ALAN'S COMETS

TALLY ENTRIES 751-760

751. COMET PANSTARRS C/2021 S3          Perihelion: 2024 February 14.71, q = 1.320 AU

I commented in the previous entry that this new year of 2024 will quite likely be my final year of sustained visual comet observing. It is thus only fitting that it should be a busy year for comets, and indeed there are several bright and/or interesting ones that I have expectations of observing, some of which I have already picked up and others which are still on the way in. In keeping with that expectation, by the middle of January I had already added two new comets to my lifetime tally.

My second tally entry of 2024 -- the tenth comet of the "Dependable Dozen" -- is a long-period object discovered by the Pan-STARRS survey in Hawaii back on September 24, 2021, when it was located at a heliocentric distance of 8.92 AU and almost 2 1/2 years away from perihelion passage. Despite its distance it was nevertheless bright enough (around 19th magnitude) that I was able to obtain a couple of images of it a few days later (when it was still listed on the Minor Planet Center's Possible Comet Confirmation Page) via the Las Cumbres Observatory network, and the astrometric measurements from these are included on the comet's discovery announcement. This is, incidentally, the 30th Pan-STARRS-discovered comet that I have observed visually, of 303 Pan-STARRS-named comets at this writing, i.e., almost exactly 10%; since I have seen one of these on two different returns the name "PANSTARRS" now appears on my tally 31 times, in second place behind LINEAR (with 75 appearances).

Comet PANSTARRS is traveling in a somewhat steeply-inclined direct, or prograde, orbit (inclination 59 degrees). It has brightened steadily ever since its discovery, and was most recently at opposition in December 2022; various reports and images then and throughout the first few months of 2023 indicated a total brightness close to 15th magnitude and the presence of a distinct tail. After conjunction with the sun (45 degrees south of it) in July 2023 it began a slow emergence into the southern hemisphere's morning sky, although the elongation remained quite small for some time and the reports and images I have seen remained relatively scarce, with the images I did see showing the tail as becoming more and more prominent. The first visual observations from southern hemisphere observers, around early December, indicated a total brightness near 11th magnitude. I was finally able to obtain some LCO images of the comet in late December, which were consistent with this reported brightness and which showed the tail as being over 15 arcminutes long. I've had to wait a while longer to make my first visual attempt, but when I was able to do so on the morning of January 14, despite its being at an altitude of only 12 degrees (due to its declination of -34 degrees) I could easily detect it near magnitude 10 1/2, and even despite less-than-ideal sky conditions I could detect the initial few arcminutes of the tail.

         Images of Comet PANSTARRS C/2021 S3 I've obtained via the Las Cumbres Observatory network. LEFT: October 2, 2021 (eight days after the comet's discovery), from the LCO facility at Cerro Tololo Inter-American Observatory in Chile. The astrometric measurements from this image were included on the comet's discovery announcement. RIGHT: December 26, 2023, from the LCO facility at Siding Spring Observatory in New South Wales. This is the full 30x30 arcminute image; when examined under enhanced contrast the tail extends almost all the way to the edge.

Initial projections suggested that Comet PANSTARRS might become as bright as 7th magnitude and perhaps even flirt with naked-eye visibility, however it is presently running about two magnitudes fainter than those early projections; since it may be a first-time visitor from the Oort Cloud this is perhaps not especially surprising. It remains a morning-sky object for the next few months, being currently located in northeastern Lupus about one degree northwest of the star Chi Lupi and traveling towards the northeast at slightly under one degree per day; over the next few weeks it crosses through Scorpius (passing 1 1/2 degrees southeast of the bright star Antares on January 30), Ophiuchus (passing 20 arcminutes southeast of the globular star cluster M9 on February 13 and 10 arcminutes southeast of the globular star cluster NGC 6356 a day later), Serpens Cauda, Aquila, Sagitta, and Vulpecula (crossing the western regions of the "Coathanger Cluster" Collinder 399 on March 30), before entering Cygnus during the second week of April. The comet is closest to Earth (1.29 AU) on March 15 and may be near its brightest -- perhaps a magnitude or so brighter than it is now -- around that time.

Comet PANSTARRS curves gradually more and more directly northward as it crosses the dense star fields of the Cygnus Milky Way during late April, and passes through its stationary point at the end of May. Shortly thereafter it enters northern circumpolar skies, passing just over half a degree west of the nearby spiral galaxy NGC 6946 on June 14 and subsequently traveling essentially westward through southwestern Cepheus and then Draco as it reaches its peak northerly declination (+62.8 degrees) on July 10 and goes through opposition a week later. The comet goes through its other stationary point just before the end of August and after that travels towards the southeast (gradually curving more directly eastward) as it starts to disappear into evening twilight around February 2025. It will almost certainly have faded below the limit of visual detectability well before then, probably around the July/August timeframe.

INITIAL OBSERVATION: 2024 January 14.51 UT, m1 = 10.4, 1.5' coma, DC = 3-4, 3.5' tail in p.a. 255 (41 cm reflector, 70x)

 

752. COMET 13P/OLBERS          Perihelion: 2024 June 30.02, q = 1.175 AU

This is a comet that I have been diligently awaiting for quite some time. Among other things, it is the 11th comet of the "Dependable Dozen" to show up on my tally; only one more of that particular group remains to be added, and that is still several months away. This is one of the "classical" Halley-type comets, and about a quarter-century ago I learned that it, along with another such comet, 12P/Pons-Brooks, would be returning in 2024 -- which was quite a ways in the future at that time but which the wheel of time has now brought to the present. I picked up Comet Pons-Brooks a little over six months ago (no. 740), and it has undergone several outbursts since then and is presently visible in binoculars near 8th magnitude, low in the northwestern sky after dusk. And now, I have picked up this one as well . . .

The comet was originally discovered on March 6, 1815 by the German astronomer Heinrich Olbers, who is perhaps best known as being a member of the "Celestial Police" that formed in 1800 to search for a presumed planet between Mars and Jupiter. Although the "Police" were beaten at this task by the Sicilian astronomer Giuseppe Piazzi, who discovered what is now known as the asteroid (1) Ceres at the beginning of 1801, Olbers nevertheless went on to discover two of the next three known asteroids, (2) Pallas in March 1802 and (4) Vesta in March 1807. (Vesta was the first destination for NASA's Dawn spacecraft, which orbited it from mid-2011 to mid-2012.) Olbers also discovered two long-period comets, in 1780 and 1796, and is also known for articulating what is now known as "Olbers' Paradox" (concerning the darkness of the nighttime sky) in 1823.

Olbers' comet reached a peak brightness between 5th and 6th magnitude around the time of its perihelion passage in late April 1815. The observations during that return were sufficient to show that the comet had an orbital period of slightly over 70 years, with a perihelion passage expected in the mid- to late 1880s. It was "discovered" (as an apparently unknown comet) by the champion American comet discoverer William R. Brooks on August 25, 1887, with subsequent calculations soon showing its identity with Olbers' comet and a perihelion passage in early October. A somewhat distant approach to Jupiter (1.52 AU) in early 1889 shortened the orbital period slightly, to just under 70 years, and the comet was next recovered by then-Czechoslovakian astronomer Antonin Mrkos -- discoverer of several comets in the mid-20th Century, including the bright naked-eye Comet Mrkos 1957d -- in January 1956. Comet Olbers passed through perihelion in mid-June and reached a peak brightness near 7th magnitude, and was followed until late September.

     LEFT: Comet P/Olbers as sketched by William R. Brooks on October 14, 1887. RIGHT: Photograph of Comet P/Olbers taken by George Van Biesbroeck from Yerkes Observatory in Wisconsin on June 30, 1956.

As Comet Olbers was approaching its 2024 perihelion it occurred to me that I might be able to make the recovery. I began making attempts with the telescopes of the Las Cumbres Observatory network in early October 2022, and after an initial false alarm I continued to make unsuccessful semi-regular attempts up through mid-January 2023, after which the comet began disappearing into twilight. It was in conjunction with the sun in early May, and after it began emerging into the morning sky I made my next attempt in mid-June, and thereafter continued making attempts on a roughly semi-monthly basis. As before, these various attempts were all unsuccessful.

On August 24, 2023 I took two 10-minute exposures with one of the 1.0-meter LCO telescopes based at Siding Spring Observatory in New South Wales. When I examined these images I spotted a very faint (22nd magnitude) moving starlike object near the expected line of variation at a perihelion difference of -0.73 days (approximately 17.5 hours) compared to the Minor Planet Center's prediction. I immediately ordered up a new set of images to try to confirm this, but in the meantime, armed with the knowledge of exactly where to look, I was able to spot extremely faint images on a pair of exposures I took with one of the 1.0-meter LCO telescopes at the South African Astronomical Observatory on August 13, that were consistent with my August 24 suspect. (These images were very weak, and I am not surprised that I failed to notice them at the time.) Meanwhile, two different pairs of images I obtained via the LCO telescopes at SAAO on the 25th showed the same moving object in a location that was consistent with my suspect, as did images I obtained over the next couple of nights with LCO telescopes at both locations based upon a preliminary orbital calculation by Syuichi Nakano that utilized my astrometric measurements as well as a linkage with measurements made in 1887 and 1956. I received notification from the Minor Planet Center that my recovery looked good, and in addition to acknowledgement on the next Minor Planet Electronic Circular of comet positions and orbits, I was officially credited with the recovery by the Central Bureau for Astronomical Telegrams and by a press release issued by LCO. Needless to say, I have found this all quite gratifying, and I glad that all the effort I put into these recovery attempts paid off.

     The recovery images of Comet 13P/Olbers, taken on August 24, 2023 with a 1.0-meter LCO telescope based at Siding Spring Observatory in New South Wales. These are consecutive 10-minute exposures.

Ever since my recovery I have continued to image Comet Olbers on a roughly bi-weekly basis, and of course other observers have imaged it as well. It brightened steadily during the intervening weeks, as well as developing a distinct coma and the apparent beginnings of a short tail in the process. LCO images I took during January 2024, including a set I obtained on January 29, revealed its continued brightening, and suggested that the comet might now be bright enough to be worth attempting visually. On my first attempt, on the evening of February 1, I successfully detected it as a faint, somewhat condensed object of magnitude 13 1/2. (I had hoped to be the first observer to pick it up visually, but it appears I was beaten to the punch by my colleague Chris Wyatt in New South Wales, who picked it up a little over 15 hours before I did.) The overall brightness and appearance were similar when I observed the comet again three nights later.

      Images of Comet 13P/Olbers I obtained via the 0.35-m LCO telescope at the South African Astronomical Observatory. Both images are 3-minute exposures. LEFT: January 3, 2024. RIGHT: January 29, 2024.

Comet Olbers is traveling in a moderately-inclined direct (or prograde) orbit (inclination 44.5 degrees). As is also the case with Comet Pons-Brooks, the viewing geometry during this return is rather mediocre, with the comet's being on the far side of the sun from Earth when at perihelion; for what it's worth, those of us in the northern hemisphere will certainly have the better view. The return is fairly similar to that of 1956, with the date of this year's perihelion being just two weeks later than the corresponding date from that year.

The comet was at opposition just after mid-November 2023 and is presently in the evening sky, being currently located in far northwestern Eridanus 2 1/2 degrees southwest of the star 5 Eridani and traveling almost due northward at 20 arcminutes per day. Over the coming weeks it curves toward the northeast and accelerates, crossing into Cetus in mid-February (and passing half a degree east of the star Alpha Ceti on February 29), into Taurus during the latter part of March (and passing between the Pleiades and Hyades star clusters during mid-April), and then into Auriga during the second week of May, where it passes 10 arcminutes southeast of the open star cluster M36 on May 21. In early May the elongation drops below 30 degrees, by which time the comet is traveling towards the east-northeast at 40 arcminutes per day, and the elongation reaches a minimum of 26 degrees at the end of the month. Shortly after mid-June the comet crosses into Lynx, and it reaches a maximum northerly declination (+42.4 degrees) on June 30 (the date of perihelion passage), at which time the elongation goes back over 30 degrees.

Now traveling towards the east-southeast, Comet Olbers crosses northeastern Leo Minor during the second half of July, being nearest to Earth (1.89 AU) on July 20, when its elongation is 35 degrees and it will be traveling at its maximum rate of slightly over 1 degree per day. Shortly before the end of July the comet crosses into southwestern Ursa Major and then into Coma Berenices two weeks later; during the middle days of August it passes directly across the Coma Berenices Star Cluster (Melotte 111). The elongation reaches a maximum of 40 degrees around August 23, and the comet crosses into Bootes in early September and then into Virgo during the last week of that month.The elongation again drops below 30 degrees during the second week of October, and within another couple of weeks the comet disappears into evening twilight.

The historical data seems to suggest that Comet Olbers brightens fairly rapidly as it approaches perihelion, and indeed its recent behavior supports this. It may be between 10th and 11th magnitude during March, between 9th and 10th magnitude during April, and perhaps 8th magnitude during May. (Curiously, during mid-April Comets Pons-Brooks and Olbers -- traveling in opposite directions -- will pass some 17 degrees from each other, with Pons-Brooks being a few magnitudes brighter but quite a bit lower in the sky.) Comet Olbers should reach a peak brightness between 6th and 7th magnitude during June and July and should then fade afterwards, but may still be around 10th of 11th magnitude when it disappears into the dusk during October. For what it's worth, I have read one report from 1956 that suggests that, about six weeks after perihelion passage, the comet might have undergone an outburst to about 6th magnitude; perhaps we might see something like that this time around.

Comet Olbers has a rather deep personal significance to me, which is perhaps a good part of the reason why I invested so much effort into my attempts to recover it. Its previous return in 1956 came less than two years before I was born, and, indeed, my parter Vickie's parents were married in September 1956, just before the final observations of that return were made. And, it is bringing more significant events to my personal life: on the day before I picked it up Vickie and I, who began dating seven years ago and after five years of living together as a "domestic partnership," agreed to get married later this year (date undetermined at this writing, but probably sometime during the summer). And then, on February 4, my older son Zachary and his partner Karina welcomed into the world their first (and what may very well be their only) child, my newest grandson Santiago Ezekiel. This is my second biological grandchild, and my third grandchild overall.

With regard to the "retirement" from visual observational activities that I have often discussed in these pages, my original thought had been to do so once I was finished with Comet Olbers, however the discovery last year of Comet Tsuchinshan-ATLAS C/2023 A3 (no. 749) and its potential bright display later this year has caused me to delay that event until around the year of this year. As for Comet Olbers, it should still be followed with larger telescopes for some time, and I may even try to image it myself from time to time with the LCO telescopes; around the time of its opposition in June 2025 it will be traversing the very rich star fields of the Sagittarius Milky Way. It so happens that the next return, in 2094 (perihelion late March) will be the most favorable one since its original discovery, with its passing 0.76 AU from Earth and probably reaching a peak brightness of at least 5th magnitude. I will be long gone well before then, of course, but perhaps one or more of my grandchildren -- all three of whom will be a bit older then than I am now -- will be able to see it, or -- perhaps even more likely -- one or more of their children may see it and, in a sense, carry on my personal story with this most memorable comet.

INITIAL OBSERVATION: 2024 February 2.09 UT, m1 = 13.6, 0.7' coma, DC = 3-4 (41 cm reflector, 229x)

 

753. COMET 207P/NEAT          Perihelion: 2024 January 31.82, q = 0.938 AU

In a tally entry that I wrote a little over seven months ago, at which time I was about ready to enter the "home stretch" towards comet no. 750, I introduced the "Dependable Dozen," i.e., twelve comets that I expected to observe, and add to my tally, before the end of 2024. Since I added my 750th comet earlier this year the entire rationale for the "Dependable Dozen" may perhaps be a bit moot now, although as I've continued to add those particular comets I have nevertheless made mention of it. As I mentioned in its entry, the preceding comet was the 11th comet of that group, but the final member is still a few months away. Meanwhile, in the original discussion I made mention of several "maybes," and some of the comets that I have added during the intervening months have been among this group. This particular comet is another one of those "maybes."

The comet was originally discovered in May 2001 during the course of the Near-Earth Asteroid Tracking (NEAT) program that was developed and supervised by planetary scientist Eleanor "Glo" Helin; the discovery telescope was based at Haleakala Observatory in Hawaii. Calculations soon showed that it was rather faint intrinsically, and was a short-period object with an approximate orbital period of 7.7 years that was already two months past perihelion when discovered. Japanese astronomer Syuichi Nakano pointed out that the comet's orbit bears a rough similarity to that of the famous disintegrated Comet 3D/Biela, although the resemblance is rather superficial and is almost certainly nothing more than coincidence.

Comet NEAT next returned in 2008 and was duly recovered and numbered. The viewing geometry was somewhat favorable, and the reported brightnesses were enough to convince me that visual attempts might be worthwhile, however I was unsuccessful in detecting it. At the next return, in 2016, the viewing geometry was very unfavorable and the comet was not recovered.

On its present return Comet NEAT was recovered by French astronomer Francois Kugel on August 14, 2023, at which time it was a very faint and starlike object of 21st or 22nd magnitude. For the next few months it remained faint and essentially starlike, and only within the fairly recent past has it begun to brighten and display typical cometary activity like a coma and a tail. I first began imaging it with the Las Cumbres Observatory network in early January 2024, and the most recent set of images I took, on February 3, together with a recent report of a successful visual observation, suggested that it was now worthwhile for me to attempt visually. On the evening of February 4 -- the same day that my newest grandson Santiago Ezekiel was born -- I was able to detect it as a very faint and small object of 14th magnitude, that exhibited distinct motion over an interval of 20 minutes.

     LEFT: Comet 207P/NEAT on February 3, 2024, as imaged by the Las Cumbres Observatory facility at McDonald Observatory in Texas. RIGHT: My older son Zachary, his partner Karina, and my new grandson Santiago Ezekiel, born on February 4, 2024, the same day that I added Comet NEAT to my tally.

Comet NEAT's current return is, by far, the most favorable one that it has had since its discovery. Although perihelion passage was a week ago it is still approaching Earth, and will pass a relatively close 0.220 AU from our planet on March 5. Presently it is located in southeastern Cetus a couple of degrees southwest of the star Sigma Ceti and is traveling almost due eastward at roughly 1 1/4 degrees per day; over the next few weeks it accelerates and gradually curves northward, crossing through Eridanus, Lepus, and then Monoceros. At the time of its closest approach to Earth it will be located about 2 1/2 degrees north of the star Theta Leporis and traveling at its maximum rate of slightly under three degrees per day. The comet may brighten to perhaps 13th magnitude by the time of its approach, but once it begins receding from Earth it will likely commence fading quite rapidly, and will probably drop below the limit of visual detectability by the latter part of March. At most, I will probably only be getting a handful of visual observations of it.

For what it's worth, three returns from now, in 2047, Comet NEAT will pass 0.16 AU from Earth -- about the closest possible approach in its current orbit -- in early February, and should reach a peak brightness near 12th magnitude. Even if I am still alive at the age of 88 I have no expectations of observing it then -- especially since it will be traveling through southern circumpolar skies throughout most of that time -- but hopefully the comet observers of that era will be able to follow it well.

With the addition of Comet 207P/NEAT to my tally I have now observed 152 numbered periodic comets (of 472 periodic comets that have been numbered as of this writing). One periodic comet that I observed on its discovery return -- Comet NEAT P/2001 Q6 (no. 296) -- has recently been recovered, and will automatically give me my 153rd numbered periodic comet when it receives a permanent number, which should be taking place within the relatively near future. (I have already imaged this comet via LCO, and it is conceivable that I might observe it visually around the time of its perihelion passage in late February, although the viewing geometry is only mediocre at best and the comet will likely remain too faint for visual detectability.) One other periodic comet that has recently been recovered (and that I have also imaged via LCO) and which should be numbered shortly may conceivably become bright enough for visual observations when it passes through perihelion a few months from now. There are a handful of other periodic comets that I observed on their respective discovery returns that may eventually be recovered and numbered at some point in the future, which accordingly would continue to give me additional numbered comets on my "observed" list from time to time. However, unless I continue observing at something other than a minimal level beyond my planned "retirement" at the end of this year, there are no additional already-numbered periodic comets that I have any reasonable expectations of adding to that list; 207P/NEAT was the last remaining member of that particular group of comets.

INITIAL OBSERVATION: 2024 February 5.10 UT, m1 = 13.9, 0.4' coma, DC = 2-3 (41 cm reflector, 229x)

UPDATE (February 17, 2024): The newest batch of Minor Planet Circulars has assigned the designation 473P to Comet NEAT P/2001 Q6 which, as I noted above, gives me my 153rd numbered periodic comet as well as the highest-numbered periodic comet that I have observed (the overall highest-numbered comet now being 480P). The most recent images I have taken of Comet 473P/NEAT via the Las Cumbres Observatory network indicate that is continuing to brighten as it approaches perihelion, although whether or not it becomes bright enough to be detectable visually remains to be seen.

Meanwhile, Comet 207P/NEAT has, as expected, brightened somewhat, being near magnitude 13 1/2 when I last saw it a few nights ago. Moonlight is now precluding further observations for the time being, but hopefully once we are past full moon the comet will have brightened further as it nears its closest approach to Earth.

MOST RECENT OBSERVATION: 2024 February 14.09 UT, m1 = 13.6, 0.8' coma, DC = 2-3 (41 cm reflector, 229x)

 

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