TALLY ENTRIES 701-710
|701. COMET 7P/PONS-WINNECKE Perihelion: 2021 May 27.11, q = 1.234 AU
I have now begun my eighth "century" of comets -- something which, in all honesty, I do not expect to complete. I do so with a pair of short-period comets that I have seen on previous returns, and thus for the time being my total of separate comets remains at 499; since the only comets that I have a realistic chance of adding to my tally within the short-term future are other short-period objects that I have seen before, barring a bright new discovery sometime soon it may be a few months before I am able to pick up my 500th separate comet.
This particular comet has a rather long and interesting history. It was initially discovered by the champion French comet hunter Jean Louis Pons in June 1819, and then followed for the next six weeks before disappearing into sunlight en route to a rather close approach to Earth (0.13 AU) shortly after mid-August. The German mathematician Johann Encke -- at that time engaged in orbital calculations of the comet that now bears his name -- calculated an orbital period of about 5.6 years for Pons' comet, but this orbit apparently was not sufficiently accurate to predict a future return, and it became lost. It was finally re-discovered as a new comet in March 1858 by the German astronomer Friedrich Winnecke, and very quickly thereafter the astronomers of that era recognized it as being identical to Pons' 1819 object.
Comet Pons-Winnecke has been recovered at most of its returns since then. With an orbital period that has remained within the general vicinity of 6 years (presently 6.3 years), it has undergone repeated close approaches to Jupiter which, over time, have acted to increase its perihelion distance, from around 0.78 AU at the time of Pons' and Winnecke's discoveries, to around 1.0 AU around the beginning of the 20th Century, to roughly 1.25 AU ever since the middle of the 20th Century. A rather remarkable series of returns took place during the 1920s and 1930s when it made several close approaches to Earth, including to 0.14 AU in June 1921 and to 0.11 AU in July 1939. The most dramatic approach took place on June 26, 1927, when the comet passed just 0.039 AU from Earth -- the second-closest confirmed cometary approach to Earth during the entire 20th Century -- and briefly became as bright as 4th magnitude with a 1-degree-wide coma that traveled southward at up to 11 degrees per day. This approach enabled the first serious attempts to determine the size of a cometary nucleus, with most investigations suggesting a diameter on the order of a few km -- close to the presently accepted value of 5.2 km.
These approaches also brought with them a meteor shower, the June Bootids, that produced strong displays -- up to several hundred meteors per hour -- in 1916, 1921, and 1927. Perturbations by Jupiter have now moved the June Bootid meteor stream away from Earth's orbit and there haven't been any strong displays since then -- with the exception of a brief outburst of over 100 meteors per hour that was witnessed from Japan, Europe, and Canada in 1998. Since the comet was 2 1/2 years past perihelion at the time and was no longer making close approaches to Earth, the cause of this particular shower remains somewhat of a mystery.
Following the comet's placement into something close to its present orbit following a somewhat distant approach to Jupiter (0.94 AU) in 1953, visual observations all but ceased for several returns, and essentially all the observations obtained of it were via short-exposure photographs taken for astrometric purposes. Since these tend to produce very faint brightness measurements, this led to a general speculation that Comet Pons-Winnecke had undergone a significant diminishing of its intrinsic brightness. In the early 1980s this conclusion was challenged by a Dutch amateur astronomer, Reinder Bouma, who pointed out that the viewing circumstances at the coming return in 1983 were favorable and that it might still be detectable visually.
Bouma's prediction, which was published in an Australian journal, was not widely circulated, but a few observers in Austalia succeeded in observing it at around 12th magnitude. I learned of this -- and was quite surprised -- when I arrived in Australia in mid-June for a visit to that country following the total solar eclipse that I had viewed from the Indonesian island of Java earlier that month, and by using a telescope owned by observing assistant Tom Cragg at Siding Spring Observatory in New South Wales successfully detected it near magnitude 12 1/2 (no. 59). I managed to obtain one additional observation, very low in the southeastern sky, after my return to the U.S. a week later.
I searched for Comet Pons-Winnecke a handful of times during the mediocre-geometry return in 1989 but failed to detect it, and did not attempt it during its unfavorble return in 1996. The next return, in 2002, was a relatively good one, with a minimun distance from Earth of 0.63 AU taking place in early June, and I successfully followed it for two months (no. 309) as it reached a peak brightness of 12th magnitude. The return in 2008 was another mediocre one although I did search for it a couple of times, unsuccessfully, and again I did not attempt it during the unfavorable return in 2015. On its present return the comet was recovered as long ago as January 7, 2020 by the Mount Lemmon Survey in Arizona, as a very faint object close to 22nd magnitude. It was followed for a few weeks after that, and after conjunction with the sun last August has been under more-or-less continuous observation since late last year, although until recently it has remained an essentially inactive object. Only within the past few weeks has it started to show some activity, and I made one unsuccessful visual attempt for it in late April; during my first attempt of the current dark run, on the morning of May 9, I successfully detected it as a small and moderately condensed object slightly brighter than 14th magnitude.
. LEFT: A set of five "stacked" CCD images (total exposure time 9 minutes) I took of Comet 7P/Pons-Winnecke on June 13, 2002, during its return that year (no. 309). RIGHT: A 5-minute exposure of Comet 7P/Pons-Winnecke I took via the Las Cumbres Observatory facility at Teide Observatory in the Canary Islands on May 8, 2021, slightly over 24 hours before my first visual observation on the current return.
It so happens that this year's return of Comet Pons-Winnecke is the best one it has made during my lifetime thus far, with a minimun distance from Earth of 0.44 AU taking place on June 12. It remains in the morning sky throughout most of its period of visual detectability, at present being located in eastern Aquila about one degree east of the star Theta Aquilae and traveling towards the east-southeast at slightly over one degree per day. It crosses into Aquarius shortly after the middle of May and remains within that constellation for the next few weeks (with the exception of the first week of June, when it crosses far northeastern Capricornus), and when closest to Earth it will be located some two degrees north of the star 41 Aquarii. Over time the comet turns more and more directly southward, crossing into northeastern Piscis Austrinus during the fourth week of June and passing 1 1/2 degrees northeast of the bright star Fomalhaut on June 25 before crossing into Sculptor a couple of days later (and passing 15 arcminutes northeast of the bright spiral galaxy IC 5332 on July 7) then into Phoenix (and dropping south of declination -40 degrees) in mid-July. It goes through its stationary point in early August and drops south of declination -50 degrees a week later, before reaching a peak southerly declination of -52 degrees at the end of that month and being at opposition shortly before mid-September. While the comet is heading in a generally northward direction at that time, it remains moderately deep in southern skies for quite some time thereafter, finally going back north of declination -40 degrees shortly before the end of October.
Although my evidence for this is somewhat spotty, my observations -- both successful and unsuccessful -- of Comet Pons-Winnecke during previous returns suggests it may exhibit an asymmetric brightness behavior similar to that of Comet 6P/d'Arrest (which returns later this year, incidentally), i.e., remaining faint and relatively inactive until shortly before perihelion, and then brightening almost explosively before diffusing out and fading away gradually; its brightness thus far during the present return seems to be consistent with this. If it indeed exhibits such a behavior, the comet should brighten rapidly over the next few weeks, reaching a peak brightness of 11th magnitude, perhaps even 10th, around the time it is nearest Earth in mid-June. As it fades I should be able to follow it until probably sometime in July, although its increasing southern declination will start to make observations a bit difficult before long; observers in the southern hemisphere should be able to follow it visually until at least August and possibly September.
After staying relatively far away from Jupiter for over half a century, Comet Pons-Winnecke finally encounters that planet again (at a distance of 0.65 AU) in September 2025, which will drop its perihelion distance down to 1.13 AU. Additional approaches to Jupiter in 2037 and 2049 will decrease its perihelion distance further to about 0.85 AU -- not much greater than that during its original discovery returns -- by the middle of the 21st Century. Despite this, even without considering the "retirement" from visual comet observing that I have been discussing off and on during previous tally entries, I will almost certainly not see this comet after this year's return, since the next three returns (in 2027, 2033, and 2039) all take place under geometry similar to that of the returns in 1989 and 2008. It makes approaches to Earth of 0.21 AU in July 2045 and 0.17 AU -- which takes place almost directly sunward of Earth -- in June 2062, but I will leave observations of those encounters to the comet observers of those eras.
Although the primary focus of my lifetime observational activities has been on comets, I have often observed other transient phenomena as well, including novae and supernovae, at least those that have been relatively bright. In the general slowdown in observational activity that I have been undergoing during the recent past I have not been expending much effort on such events, and, indeed, despite the fact that at least three relatively bright novae have appeared earlier this year I didn't observe any of them or had any plans to do so. However, a recent report announced that one of these novae, Nova Cassiopeiae 2021 (aka V1405 Cassiopeiae), which had been discovered on March 18 by Japanese amateur astronomer Yuji Nakamura -- one of the discoverers of Comet Cernis-Kiuchi-Nakamura 1990b (no. 139) and among those who independently re-discovered Comet 122P/de Vico P/1995 S1 (no. 204) -- and which had remained near 8th magnitude since then, had brightened dramatically within the recent past. On the morning that I added Comet Pons-Winnecke I observed this nova during dawn with 10x50 binoculars near magnitude 5 1/2, and on the following morning (when I added the below comet to my tally) I observed it in a darker sky with my naked eye at magnitude 5.3. This is the 42nd nova I have observed during my lifetime (although the first since 2018), and the 6th nova that I have seen with my naked eye.
INITIAL OBSERVATION: 2021 May 9.41 UT, m1 = 13.8, 0.5' coma, DC = 4 (41 cm reflector, 229x)
UPDATE (June 5, 2021): More or less as I expected, Comet Pons-Winnecke brightened fairly rapidly after my initial observation, and was close to magnitude 12 1/2 during the latter part of May (including when I observed it during the lunar eclipse on May 26). Shortly after the beginning of June, however, according to various CCD-based reports the comet underwent a distinct outburst within its inner coma, and some CCD images thereafter (including this one) showed a strinking series of jets and hoods, surrounded by a larger outer coma -- an appearance reminiscent of Comet 156P/Russell-LINEAR (no. 686) when it was brightest during the latter part of last year.
This all happened while there was a bright moon in the morning sky, and furthermore a week-long period of rainy and cloudy weather here in New Mexico prevented me from making any visual observations of the comet. I finally had reasonably clear sky conditions on the morning of June 5, and was somewhat surprised to see that it was only about a half-magnitude brighter than it was when I had last seen it, during the late May eclipse. The bright jet-shaped inner coma so prominent on the CCD images is much more subtle visually, and primarily manifests itself by the fact that the surface brightness of the trailing, or westward, side of the coma is marginally brighter than the leading, or eastward, side. There apepars to be a small, stellar condensation near the apex of this brighter region.
Whether or not the fainter-than-expected appearance of Comet Pons-Winnecke this morning is perhaps due to the outburst already subsiding is something I cannot determine at this time. In any event, in light of the general overall behavior I described above, and the fact that its closest approach to Earth is a week away, the comet may continue to brighten over the next couple of weeks, although at present I don't expect it to get any brighter than about 11th magnitude. The rapidly increasing southerly declination -- -32 degrees by the end of this month -- will start to make observations from my latitude somewhat problematical before too much longer.
MOST RECENT OBSERVATION: 2021 June 5.39 UT, m1 = 11.8, 2.'6 coma, DC = 2 (41 cm reflector, 70x)
One day after first picking up the above comet, I added this one to my tally. Like the previous comet, this is another one that I have seen on previous returns; after obtaining a single observation at a low elevation during the mediocre return in 2002 (no. 304), I observed it again in 2008 (no. 434) during the course of "Countdown," and I discuss its overall history in that entry. It remained at a fairly small elongation throughout its 2008 return, and over the next two months I obtained a handful of observations following my initial one; it never really got much brighter than it was during that first observation.
As I indicated in that "Countdown" entry, Comet Finlay returned again in late 2014 (perihelion in late December), and remained fairly low in the southwestern evening sky throughout its period of visibility. It was around magnitude 12 1/2, close to its expected brightness, when I first picked it up (no. 557) shortly before mid-December, however just over a week later it underwent a distinct outburst, and was around magnitude 9 1/2 according to my measurements. It faded slowly from this, but then, in mid-January 2015 -- three weeks after perihelion passage -- it underwent an even larger outburst, to around 8th magnitude; I could easily detect it with 10x50 binoculars, and it exhibited a distinct telescopic tail close to 15 arcminutes long. I subsequently followed it for the next two months as it slowly faded beyond visual range.
As the comet's 2021 return approached, I noticed that there weren't any reported recovery observations. Starting in mid-February 2021 I began taking occasional sets of images via the Las Cumbres Observatory network, but I was unable to detect any sign of the comet during my first few attempts. Finally, on April 10 I spotted it on three images taken via the LCO facility at Cerro Tololo Inter-American Observatory in Chile, and nine hours later I was able to obtain three additional images of it via the LCO facility at Siding Spring Observatory in New South Wales. Despite distinct trailing of stars on the various images I was able to perform the requisite astrometry and submit this to the Minor Planet Center, and when this was later published, it turns out that these observations were the earliest ones to be reported. Although other observers reported positions as soon as the following day, mine were the first -- which means that, inasmuch as these things are noted, I receive credit for making the recovery!
The astometry software measured an approximate brightness of 17th magnitude for the comet, which is consistent with what I estimated from an examination of the images. The comet was approximately three arcminutes east-northeast of its expected position, and orbital calculations from these images and other post-recovery measurements indicate that its perihelion passage is approximately 1 1/2 hours earlier than what had been predicted; this difference is likely due to the actions of non-gravitational forces.
My recovery images of Comet 15P/Finlay, obtained via the Las Cumbres Observatory network on April 10, 2021. LEFT: 5-minute exposure taken at 8:20 UT from the LCO facility at Cerro Tololo Inter-American Observatory in Chile. The comet is the small "dot" near the center. RIGHT: A "stacked" set of three images (total exposure time 15 minutes) taken near 17:40 UT from the LCO facility at Siding Spring Observatory in New South Wales.
I took a new set of images via the LCO facility at Siding Spring on May 9, and was surprised to see that the comet had brightened dramatically over the course of the previous month. Its appearance on the images inspired me to make a visual attempt the following morning, and despite the fact that it was rather low in my southeastern sky before dawn, I successfully detected it as a diffuse, moderately condensed object slightly brighter than magnitude 13 1/2.
At present Comet Finlay is located near an elongation of 70 degrees, in eastern Aquarius some three degrees northeast of the star Delta Aquarii, and traveling towards the east-northeast at slightly over one degree per day. Since the sun is also currently traveling towards the northeast, the comet will remain low in my eastern sky for the next several weeks, especially since its elongation decreases (to a minimum of 52 degrees near the end of July) and its motion accelerates, to a maximum of 75 arcminutes per day around the time it is nearest Earth (1.09 AU) in mid-June. During this time it travels through Cetus, Pisces, Aries, and Taurus, and at the time of perihelion passage it will be located some six degrees south-southwest of the Pleiades star cluster. The comet remains in Taurus before crossing into Gemini in mid-August; by that time it is north of the sun, thus offering better viewing geometry for the northern hemisphere, and will be traveling just northward of due east (at approximately 50 arcminutes per day) as it reaches its (temporary) maximum northerly declination of +27 degrees in early September. It eventually crosses into Cancer -- where it remains for the next several months -- just before the end of that month.
Under ordinary circumstances I would expect Comet Finlay to reach a peak brightness near 11th magnitude around the time of perihelion passage in July. However, in light of its behavior in 2014 and its rapid recent brightening, it is conceivable that it could become somewhat brighter than that (or, for that matter, fade away between now and then). We'll just have to keep an eye on it and see what it does . . . In any event, barring anything too unusual I expect to be able to follow it until perhaps September or thereabouts.
As is true for many of the other short-period comets that I am observing these days, this is likely the last return during which I will see Comet Finlay. The next return, in 2028 (perihelion early February), is a relatively unfavorable one slightly inferior to that of 2002, and while -- as noted in the comet's "Countdown" entry -- it makes a close approach to Earth (now calculated to be 0.19 AU) in August 2034 during the return after that, whether or not I am actively observing at any level at that time remains to be seen. I highly doubt I will be able to obtain observations during the very close approach to Earth -- now calculated to be 0.041 AU -- in October 2060.
Even though routine recoveries of expected periodic comets are no longer officially recognized, the fact that I was able to make the recovery of Comet Finlay this time around is nevertheless quite special to me. As I recount in the tally entry for Comet 37P/Forbes three years ago, I was able to make a visual recovery of that particular comet during its 1999 return (no. 262), but this recovery of P/Finlay is the first time that I have been able to supply precise positional information for such an event. As I probably continue to decrease my visual observing activities during the coming months and years I will likely increasingly become more active in imaging, and I am hoping to incorporate a significant educational component to this. It is well within the realm of possibility that I might attempt additional periodic comet recoveries in the future, and perhaps get educators and students involved in this particular effort.
INITIAL OBSERVATION: 2021 May 10.44 UT, m1 = 13.3, 0.8' coma, DC = 3 (41 cm reflector, 229x)
Another long-time friend reappears on my tally -- and, like most other recent such additions, quite likely for the last time. As its low periodic comet number indicates, it was one of the earliest-known short-period comets, being discovered in November 1843 by French astronomer Herve Faye from Paris Observatory. Around that time it was faintly visible to the unaided eye near 6th magnitude, this brightness perhaps being due to an outburst that conceivably could have been triggered by a moderately close approach to Jupiter 2 1/2 years earlier. Faye's comet was found to be traveling in an orbit with an approximate period of 7 1/2 years, and there have only been relatively minor fluctuations in its orbital period and perihelion distance since then. While it has never been as bright as it was on its discovery return, it has nevertheless been a moderately easy telescopic object during most of its subsequent returns, and except for the returns of 1903 and 1918 when it was badly placed for observation, it has been recovered on every return since its discovery. The current return is the 23rd during which it has been observed.
Comet Faye has been around with me ever since I first started following comets. It had a favorable return in late 1969, and although this was a little too early for me to attempt any observations, I nevertheless read about it in publications at the time. It returned again under somewhat mediocre geometric conditions in early 1977, and in significant part due to this being during my freshman, or "plebe," year at the U.S. Naval Academy I again didn't attempt any observations. The comet had another mediocre return in mid-1984 and I did successfully observe it then (no. 69); a most remarkable event occurred during this return when my friend and colleague Charles Morris made a visual recovery (at my suggestion), a very rare occurrence in this day and age. (It turned out that the comet had already been recovered at Palomar by Jim Gibson two weeks earlier, but this hadn't yet been announced, so Charles did receive credit for his recovery.) It remained low in the eastern morning sky during that return and never got brighter than about magnitude 12 1/2, and I obtained only a handful of observations of it.
Comet Faye had a very favorable return in late 1991, and I followed it (no. 163) for over six months as it reached a peak brightness of magnitude 9 1/2 and I could faintly detect it with 10x50 binoculars. The 1999 return was very unfavorable, but I nevertheless was able to obtain a single observation of it (no. 259) as a very faint object 4 1/2 months before perihelion passage. The following return, in 2006, was another very favorable one almost identical to that of 1991, although an approach to Jupiter during the interim had increased the perihelion distance somewhat and thus it didn't quite get as bright; I followed it for almost seven months (no. 393) and it reached 10th magnitude. The return in 2014 was very unfavorable, and although I attempted it on a few occasions, I never succeeded in observing it that time around.
An approach to Jupiter (0.63 AU) on my 60th birthday (March 7, 2018) decreased the perihelion distance by about 0.04 AU. On its present return it was recovered on March 26, 2021 by German astronomer Bernd Lutkenhoner with the Slooh Observatory facility at La Dehesa, Chile, at which time he reported it as being around 16th magnitude. Various reports I've read and images I've seen have indicated that it has brightened steadily since then, and a series of images I took via the Las Cumbres Observatory network on June 16 suggested it was bright enough to attempt visually. Two mornings later I successfully observed it as a small and somewhat condensed object near magnitude 13 1/2.
Although not quite as favorable as those of 1991 and 2006, this year's return is still a moderately good one. At present it is in the morning sky at an elongation of 64 degrees and located in eastern Pisces some three degrees south of the star Eta Piscium; it is traveling towards the east-northeast at 40 arcminutes per day, and over the next two months it crosses through Aries and Taurus (curving gradually more directly eastward) while passing some five degrees south of the Pleiades star cluster shortly before mid-August and through the northern extremities of the Hyades star cluster two weeks later -- at which time it is at its farthest north point (declination +19 degrees). Now traveling due eastward but gradually curving more towards the south, Comet Faye crosses into northeastern Orion in late September, into southwestern Gemini in mid-October, and then into Monoceros just before the end of that month. It passes through its stationary point during the latter part of November when it will be located some four degrees east-southeast of the star cluster NGC 2264; thereafter it reaches a minimum southerly declination of +7 degrees shortly after mid-December and begins traveling westward, and is at opposition just before the end of the month (and year) when it will be located two degrees north of the star cluster NGC 2244 and the Rosette Nebula (NGC 2237). The comet then begins traveling towards the northwest, crossing back into Orion just after mid-January 2022 and passing through its other stationary point at the beginning of February.
Comet Faye should continue brightening steadily as it approaches perihelion, and will probably reach a maximum brightness near 11th magnitude during September and October. It will likely have faded by perhaps a magnitude or so by the time it is nearest Earth (0.94 AU) in early December, and thereafter will probably fade more rapidly; I will likely lose it by late December or early January.
The comet's next return, in 2029 (perihelion early March) is unfavorable, while the return after that, in 2036 (perihelion early September) is essentially identical to this year's; as I've indicated in previous entries, however, I will likely be finished with visual comet observing well before then. After additional alternating between favorable and unfavorable returns, the comet passes 0.5 AU from Jupiter in 2076 which will drop its perihelion distance down to just over 1.5 AU, and set the stage for the closest approach it will have made to the Earth in several centuries -- 0.57 AU -- shortly after the beginning of the 22nd Century. I will leave observations of Comet Faye at all these future returns to observers of future generations.
Now that the coronavirus pandemic is receding, things are slowly starting to revert back to normal, although the new "normal" will likely be somewhat different from the old one. The Governor of New Mexico just announced a couple of days ago that our State will fully reopen on July 1, now less than two weeks away. On the home front, I met by grandson Ethan for the first time a month ago; being born several weeks premature he was still small for his age, but at least he is out of the hospital and is home now, and hopefully will grow into a healthy young man during the years to come.
One interesting recent personal event involves the "Ice and Stone 2020" program that I conducted throughout last year. While putting together the program two years ago, on June 6, 2019, I took some images of "my" asteroid, (4151) Alanhale, to utilize as an illustration of how asteroids move against a background star field. I showed two images, taken two hours apart, to my partner Vickie to see if she could spot the moving asteroid; she didn't . . . but, she managed to spot another asteroid (that I was unaware of) in the same star field! Some research showed that this was (75591) 2000 AN18, which had been discovered by the LINEAR program here in New Mexico in January 2000. In light of the rather interesting circumstances involved, and since in a sense Vickie had "re-discovered" this asteroid, I submitted a request to the IAU's Working Group on Small Body Nomenclature to have it named after her. The entire asteroid-naming process has undergone some delays in the recent past, and it took two years before things began to get back on track, but I was informed a month ago that my request would be approved; just a few days ago the WGSBN formally announced (among quite a few other asteroids' names) the naming of asteroid (75591) Stonemose. (I have the annotated images posted as a part of the I&S20 presentation on "Main Belt Asteroids;" Alanhale is indicated by the blue arrows, Stonemose by the yellow arrows.) The two asteroids are unrelated to each other and are traveling in different orbits, and it was only a coincidence that they happened to be passing by each other -- at different distances from Earth -- for a few hours right at the same time I was taking the images. Vickie and I, meanwhile, have been together for four years now, and I am hoping that that remains true for however long this life lasts.
INITIAL OBSERVATION: 2021 June 18.42 UT, m1 = 13.4, 0.5' coma, DC = 3 (41 cm reflector, 70x)
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