As I have been discussing in numerous previous entries, and as I wrote in the text of my new "Comet Page," at the end of 2024 I "retired" from systematic visual comet observing, after 55 years at this endeavor and with my lifetime comet tally standing at 760. But as I also wrote in the new page, for at least the near-term future I am not walking away from visual comet observing altogether, but will continue to make efforts to observe bright and/or interesting comets that might comet along, although this will be on an occasional rather than a systematic basis. (I also expect to continue my imaging activities via the Las Cumbres Observatory network and my collaboration with its Global Sky Partners educators' forum.) As I have done for the past several years, I will continue to write up descriptions of any additional comets I add to my tally, and post them to these pages.

My first "post-retirement" tally addition certainly qualifies as a "bright and/or interesting" comet. It was discovered on April 5, 2024 by the ATLAS program's Chile telescope, a 19th magnitude object in southern circumpolar skies near a declination of -74.5 degrees. I obtained my first set of images of it via the LCO network five days later, and the astrometrical measurements from this set and another set of images I obtained on the 16th were included in the comet's discovery announcement. Even as early as that second set of images I could detect a short tail extending towards the north-northwest.

As soon as the first orbital calculations were published, Comet ATLAS' extremely small perihelion distance called almost immediate attention to it. A comet approaching that close to the sun might very well not survive perihelion passage, however as additional observations and calculations began to show that Comet ATLAS is apparently not a first-time visitor from the Oort Cloud -- the previous return having taken place approximately 190,000 years ago -- these seemed to suggest that there was at least some chance it might survive perihelion and, conceivably, put on a respectable show. The comet is traveling in a steeply-inclined retrograde orbit (inclination 117 degrees) and, unfortunately for those of us in the northern hemisphere, the orbit is oriented such that the comet both approaches and recedes from the sun from almost directly south of it, and would only be north of the sun, and accordingly accessible from the northern hemisphere, for a very brief interval around perihelion, when, of course, it would be located very close to the sun.

I continued to image Comet ATLAS via LCO on a semi-regular basis up through the end of August (after which its elongation became too small for the LCO telescopes to access); by my last set of images it had brightened to about 17th magnitude and was displaying a distinct tail several arcminutes long. The earliest visual observations of which I'm aware were made by observers in the southern hemisphere in late October, which indicated a brightness near 12th magnitude -- as much as two magnitudes brighter than expected, which in turn suggested a higher probability of surviving perihelion passage. The southern hemisphere observers continued to make additional observations into early November, which indicated a slight brightening, but shortly thereafter the comet went into conjunction with the sun (roughly 28 degrees south of it) and, for a time at least, observations were no longer possible.

Comet ATLAS began emerging into the southern hemisphere's morning sky around the beginning of December, although it remained at a small elongation -- initially around 20 degrees, decreasing to 18 degrees by month's end. Observations continued to show it running about two magnitudes brighter than originally expected, and by the end of 2024 observers in the southern hemisphere were reporting brightnesses around 6th magnitude. A few days later, however, the comet underwent a distinct outburst, to about 2nd magnitude, and despite an elongation of only 16 degrees several observers reported naked-eye sightings. Comet ATLAS continued to brighten from that point as it approached the sun, being about 1st magnitude when it began disappearing into morning twilight around January 11. By this time the comet had traveled far enough north such that observers in the northern hemisphere also began reporting observations and images.

      LEFT: The final image I took of Comet ATLAS via the Las Cumbres Observatory network, obtained August 29, 2024 from the LCO facility at Cerro Tololo Inter-American Observatory in Chile. RIGHT: Comet ATLAS as photographed by astronaut Donald Pettit aboard the International Space Station on January 11, 2025. Courtesy NASA.

Beginning on January 11, Comet ATLAS entered the field-of-view of the LASCO C3 coronagraph aboard SOHO, where it would remain for the next four days. Its high brightness in the LASCO images rather strongly suggested that it might be visible during daytime, and, indeed, several observers soon successfully took daytime images and/or reported successful daytime observations. Eighteen years ago I had used a 20-cm SCT and altitude/azimuth offsets from the sun to make successful daytime observations of Comet McNaught C/2006 P1 (no. 395), and I decided I would use the same instrument and procedure to attempt daytime observations of Comet ATLAS. Bad weather and clouds precluded any realistic attempts for a couple of days, but, finally, on January 14 I had clear skies, and shortly after 11:20 A.M. I managed to spot the comet -- then at an elongation of just under 7 degrees -- although I lost it in the bright sky after about a minute. A little less than an hour and a half later I spotted it again, and successfully followed it for the next half-hour. It appeared as a bright central condensation with a faint trace of coma and the beginnings of a slightly curved tail. Under the circumstances the making of a formal brightness measurement would be somewhat problematical, but the comet definitely appeared fainter than I remember for Comet McNaught, and I accordingly "guesstimated" the brightness as being near magnitude -2.

    LEFT: Comet ATLAS in the LASCO C3 coronagraph aboard SOHO on January 14, 2025, at roughly the same time as my initial sighting. Courtesy NASA/ESA. RIGHT: Daytime image of Comet ATLAS taken by Monika Landy-Gyebnar in Hungary on January 14, 2025, roughly 10 hours before my initial sighting. The comet's appearance in this image approximates what I saw through the 20-cm SCT. Image used with permission.

Shortly thereafter Comet ATLAS began emerging into bright twilight in the evening sky, and several observers took images and reported successful observations. I do not have a good horizon in that direction from my home location, so I made arrangements to view the comet on the evening of the 15th from the parking lot of the New Mexico Museum of Space History in Alamogordo (which is located on a mountainside above the city and which has a good view of the far western horizon). Unfortunately, some thick cirrus clouds began moving into the southwestern sky during the hours immediately preceding my observing session, although I nevertheless did set up my 10-cm SCT in case there was some clearing. As things turned out, I did successfully see the comet for about 30 seconds when it passed through a brief gap in the clouds just over 20 minutes after sunset when, at an elongation of just under 10 degrees, it was located some 4 degrees above the horizon. Once it disappeared behind a thick cloud at the bottom of that gap, that was the end of its visibility. The comet exhibited a bright central condensation and the beginnings of a curved tail a few arcminutes long; I would "guesstimate" its brightness as being somewhere near magnitude -1.

For me, Comet ATLAS is already gone. Theoretically it has remained accessible in the evening sky and may continue to be so for a couple of more nights, although it is only marginally higher above the horizon than it was on the 15th, and with less-than-ideal weather prospects (and my reluctance to embark on another two-hour roundtrip drive to Alamogordo for what might very well end up being the proverbial "wild goose chase") I have made no plans for further observation attempts. Furthermore, the comet is plunging southward fairly rapidly -- thus quickly becoming inaccessible again from the northern hemisphere -- and since it is now receding from the sun and Earth it is also fading.

For observers in the southern hemisphere, meanwhile, the conditions for visibility are rapidly improving, and it is entirely possible that they may witness a pretty good show over the next two to three weeks -- indeed, initial reports at this writing do suggest a relatively decent display could be in the works. The comet remains somewhat low in the evening sky, however, with the elongation not going above 30 degrees until almost mid-February and not above 40 degrees until mid-March. It is in conjunction with the sun (48 degrees south of it) at the beginning of April, at which time it will probably be close to fading beyond visual detectability.

The current view of Comet ATLAS from the southern hemisphere. This image was taken by Rob Kaufman from near Bright, Victoria, Australia on the evening of January 17, 2025. Used with permission.

This sort-of "extra" comet to my tally is unique and at or near record-breaking in several respects. It has the 4th-smallest perihelion distance of any comet on my tally, and at the time of my first sighting on January 14 its heliocentric distance was 0.119 AU, the smallest heliocentric distance at which I've ever observed a comet. Comet ATLAS becomes only the third comet that I have observed during daytime, a total that includes Comet Hale-Bopp C/1995 O1 (no. 199) which I sucessfully followed for one minute after sunrise one morning before losing it in the bright sky; it is the only comet I have ever added to my tally during daytime. At magnitude -2 it is the 3rd-brightest comet I have ever seen, and it is the brightest comet I have ever observed on my initial observation. Since I never observed Comet ATLAS with my naked eye (or even with binoculars) I don't consider it a "Great Comet" (at least, from my perspective), but the fact I could observe it during daytime does warrant consideration as being among my "best" comets; I accordingly rank it as the 8th-best comet I have ever observed.

INITIAL OBSERVATION: 2025 January 14.84 UT, m1 = -2:, 0.5' coma, DC = 8, 2' tail in p.a. 050 (20 cm SCT, 80x; daytime)

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