C/2024 G3 ATLAS on 2025 January 23 at 11:30UT. Location Strathalbyn, South Australia. 35S 139E
It appears as a headless comet with a naked eye tail arching 15 degrees long in PA82.
brightness approximately of the third magnitude.
Comet altitude 4 degrees.
Sun altitude -17 degrees

C/2024 G3 ATLAS on 2025 January 22 at 11:00UT. Location Swan Hill, Victoria, Australia. 35S 143E
It appears as a headless comet with a naked eye tail arching 15 degrees long in PA82.
brightness approximately of the third magnitude.
Comet altitude 4 degrees.
Sun altitude -16 degrees


C/2024 G3 ATLAS on 2025 January 21 at 11:00UT. Location Swan Hill, Victoria, Australia. 35S 143E
It appears as a headless comet with a naked eye tail arching 15 degrees long in PA82.
brightness approximately of the second magnitude.
I noticed something odd with the naked eye. The sky background to the lower right of comet seemed really bright, tail?
Comet altitude 3 degrees.
Sun altitude 15 degrees


C/2024 G3 ATLAS on 2025 January 20 at 10:45UT. Location Swan Hill, Victoria, Australia. 35S 143E
The comets nucleus has disintegrated, as reported elsewhere.
It appears as a headless comet with a bright tail at least 2 degrees long to the unaided eye, 1 hour after sunset.
Difficult to estimate brightness but I would say comet is of the second magnitude.
Through 8x40 binoculars, the dust tail is faintly traceable to 10 degrees in PA85.
Comet altitude 4 degrees.
Sun altitude -12 degrees


C/2024 G3 ATLAS on 2025 January 18 at 10:30UT. Location Lake Boga, Victoria, Australia. 35S 143E
To the naked eye, the comet appeared 40 minutes after sunset.
Its brightness was similar to a star of 3rd magnitude, however applying extinction correction has the comet at approximate magnitude 0.5:
Considerable fading noted from the previous night.
Through 15x70m binoculars, a bright dust tail 2 degrees long in PA85 is visible.
Comet altitude 4 degrees.
Sun altitude -9 degrees


C/2024 G3 ATLAS on 2025 January 17 at 10:20UT. Location Swan Hill, Victoria, Australia. 35S 143E
Easily visible to the naked eye with tail from 40 minutes after sunset.
Its brightness was similar to Saturn, however applying extinction correction has the comet at magnitude -1.0:
Through 15x70m binoculars, a bright dust tail at least 2 degrees long in PA80 is visible.
Comet altitude 3 degrees. Sun altitude -8 degrees

C/2024 G3 ATLAS on 2025 January 16 at 10:10UT. Location Swan Hill
An estimate using 8x40mm binoculars was m1=-2.0 : with a strongly condensed 5' coma and 1 deg tail in PA80.
Magnitude corrected for atmospheric extinction using the average table.
Comet altitude 3 degrees. Sun altitude -6 degrees
Clear conditions.
No Comparisons - estimated of the 3rd magnitude with 4 mag extinction.
My first view of the comet post-perihelion


Comet C/2024 G3 ATLAS in outburst! 2025 January 3 at 18UT.
An estimate using 8x40mm binoculars = magnitude 2.0, coma 3' tail 15' in PA 250
In 15x70mm binoculars, a prominent dark lane or nuclear shadow is seen.
Comet altitude 6 degrees. Sun altitude -8 degrees.


2025 January 3 showing outburst development. Image credit: Terry Lovejoy