TALLY ENTRIES 641-650
|641. COMET LEMMON C/2018 EF9 Perihelion: 2018 May 23.13, q = 1.557 AU
I have to confess, the addition of this comet to my tally comes as a surprise. It was initially discovered on March 9, 2018, by Alex Gibbs during the course of the Mt. Lemmon survey in Arizona as a very faint object of 21st magnitude; despite the fact it has been found to be moving in an orbit reminicent of a long period comet (eccentricity 0.9985, inclination 85 degrees) it appeared entirely asteroidal, and was announced as an asteroid with the designation 2018 EF9. It wasn't until a month later that infrared images obtained by the NEOWISE mission revealed very weak cometary activity, which was subsequently confirmed by visible-light images taken by large ground-based telescopes, and it was then re-announced as a comet.
Even after its cometary nature was realized, it was never expected to become bright, indeed, ephemeris predictions never had it getting any brighter than about 19th magnitude. However, a few days ago Austrian comet photographer Michael Jager (whom we have encountered in previous tally entries, most notably in connection with the comet he discovered) reported that, in recent images he had taken, the comet was accompanied by a somewhat large coma and was distinctly brighter than expected. Armed with this information, I made a visual attempt on the evening of May 13 and, sure enough, successfully detected the comet as a very weak, vague, "soft" object of magnitude 13 1/2. I observed it again on each of the next two nights, with the appearance basically unchanged (although it was perhaps just slightly fainter).
The comet is currently located in far northern circumpolar skies, at a declination of +85 degrees in northwestern Camelopardalis. For the time being it is traveling towards the southwest at aboout 10 arcminutes per day (crossing into Cepheus shortly before the end of May), however upon reaching a minimum declination of +84 degrees in early June -- at which time it is in conjunction with the sun, 61 degrees north of it -- it turns northward, to reach a maximum declination of +86 degrees in early July before turning back southward, dropping south of declination +80 degrees in early August and crossing into eastern Draco in the middle of that month. As far as its brightness is concerned, that's a bit problematical; while it is still a few days away from perihelion, it already was closest to Earth (1.05 AU) in early March, and although after reaching a (temporary) maximum geocentric distance of 1.82 AU in late June it then starts approaching again, by then it will be well past perihelion. Unless there is a resurgence of activity, I doubt if I will be following this comet for very long.
Comet Lemmon seems to be an example of a type of object that we're seeing more and more of as the surveys become ever more expansive: an evolved, essentially inert object that becomes a weakly active "asteroid-turned-comet" when near perihelion, exhibiting at most a vague, weak coma that disperses within a relatively short period of time. (For what it's worth, Comet Lemmon has returned at least once before, approximately 11,000 years ago.) I've observed a handful of these comets over the past few years, and in fact there is another recently-discovered object that may be yet another example, and which I theoretically may observe within the not-too-distant future.
The attentive reader may have noticed that I have changed the name of the banner headline on these tally pages. This is a part of the current refocusing I am doing with Earthrise, and despite what may be the initial impression it actually reflects a de-emphasizing of the importance of my visual comet tally as I expand the overall program. I will have more to say about this in future entries and in future announcements.
INITIAL OBSERVATION: 2018 May 14.19 UT, m1 = 13.6, 1.3' coma, DC = 1 (41 cm reflector, 229x)
UPDATE (June 11, 2017): I was unable to convince myself I was seeing this comet when I attempted it a few nights ago, my first attempt of the current dark run. It appears that the weak coma I observed -- perhaps produced as a result of an outburst -- has just about dissipated. This appearance is consistent with recent CCD images of this comet that I have seen, and overall this behavior is consistent with that of some of the other recent "asteroids-turned-comets" that I have observed.
I have been eagerly awaiting this particular comet. It's an old friend that has a fascinating observational history, and it has also been around for some interesting events in my personal life; I recount all of this in its "Countdown" entry for its previous return in 2012 (no. 497). As I also indicate in that entry, this year's return of the comet is the best of the entire 21st Century; furthermore, my life is in the midst of some interesting goings-on that make a return at this time rather appropriate. Since, more than likely, this is the last return at which I will observe this comet, it seems only fitting that it go out with a "bang!"
The comet's "Countdown" entry mentions that this year's return is very similar to my first observed return of it, the one in 1985 (no. 82) -- indeed, the respective perihelion dates are only five days apart. On its way in this time it was recovered on February 12, 2018, by Japanese amateur astronomer Toshihiko Ikemura (incidentally, a co-discoverer of Comet 76P/West-Kohoutek-Ikemura, which I observed on its discovery return in 1975 (no. 15) and again in 1993 (no. 182)). Since that time it has brightened slowly as it has traveled northward along the Aquila-Cygnus region of the Milky Way, and by early May it had reached the point where visual attempts seemed worthwhile. My first couple of attempts were unsuccessful -- although I did successfully image it with the Las Cumbres telescopes -- and then finally, on the morning of May 24, I was able to detect it as an extremely faint, very small, moderately condensed object slightly fainter than 14th magnitude, that exhibited the expected motion over the course of half an hour.
At present the comet is located in southeastern Cygnus and is traveling towards the northeast -- roughly parallel to the galactic equator, thus remaining within rich Milky Way star fields -- at somewhat under 40 arcminutes per day, although this increases over time. It passes just to the east of the North America Nebula (NGC 7000) around the time of the June Solstice -- at which time it should be between 11th and 12th magnitudes, based upon its brightness in 1985 -- then goes north of declination +50 degrees at the beginning of July before crossing into southern Cepheus and entering northern circumpolar skies by the middle of that month. Around that time it should be near 9th or 10th magnitude -- and thus starting to become visible with binoculars -- and it should also begin exhibiting a rather distinct dust tail visually.
By the end of July Comet 21P will have entered western Cassiopeia, and it will be traveling just northward of due east at almost one degree per day. It reaches its maximum northerly declination (+66.5 degrees) on August 6, at which time it will be several degrees north of the "W," and after that it begins descending rapidly towards the southeast through Camelopardalis, continuing to parallel the galactic equator as it does so. During the latter part of August the comet should be close to 7th magnitude, and at a similar point in 1985 I could detect a bright one-degree-long dust tail even with relatively small binoculars.
Around the beginning of September the comet crosses into northwestern Auriga, and it passes one degree to the southwest of the bright star Capella on September 3. When at perihelion -- at which time it is also closest to Earth (0.39 AU) -- it will be passing 15 arcminutes west of the star cluster M37, and will be traveling southeastward at almost two degrees per day. Within a few days it crosses into southwestern Gemini and on the 15th it passes directly over the star cluster M35, before crossing into Monoceros just over a week later. By the end of September the comet will likely have faded to somewhere between 8th and 9th magnitudes.
Although Comet 21P should remain visually detectable for some time thereafter, with its continued receding from the earth and the sun, and thus continued fading, the rest of the apparition is somewhat anti-climactic, especially for those of us in the northern hemisphere as it continues its southward trek. After passing half a degree east of the star cluster M50 on October 7 it crosses into Canis Major three days later, and reaches its stationary point in early November when it will be located half a degree east of the star Eta Canis Majoris (Aludra); by this time it will likely be no brighter than 10th or 11th magnitude. The comet crosses into Puppis a few days later, is at its maximum southerly declination (-39.7 degrees) during the second week of December, crosses into Columba a week later, and is at opposition a week after that -- just before the end of 2018 -- but it will probably fade from view sometime during this time.
In this comet's "Countdown" entry I discussed its association with the Draconid meteor shower, which is normally quite weak, but which has produced some strong historical displays, particularly in years during which the comet has passed perihelion. Some predictions I read several years ago suggested that the conditions for a strong Draconid shower this year were relatively good, however more recent predictions I've read suggest that this probably will not happen, although there might be some enhanced activity. It is always possible, of course, that a surprise strong -- and likely brief -- shower might nevertheless occur. The Draconids peak on the night of October 8-9, and as it happens that date coincides with new moon this year, so (weather permitting) we should at least have dark sky conditions for whatever display does occur.
I have already discussed the striking similarities between this year's return of P/Giacobini-Zinner and that of 1985. For me personally, the similarities extend to my first observations of the respective returns: in 1985 I added it while attending the Riverside Telescope Maker's Conference near Big Bear, California -- a gathering I attended most of the years when I was living in southern California, although this was the only comet I added to my tally from there. My adding of the comet to my tally this year -- which took place just two calendar days before the respective date in 1985 -- occurred on the very morning when I departed New Mexico to attend that very same gathering -- my first time in over 20 years. I was a guest speaker at this year's gathering, and I was able to announce my observation during my talk.
A lot happened in both my professional and my personal lives during the comet's 1985 return. Right around the time I first saw the comet I was transferred to the Radio Science group of the Deep Space Network at the Jet Propulsion Laboratory where I was working at the time, and just a month later I was an active participant in the Vega 1 and 2 "Venus Balloon" encounters at Venus. After that I began preparing for the Voyager 2 encounter with Uranus a few months later. In September Comet 21P became the first comet to be encountered by an artificial spacecraft, and although I wasn't directly involved in that event, I "witnessed" it from the Space Flight Operations Facility at the Lab. Meanwhile, in my personal life I got married during the course of the comet's return that year, and my "bachelor party," as it were, involved observing comets (including both this comet and the inbound Comet 1P/Halley 1982i (no. 85)) with some astronomical friends of mine in the mountains east of San Diego.
As I mentioned above, there are some interesting things taking place in my life now as this comet once again makes a visit. For the past several weeks I have been busy putting together the educational program that I discuss in my recent statement, and I have started to fundraise to get the project going in earnest -- indeed, this was my primary goal in attending the recent Riverside gathering. In June I will be presenting to several hundred university students who will be attending the Spaceport America Cup. There aren't any spacecraft encounters with comets taking place now, but there are several notable comets (both long-period and short-period) that will be passing perihelion later this year, that along with this comet will be the focus of the educational efforts I plan to be doing. Meanwhile, while there doesn't seem to be any wedding bells anytime in my future -- and thus observing this comet is rather unlikely to be a part of any future "bachelor party" -- I do have a new ladyfriend, Vickie, whom I've mentioned in a couple of previous entries, and whom I've been seeing for a little over a year now and who accompanied me (and indeed was a big help) during my recent trip to California.
I also note, for whatever it's worth, that this year's perihelion passage of Comet Giacobini-Zinner takes place one day after what would have been my late father's 100th birthday.
|I stated at the outset that this will probably be my last observed return of P/Giacobini-Zinner. The return in 2025 (perihelion late March) is very unfavorable and there is no possibility of my seeing it, however the subsequent return in 2031 is quite similar to this year's return and the one in 1985 -- the perihelion date is only five days earlier than 1985's and ten days earlier than this year's. An approach to Jupiter (0.37 AU) in February 2029 will increase the perihelion distance to 1.07 AU and thus the comet will be slightly farther from the sun and Earth in 2031 than it is this year, but otherwise the viewing geometry is quite favorable. However, this is well after the "retirement" time frame that I have discussed elsewhere, and while this may well be one of those "I'll cross that bridge when I get there" items, I am nevertheless going to treat this year's return as if it is going to be my last.|
|Comet 21P/Giacobini-Zinner on May 23, 2018 (one day before I picked it up visually), as imaged by the Las Cumbres Observatory facility at Cerro Tololo Inter-American Observatory in Chile.|
INITIAL OBSERVATION: 2018 May 24.42 UT, m1 = 14.3, 0.3' coma, DC = 4 (41 cm reflector, 229x)
Thus far, 2018 has been a relatively quiet year for comets, especially bright ones; indeed, it has been almost eleven months since I have been able to view a comet with binoculars. There are several inbound comets, including the previous entry as well as others I discuss on the "incoming comets" page, that will change this state of affairs within the not-too-distant future; meanwhile, there are also several fainter comets I will likely be observing as well. One of those is this object, which was originally discovered in February 2013 by the Pan-STARRS program in Hawaii; at that time it appeared entirely stellar, with a calculated orbital period now known to be 4.9 years, and it was assigned the asteroidal designation 2013 CU129. Four months later it began to exhibit a distinct tail, and it was re-announced as a comet. After passing perihelion in early August of that year it passed 0.62 AU from Earth in mid-September, and it was a rather impressive sight in some of the CCD images that were taken around that time, but despite several attempts I never was able to convince myself I was detecting it visually.
On its present return the comet was recovered on January 12, 2018, by the Mt. Lemmon survey in Arizona, and independently four days later by German amateur astronomer Edwin Schwab utilizing a remotely-controlled telescope at Calar Alto Observatory in Spain. Initially, it was quite faint (20th magnitude) and appeared entirely asteroidal, however by about mid-April it was once again beginning to exhibit a distinct tail in CCD images. I made one unsuccessful visual attempt for it in mid-May -- although I did successfully record it with the Las Cumbres Observatory network -- and then on the first night of the current dark run, i.e., the evening of May 31, I successfully observed it as a very faint (slightly fainter than 14th magnitude), tiny, and somewhat condensed object that exhibited the expected motion during the half-hour I was able to follow it before moonlight from the rising bright moon began to interfere. It appeared marginally brighter when I observed it again four nights later, but despite the tail's relative prominence on images I have not been able to detect this visually.
The viewing geometry at the present return is somewhat better than that in 2013, with a minimum distance from Earth of 0.24 AU taking place shortly after mid-July. Currently the comet is an evening sky object, being located in southern Cancer, but since it is already south of the sun and is traveling almost due southward at 40 arcminutes per day (which is increasing) those of us in the northern hemisphere will lose it before long, although it should remain accessible for observers in the southern hemisphere for at least another couple of weeks. It passes one degree east of the star cluster M67 on June 13, and a week later crosses into western Hydra, passing through the "head" of that constellation and subsequently passing just over half a degree east of the star cluster M48 on July 1. By this time the comet is rapidly shifting its motion towards the south-southwest, traveling at 90 arcminutes per day at the beginning of July and two degrees per day during the middle of that month when it is nearest Earth. It is in conjunction with the sun (39 degrees south of it) on July 11, at which time it will be in Puppis between the star clusters M46 and M47; while it may not be too easy to access, since it will be between the earth and the sun there is some potential for brightness enhancement (especially with the dust tail) via forward scattering of sunlight.
By the latter part of July Comet 364P will have emerged into the morning sky, although since it will be near a declination of -30 degrees it initially remains exclusively visible from the southern hemisphere. It travels rapidly westward through Columba, Caelum, and Eridanus, and enters Fornax during the second week of August; between August 8 and 10 it travels directly across the Fornax cluster of galaxies, and it passes less than 20 arcminutes south of the Fornax Dwarf Galaxy on August 18. By the second week of August the elongation will have increased to the point where the comet is again accessible to the observers in the northern hemisphere. The brightness at this time is difficult to predict, but perhaps 12th or 13th magnitude is not unreasonable. Meanwhile, after reaching a peak southerly declination of -35 degrees in early August the comet begins a gradual turning northward, crossing into Sculptor at the end of that month, being at opposition shortly after the September equinox, and crossing into Aquarius in early October. By that time it will likely have faded beyond the range of visual detectability.
|The comet's next return, in 2023 (perihelion mid-May) is even better than this year's, with a minimum distance from Earth of only 0.12 AU taking place in early April. Since this occurs on the inbound leg towards perihelion, we observers in the northern hemisphere will get the better end of the deal that time, when the comet will be conveniently placed in the morning sky and conceivably as bright as 11th or 12th magnitude. It may still be visually detectable at the following return in 2028 (perihelion late April), when it passes 0.50 AU from Earth in mid-March. After that the comet stays relatively far from Earth for quite some time; it eventually will make a couple of close approaches to our planet in the 2070s (following an approach to Jupiter (0.72 AU) in 2060 that will shorten the orbital period and perihelion distance to 4.8 years and 0.77 AU, respectively), but of course I expect that, for a variety of reasons, my days of comet observing will be long over by then.|
|Comet 364P/PANSTARRS on June 4, 2018, as imaged by the Las Cumbres Observatory facility at Cerro Tololo Inter-American Observatory in Chile.|
INITIAL OBSERVATION: 2018 June 1.16 UT, m1 = 14.3, 0.3' coma, DC = 4-5 (41 cm reflector, 229x)
Another dim comet joins my tally. Unlike the previous entry, however, which is a somewhat interesting short-period comet, this is another one of those nondescript, large-q long-period comets that show up on my tally with a fair amount of regularity, especially after the advent of the comprehensive sky surveys two decades ago. It was discovered back on June 21, 2017 with the Mauna Loa telescope during the course of the ATLAS survey in Hawaii; since going on-line in 2015 ATLAS has now discovered an even dozen comets, of which I have now seen two (the first being Comet Heinze C/2017 T1 (no. 634)). This is the first comet I have seen which carries the name "ATLAS."
This Comet ATLAS is traveling in a relatively steeply inclined retrograde orbit (inclination 106 degrees) and at the time of its discovery was located in northern circumpolar skies 6.05 AU from the sun and 6.16 AU from Earth. After being in conjunction with the sun (albeit some 63 degrees north of it) in early January 2018 it began emerging into the morning sky over the next couple of months, and some of the images I saw and reports I read suggested it might be worth looking for visually. I made a couple of unsuccessful attempts for it during May, although I did successfully record it with the Las Cumbres Observatory network, and the comet's brightness on the image suggested I wasn't missing it by much. Finally, on my first attempt of the current dark run, i.e., on the evening of June 4, I successfully detected it as a very faint, small, and relatively condensed object slightly brighter than 14th magnitude. It exhibited a similar appearance although, curiously, it appeared marginally fainter, when I observed it again a few nights later.
The comet is currently located in northwestern Lyra and is traveling towards the west-southwest at slightly over 20 arcminutes per day; in a few days it crosses into Hercules (where it remains for the next several months as its motion turns more and more southerly) and it is at opposition right around the time of the June solstice. It is at its stationary point in mid-September (when it will be located a couple of degrees northwest of the star Omega Herculis) and it remains accessible in the evening sky until around the latter part of October. Throughout this time the comet will likely remain faint, brightening perhaps a half-magnitude or so at most.
After being in conjunction with the sun at the end of November the comet begins to emerge into the morning sky by the latter part of January 2019, at which time it will be located a few degrees east of the star Eta Ophiuchi ("Sabik"). It continues its general southward motion, being at its stationary point at the end of February when it will be traversing some of the dust clouds in southern Ophiuchus a couple of degrees east of the star Xi Ophiuchi. After that Comet ATLAS travels southwestward through Ophiuchus, then crosses into Scorpius in early May and into Lupus a month later; it is closest to Earth (2.48 AU) in mid-May around the same time it is at opposition, at which time it also crosses south of declination -40 degrees. Throughout this entire period the comet will likely be around its brightest, probably somewhere between 12th and 13th magnitudes.
After that the rest of the comet's apparition is rather anti-climactic, especially for those of us in the northern hemisphere, as it remains south of declination -40 degrees (although it temporarily reaches a minimum southerly declination of -43 degrees in mid-June). It travels westward through Lupus and Centaurus and is at its stationary point shortly after mid-August, at which time it will be located just 1 1/2 degrees east of the bright galaxy NGC 5128 ("Centaurus A"). It travels towards the south-southeast after that and enters southern circumpolar skies by late December, but will have almost have certainly faded beyond the range of visual detectability well before then.
INITIAL OBSERVATION: 2018 June 5.24 UT, m1 = 13.8, 0.3' coma, DC = 4 (41 cm reflector, 229x)
|UPDATE (March 4, 2019): Following its conjunction with the sun in late 2018, Comet ATLAS began emerging into the morning sky in early 2019, and I successfully picked it up in early March as a small and relatively condensed object of magnitude 13 1/2, slightly brighter than it appeared the previous year but somewhat fainter than the above scenario predicted. It is currently traveling almost due southward through rich Milky Way star fields in southeastern Ophiuchus, about 2 1/2 degrees east-southeast of the star Xi Ophiuchi (and, curiously, two degrees northeast of Jupiter); it is in the process of making its turn towards the southwest and passes just 40 arcminutes southeast of Jupiter on March 10. I expect at most just a marginal brightening over the coming few weeks, and since it is running fainter than expected I suspect I may be able to follow it up until the time of opposition two months from now but probably not much beyond that.|
|Cropped 5-minute exposure of Comet ATLAS C/2017 M4 obtained March 3, 2019 with the Las Cumbres Observatory facility at Siding Spring Observatory in New South Wales.|
|MOST RECENT OBSERVATION: 2019 March 2.50 UT, m1 = 13.6, 0.7' coma, DC = 4 (41 cm reflector, 229x)
Another ATLAS comet . . . This one was discovered on May 25, 2018, by Henry Weiland utilizing the ATLAS Mauna Loa telescope. It was located in eastern Sagittarius and traveling rapidly westward; meanwhile, the various reported brightness measurements were rather discordant, with the discovery team reporting the comet as being 17th magnitude and other observers even fainter at 18th magnitude, however other observers were reporting it as being as bright as 15th, even 14th, magnitude. Once a reliable orbit was calculated -- which included prediscovery images in data taken by Pan-STARRS back in November 2017 -- it was found that Comet Weiland was almost two months past perihelion passage and is traveling in a shallow-inclined retrograde orbit (i = 164 degrees, i.e., a retrograde orbit inclined only 16 degrees with respect to the ecliptic). Comet Weiland was also found to be of Halley-type, with an orbital period of 163 years.
Once the moon cleared from the sky enough for me to make observation attempts, I was still unable to look for the comet due to several nights of cloudy and rainy weather -- an early, brief "monsoon" season. It was just as well, for during this time it was traveling through some extremely dense and rich star fields in the Sagittarius Milky Way; some of these are so dense that they create an almost continuous "carpet" of dim background stars that offers very little contrast with a diffuse comet that might be moving through. I finally had a clear night on the evening of June 10, when the comet was located in southeastern Ophiuchus and fortuitously situated in front of a small dust cloud, and I have to admit I was a bit surprised when I clearly saw a very pale and diffuse object, near magnitude 13 1/2, that exhibited the expected motion over the next twenty minutes. Two nights later, when the comet was passing by the globular star cluster NGC 6325, I was once again able to follow it for about half an hour as it traveled against the background stars, appearing as little more than a pale, ghostly "presence."
Comet Weiland is traveling rapidly (currently 100 arcminutes per day) to the west-northwest across Ophiuchus, crossing into northern Scorpius on June 21 and passing just north of the "head" of that constellation three days later. It was closest to Earth (1.02 AU) on June 9 and at opposition three days later, and I accordingly expect a rather rapid fading during the coming weeks. The two observations I currently have of it may well be the only ones I obtain, since as I write these words another round of monsoon activity -- due in no small part to the remnant of Hurricane Bud, which should be moving through the area -- is beginning, which is expected to last for most of the next week. While I may possibly look for the comet again if I get another clear night in the not-too-distant future, more than likely I am already done with it.
INITIAL OBSERVATION: 2018 June 11.24 UT, m1 = 13.4, 1.2' coma, DC = 0-1 (41 cm reflector, 229x)
I visually attempted this comet, unsuccessfully, on three consecutive returns before finally succeeding on the fourth return, in 2011 (no. 491), near the end of "Countdown." I discuss all this, as well as the comet's overall observational history, in its "Countdown" entry; I also discuss there that an approach to Jupiter on the outbound leg of its orbit would decrease both the comet's perihelion distance and its orbital period, and as a result of this its 2018 return is the most favorable return it has had since its original discovery in 1949. It was imaged by the Pan-STARRS program in Hawaii during January 2015, only 2 1/2 months before aphelion, and thus can now be considered an "annual" comet; the first post-aphelic observations were obtained -- again by Pan-STARRS -- on March 10, 2016, eleven months after aphelion.
On Comet Johnson's present return I successfully picked it up on my first attempt, on the morning of June 20; it appeared as a small, moderately condensed object of 14th magnitude. It is presently located in southern Aquarius some five degrees southeast of the star Iota Aquarii (and just 50 arcminutes northwest of the solar-type binary star 53 Aquarii, one of my favorite stars from my Ph.D. thesis, as I was the first person to calculate and publish an orbit for it, an orbit which still stands a quarter-century later); it is traveling in a generally southeasterly direction across that constellation (passing half a degree north of 53 Aquarii on June 28), gradually turning more and more southward until it is at its stationary point in early August, three degrees south of the star 66 Aquarii. Now traveling towards the south-southwest, it passes through perihelion on August 12, crosses into northeastern Piscis Austrinus on August 18, is nearest Earth (1.014 AU) on August 21, and is at opposition at the end of August (at which time it is one degree west of the star Epsilon Piscis Austrini); throughout this entire time the comet should be near a peak brightness of 13th magnitude. Afterwards, it reaches its maximum southerly declination (-28.8 degrees) on September 24, is at its stationary point three days later (after which it resumes direct, or eastward, motion), again passes one degree west of Epsilon Piscis Austrini on October 25, and crosses back into Aquarius on November 4. I expect that it will fade beyond the range of visual detectability sometime during this period.
As I continue the re-engagement of Earthrise that I have discussed elsewhere on this site and in previous entries, I continue to grow busier with Earthrise-related activities. One recent example involves Spaceport America; I was rather heavily involved in the initial development of the Spaceport for quite a number of years after completing graduate school, however that connection has lapsed in recent years as I have dealt with all the personal goings-on that I have recounted elsewhere. Just recently, however, I have been able to re-establish connections with the Spaceport, and as a result I was invited to speak to students who were participating in the Spaceport America Cup late last week. It was a delight and an honor to speak with and engage with such talented and dedicated students, and I was especially heartened by the overall international flavor of the event, as there were students from quite a few different countries. I hope to continue and grow this re-established connection to the Spaceport during the years to come, as a part of the overall continuing re-engagement of Earthrise. This is, after all, what Earthrise is all about.
INITIAL OBSERVATION: 2018 June 20.41 UT, m1 = 13.9, 0.3' coma, DC = 4 (41 cm reflector, 229x)
Ever since its discovery by the Pan-STARRS program back on September 23, 2017, we've never been quite sure what to expect from this comet. The very small perihelion distance called attention to the comet right away, suggesting the possibility that it could become quite bright; countering this, on the other hand, was the fact that the comet's brightness at the time of its discovery was very faint (21st magnitude). Furthermore, calculations soon indicated that this is likely a first-time visitor from the Oort Cloud, and such objects tend to under-perform compared to their counterparts that have been around the sun previously.
Comet PANSTARRS is traveling in steeply-inclined retrograde orbit (inclination 99 degrees) and was in northern circumpolar skies (declination +74 degrees) at the time of its discovery; it has remained in northern circumpolar skies ever since, although it has gradually traveled southward. By the time it disappeared into conjunction with the sun in mid-January 2018 it had only brightened by, at most, a magnitude, which did not bode well for a bright display later on. Fortunately, by the time it re-emerged back into the morning sky two months later it had brightened by an additional one to two magnitudes, and it has continued to brighten slowly and steadily since that point. Beginning in June I started submitting image requests via the Las Cumbres Observatory network, and although some of these images did indeed show the comet, it appeared only as a very faint object close to the images' limiting brightness. I also made a couple of visual attempts during June, but these were unsuccessful.
According to various images I've seen and reports I've read, right around the time of the full moon in late June Comet PANSTARRS underwent a distinct increase in brightness, although unfortunately because of the bright moonlight as well as the onset of monsoon activity here in New Mexico I was unable to make any visual attempts. Then, on the morning of July 1 Austrian amateur astronomer and comet imager Michael Jaeger -- whom we have encountered before in these pages -- reported that the comet had brightened dramatically over the previous 24 hours. Fortunately we had a brief break from the monsoon activity that night, and on the following morning -- July 2 -- despite the bright moonlight I could easily detect the comet as a slightly condensed object of 10th magnitude. Some observers located at more northerly latitudes, who were able to access the comet in the evening sky before moonrise, reported it as being up to half a magnitude brighter, and I suspect these reports are closer to "reality."
The comet is currently located in western Camelopardalis, and for the time being is traveling almost due eastward at about 45 arcminutes per day. This motion gradually turns more and more southward over the next few weeks and accelerates, and when the comet crosses into northern Auriga on July 20 its motion will have increased to 80 arcminutes per day. It will still be within that constellation on August 1, by which time its motion will be almost directly to the southeast at close to 3 degrees per day, and its elongation will have dropped to 31 degrees. A couple of days later the comet crosses into Gemini, and on the 4th and 5th it passes just west of the stars Castor, then Pollux (passing almost directly over Pollux late on the UT date of the 5th); by this time the elongation will have decreased to 21 degrees and the rate of motion will have increased to 3 1/2 degrees per day. The comet is closest to Earth (0.76 AU) on August 6, and will quickly thereafter will be lost in sunlight. It passes over to the far side of the sun (as seen from Earth) after perihelion, and begins re-emerging into the morning sky around the beginning of November.
The big question, certainly, is what to expect in terms of the comet's brightness and overall display, and a lot of that depends upon the significance of the recent upsurge in brightness. If it brightens somewhat "normally" from this point, we are perhaps looking at dim naked-eye brightness (5th to 6th magnitude) during the latter part of July, and perhaps as bright as 3rd to 4th magnitude when it makes its passage by Castor and Pollux in early August. On the other hand, it this is a major outburst that marks the comet's "last hurrah," then it may disintegrate completely by the time it reaches perihelion. We'll just have to wait and see . . . For what it's worth, the geometry is good for forward scattering of sunlight in early August, which would enhance the brightness of a dusty coma and dust tail, however indications thus far indicate a gassy and rather dust-poor comet.
Unfortunately, the earliest indications at this time are not favorable. I've read reports that the coma is already growing diffuse and fading out, suggesting that this may have indeed been a "last hurrah." I have not yet had a chance to verify (or dis-confirm) these reports, but hopefully I'll have an opportunity to do so within the not-too-distant future.
Although I rather strongly doubt that this will happen, it is at least conceivable that Comet PANSTARRS could briefly reach "Great Comet" status. The northern hemisphere has not had a "Great Comet" since 1997 (the appearance of Comet Hale-Bopp C/1995 O1 (no. 199)), although -- in what seems to me to be a bit of unfairness -- the southern hemisphere has had two such objects since then: Comet McNaught C/2006 P1 (no. 395) which I was nevertheless able to view telescopically during the daytime when near perihelion, and Comet Lovejoy C/2011 W3 (no. 500) which was nothing but a ghost by the time I was able to view it. There have been a couple of comets that had the potential to be northern hemisphere "Great Comets" during this time but which fizzled away; the most notorious example has been Comet ISON C/2012 S1 (no. 529) in late 2013. Seeing at least one more "Great Comet" is one of the items on my "bucket list" before the "retirement" that I have discussed elsewhere on these pages, but of course that depends on what comets might be on their way in at this time. It is possible that Comet PANSTARRS C/2017 K2 could become a "Great Comet" when near perihelion in late 2022, although, once again, it will only be visible from the southern hemisphere at the time. I suppose I could briefly come "out of retirement" to view the next "Great Comet" if that's the way things eventually turn out.
INITIAL OBSERVATION: 2018 July 2.39 UT, m1 = 10.0, 1.6' coma, DC= 2-3 (41 cm reflector, 70x; moonlight)
UPDATE (July 19, 2018): Following my initial sighting of this comet, the summer monsoon struck with a vengeance here in southern New Mexico: almost two solid weeks of rain and clouds. According to my colleagues around the world who were keeping a watchful eye on the comet during the meantime, the coma began to fade and disperse, and it looked like the comet might indeed be disintegrating, and that there would be little, if anything, left of it by the time it reached perihelion.
And then, on July 15, Michael Jaeger reported that the comet had undergone a second, and much stronger, upsurge in brightness. Two mornings later, on the 17th, I finally had a clear sky, and I could detect the comet even in binoculars as a moderately condensed object of 8th magnitude. Telescopically it appeared quite "solid," although I could not detect the thin ion tail that appears on some images I've seen.
At this point, I would almost consider it anybody's guess as to what this comet might do as it approaches perihelion; in all the years I've been observing comets, and all the comets I've observed during those years, I don't think I've ever seen behavior quite like this. I still tend to think that some kind of disintegration scenario is the most likely, although the strength of the current upsurge in brightness and the comet's overall "solid" apperance tend to argue against this. If it brightens "normally" from this point onward, the comet might well reach naked-eye brightness -- although probably not conspicuouly so -- in early August before it disappears into the dawn sky. About all we can do right now is sit back and see that the comet tells us.
It occurs to me, incidentally, that if the only information I had to go on were my two observations thus far, I would almost certainly have erroneously concluded that the comet had brightened steadily and solidly between those two observations. It's good that we've got eyes around the world watching these things!
MOST RECENT OBSERVATION: 2018 July 17.44 UT, m1 = 8.2, 5' coma, DC = 5 (10x50 binoculars)
UPDATE (August 8, 2018): It is now clear that the dramatic brightening that this comet underwent in mid-July was its "last hurrah" as it proceeded through the process of disintegration. When I observed it again four mornings later it had faded by over a magnitude and a half, and it was distinctly less condensed. While that would end up being my final observation of Comet PANSTARRS, reports and images until the beginning of August (at which point its elongation became too small) from my colleagues around the world documented that it continued fading and diffusing out, until there wasn't much left but a cloud of debris. There will probably be little, if anything, left of it by the time it passes through perihelion.
Once again, the northern hemisphere misses out on a potential bright comet . . .
In some of the "Countdown" and the "Counting Comets" entries I discussed the comets that have been discovered by various artificial spacecraft missions. One of these is NASA's Wide-field Infrared Survey Explorer (WISE) mission, a next-generation successor to the highly successful InfraRed Astronomical Satellite (IRAS) mission that surveyed the entire sky in infrared wavelengths for ten months in 1983 and which, among many, many other discoveries, found six comets (seven, if one includes the Geminid parent "comet" (3200) Phaethon).
WISE was launched on December 14, 2009, and thereafter spent the next ten months surveying the entire sky at four different infrared wavelengths, with much higher resolution and sensitivity than IRAS was able to achieve. During this time frame WISE discovered 17 comets, and I had hoped to add at least one WISE-discovered comet to my tally; unfortunately, however, all of these discoveries were very faint objects (in general, 19th or 20th magnitude or fainter), and I only attempted three of them, all unsuccessfully. My one semi-success was Comet 48P/Johnson (no. 491), which WISE recovered more than a year in advance of perihelion; curiously, that comet is currently visible in our skies on its subsequent return (no. 646).
Although WISE's coolant had ran out in October 2010, it remained a healthy spacecraft, with two of its four infrared detectors (at the shorter wavelengths) still active. After a period of hibernation, under the mission name of "NEOWISE" ("Near-Earth Object Wide-field Infrared Survey Explorer") WISE was re-booted with the primary mission of searching for Earth-threatening objects in Earth's vicinity. Since then it has discovered an additional 12 comets as of this writing, and I have fared somewhat better in observing these objects. My first Comet NEOWISE was a faint periodic object, P/2014 L2 (no. 547), and including the current comet my total now stands at 6. Although most of the NEOWISE comets I've seen have been rather faint, the previous one, C/2016 U1 (no. 608), had a small perihelion distance (0.32 AU) and briefly became visible with binoculars in the dawn sky as it approached perihelion in early 2017.
The ATLAS program in Hawaii first detected this comet on June 29, but when it was reported to the Minor Planet Center it was not described as having exhibited any cometary activity. When NEOWISE first detected the comet on July 2 it was clearly cometary -- hence the name -- and apparently as bright as 16th magnitude or brighter. Indeed, when I first saw it listed on the MPC's Probable Comet Confirmation Page on the 5th I had thoughts of making a visual attempt, however these stopped when I saw that the comet was just a few degrees from the position of the third-quarter moon that coming night, which made the thought of any worthwhile attempts hopeless. I did nevertheless succcessfully take an image with the Las Cumbres Observatory's facility at Teide Observatory in the Canary Islands, despite the bright moonlight.
The comet's discovery was formally announced the next day, but due to an unusually strong level of monsoon activity here in New Mexico we had rain and clouds for a solid week and a half, and I was unable to make any visual attempts during that time (despite the reports from various observers around the world which indicated it was moderately bright and easy to see). Finally, on the morning of July 17 I had relatively clear skies, and successfully observed the comet as a large, diffuse object of 10th magnitude.
Comet NEOWISE is traveling in a distinctly retrograde orbit (inclination 159 degrees, i.e., 21 degrees with respect to the ecliptic, but retrograde); essentially, it and Earth are "passing by" each other as they head off in opposite directions. It was closest to Earth (0.31 AU) and at opposition on July 27 (just a few days before perihelion passage), at which time it was traveling westward at seven degrees per day. Throughout this time it maintained a brightness between 9th and 10th magnitude, and meanwhile it was recorded in a series of test images obtained by NASA's Transiting Exoplanet Survey Satellite (TESS) mission on July 25.
Due to the summer monsoon and to personal matters that I will discuss in a future entry, I missed most of this comet's apparition, and it wasn't until early August that I obtained my second observation. At this writing a few days later it remains a large and diffuse object of 10th magnitude, and is accessible in the evening sky as it travels through the northern regions of the "head" of the constellation Scorpius. It is traveling towards the west-northwest and crosses into Libra within a couple of days, presently at a still moderately rapid rate of almost two degrees per day but decreasing to 15 arcminutes per day by the end of August, at which time it will be located a little over one degree southwest of the star Beta Librae. Although currently still around 10th magnitude, since it is rapidly receding from both the sun and the earth it should soon begin fading fairly rapidly, and I expect it will likely fade from view within the next few weeks.
INITIAL OBSERVATION: 2018 July 17.41 UT, m1 = 10.3, 4.5' coma, DC = 2-3 (41 cm reflector, 70x)
In January 1867 a 17-year-old recently-hired assistant at the Marseilles Observatory in France, Jerome Coggia, detected an unknown nebulous object, but was unable to follow up on it due to weather. A few nights later the Observatory's Director, Edouard Stephan (best known for his discovery of the galaxy group known as "Stephan's Quintet"), successfully confirmed the object as being a new comet and, probably due to Coggia's junior status at the Observatory, rather unfairly took credit for its discovery. Coggia would eventually go on to discover six additional comets (for which he did receive due credit), one of these being the object now known as Comet 27P/Crommelin, and another being a bright and conspicuous naked-eye object -- what could rightfully be considered a "Great Comet" -- in 1874.
The astronomers in 1867 followed the comet for the next 2 1/2 months, and were able to determine an approximate orbital period of 40 years. It was expected to return in the early 20th Century, and in fact it did pass through perihelion in 1904, however the viewing geometry was very unfavorable and it was not seen. It was eventually re-discovered on the subsequent return, in November 1942 by Liisi Oterma at the Turku Observatory in Finland (an astronomical institution that, fortunately, was able to remain quite active during World War II). The identity of Oterma's comet with the 1867 comet was established relatively quickly, and the orbital period was rather firmly established as being 38 years.
The comet next returned in 1980, under geometrical circumstances almost identical to those in 1942. I followed it for 5 1/2 months during that return (no. 38), and it reached a peak brightness near magnitude 8 1/2 (and being faintly detectable with binoculars) when near perihelion in early December.
And now, after another 38 years, P/Stephan-Oterma returns again. It was recovered as long ago as June 24, 2017 by the Pan-STARRS survey in Hawaii, as a very faint object of 21st magnitude. After being in conjunction with the sun earlier this year it began to emerge into the morning sky about three months ago, and when I made my first attempt for it on the morning of August 14 I successfully detected it as a small and somewhat condensed object slightly brighter than 14th magnitude. With this observation 38P/Stephan-Oterma becomes the longest-period comet that I've observed on two returns, breaking the previous record of 27.9 years held by Comet 27P/Crommelin that has stood since mid-2011 (no. 489).
The viewing geometry this time around is not quite as good as it was in 1980, but is still relatively favorable. The comet is presently a morning-sky object, being located in central Taurus some ten degrees south of the Hyades star cluster, and is traveling towards the east-northeast at just over half a degree per day. After crossing into northern Orion at the beginning of September and subsequently passing slightly north of the "head" of that constellation, the comet enters southern Gemini in mid-October and over the course of the next few weeks begins a turn more directly northward. Historically it tends to brighten (and fade) fairly rapidly, and thus it should be close to 11th magnitude during the latter part of September and 10th magnitude in October, and when at perihelion (when it will be located some three degrees southeast of the star Delta Geminorum) it should be near a peak brightness of 9th magnitude.
After perihelion the comet continues traveling towards the north-northeast, and crosses into Lynx shortly before mid-December. A few days after mid-month it is closest to Earth (0.77 AU), at which time it may still be as bright as 10th magnitude. It should start to fade somewhat rapidly after that point; meanwhile, it is at its stationary point in early January 2019, and at opposition shortly before the end of that month. The comet is at its farthest north point (declination +47.5 degrees) in early February and at its other stationary point a few days later; afterwards it begins a slow trek towards the south-southeast. It will likely fade beyond the range of visual detectability by sometime in March.
When I said good-bye to P/Stephan-Oterma on February 23, 1981 I was 22 years old; I was a young Officer in the U.S. Navy and had just recently reported for duty aboard ship, and was entering what I consider to be the darkest and unhappiest period of my life, a period that would shortly almost lead me to the point of suicide. A lot has happened since that farewell: I managed to get through that dark period, and left the Navy; I then went to work at the Jet Propulsion Laboratory and, among other things, in what I consider to be one of the highlights of my life helped ensure that the radio science experiment during the Voyager 2 encounter with Uranus in early 1986 was a success. I later returned to my home State of New Mexico and entered graduate school at New Mexico State University, successfully earning my Ph.D. in Astronomy with a thesis that, to my surprised delight, has apparently become one of the seminal investigations in the early study of exoplanets and that continues to be cited regularly in published papers. Meanwhile, I got married in 1985 and fathered two sons afterwards, both of whom are now grown and have turned into fine young men and who are pursuing their own lives and dreams. The marriage itself ended in divorce eight years ago, and since then I have had one serious relationship that ended unhappily but am now in another within which I am quite happy and content.
One of the most notable events during this entire period, certainly, was my discovery of Comet Hale-Bopp C/1995 O1 (no. 199) in 1995, which brought me worldwide fame and recognition and which has brought me a form of immortality that very few people in history have ever achieved. Despite some serious mistakes I made earlier in my life Hale-Bopp has allowed me to have a relatively decent "career" of sorts, including an eight-year stint teaching on-line University classes, a deep involvement in the developing commercial space industry (and in the development of Spaceport America), and -- most pleasing to me -- humanitarian efforts like the "science diplomacy" expeditons I led to Iran in 1999 and 2000 (that are described elswhere on this web site). I did much of this through the Earthrise Institute that I developed and that has, at least at times, produced a modicum of success.
And now, after all that and much more, at age 60 I say "Hello!" to P/Stephan-Oterma once again, and can show it what became of that young man who observed it all those years ago and who was just starting out on the "adult" phase of his life. I have had some semi-serious health issues in the recent past which among other things involved a week-long hospitalization last month, and I am presently on oxygen, although I am cautiously optimistic that that will be a temporary situation. As I indicated earlier I am now once again in a good romantic relationship, and I continue to retain good relationships with both of my sons. I continue to work with Earthrise and I have some efforts in the works -- some of which I discuss elsewhere on this web site -- although my recent health issues have thrown a bit of a wrench into these efforts. And, of course, just as I did back when I was 22, I continue to enjoy observing the night sky, including the visual comet observing, although as I have indicated elsewhere I am starting to feel the weight of advancing years and am contemplating "retiring" from -- or at least significantly slowing down -- this effort within the not-too-distant future.
I perhaps may have a bit more clarity on a couple of these issues by the time I am finished with P/Stephan-Oterma this time around, but once it's gone, I doubt rather strongly that I will be saying "Hello!" to it ever again. It next passes perihelion in August 2056 -- under only mediocre viewing geometry, although it should still reach 11th magnitude and be accessible without too much difficulty -- but the chances that I'll still be alive and still observing comets at the age of 98 are probably not very high. (Curiously, the near-Earth asteroid (433) Eros, which made its closest-observed approach to Earth in 1975 and my observations of which -- that I made into a Science Fair project that won several awards -- helped launch my astronomical career, will be making an equally close approach to Earth that same year.)
Meanwhile, P/Stephan-Oterma will almost certainly retain its status as the longest-period comet that I've observed on two separate returns indefinitely. The next opportunity to break its record does not come until 2042, when Comet Levy 1991q (no. 159) -- discovered in June of that year, and with an orbital period of 51 years -- makes its next return (under favorable viewing geometry, and passing 0.47 AU from Earth) but, as before, whether or not I'll still be alive and observing comets at the age of 84 is problematical. For whatever it's worth, I would be 103 when Comet 1P/Halley -- which I observed extensively during its return in 1986 (no. 85) -- makes its next return in 2061, but, we'll see . . .
INITIAL OBSERVATION: 2018 August 14.23 UT, m1 = 13.8, 0.4' coma, DC = 4 (41 cm reflector, 229x)
In this comet's "Countdown" entry for its 2009 return (no. 460) I discuss its discoveries and observational history, as well as my own personal history with it. (The one significant development since then is that the second discoverer, Tom Gehrels, passed away two years later, which I discuss in a subsequent "Countdown" entry.) As I recount in its entry, I followed the comet regularly for two months during its favorable 1981 return (no. 48), obtained just a couple of observations of it during the mediocre return in 1991 (no. 153), and -- just as I predicted in that entry -- managed just that one single observation of it in 2009.
On its present return the comet was recovered on May 25, 2018 by my friend Jim Scotti utilizing the 1.8-meter Spacewatch telescope in Arizona. As I also recount in its "Countdown" entry, this year's return is quite favorable, being similar to -- in fact, slightly better than -- that of 1981. It is at opposition at the end of September, and is nearest Earth (0.44 AU) on October 27, just a few days before perihelion passage. During this period of time it initially climbs northward through western Andromeda before beginning a sharp turn eastward in late October, at which time it will be located some four degrees south of the Andromeda Galaxy M31. It continues traveling eastward -- eventually turning slightly towards the east-southeast -- and crosses into northern Triangulum in late November, into northern Aries a month later, and then into Taurus in mid-January 2019, where it remains for the next 2 1/2 months. Based upon its brightness in 1981 -- when it exhibited some post-perihelion asymmetry in its brightness behavior -- the comet should reach a peak brightness between 10th and 11th magnitudes during November, and remain visually detectable until perhaps near the end of January.
Ordinarily, I would probably have begun looking for this comet during September. However, on August 14 an experienced visual comet observer in Poland, Piotr Guzik, reported that it was apparently in outburst, and this was quickly verified by various CCD images that were taken around that time. On the evening of the 14th, despite having to contend with less-than-ideal sky conditions I successfully observed the comet as a faint, diffuse, somewhat condensed object of 14th magnitude; my impression was that the outburst was already starting to subside.
Unfortunately, due primarily to our monsoon weather conditions here in New Mexico I did not have another opportunity to observe the comet before the full moon. My understanding from various reports I've read and images I've seen is that the outburst has essentially subsided and that the comet had faded, and is likely too faint for me to detect right now -- although I am hopeful that I will have an opportunity to look for it once the moon clears from the evening sky. While it is difficult to know exactly what to expect, my feeling is that as the comet approaches perihelion it will behave more-or-less as expected. But, we'll see . . .
In its "Countdown" entry for 2009 I noted that when I was following P/Swift-Gehrels in 1981 I was going through a very difficult time in my personal life. This was primarily due to the events that I discuss in the previous entry, although as I was concluding my last observtions of the comet I was beginning to see the proverbial "light at the end of the tunnel," and in fact just one week before my final observation I paid my first visit to the Jet Propulsion Laboratory, where I begin working two years later. In the "Countdown" entry I also expressed the hope that my life would be happier in 2018 than it was in 1981, and I would have to say that that is true; while I am presently dealing with the health issues that I discuss in the previous entry and while there are things in my life that I never accomplished (and some things I hopefully have yet to accomplish), I can at least look back over a life where I managed to do a few decent things. I like living where I do and for the most part I enjoy the work I am involved in, and that is not a bad way to be.
Once I say "good-bye" to P/Swift-Gehrels this time around, it is quite unlikely that I will see it again, as all future returns take place after the "retirement" timeline that I have discussed elsewhere. In any event, the next return, in 2028 (perihelion late March), is very unfavorable and there is no chance of observing it. The following return, in 2037 (perihelion mid-August), is a rather mediocre one, but any visual observers of that era should be able to detect it in the morning sky, albeit it will be somewhat dim. The return after that, in 2046 (perihelion mid-November), is another favorable one quite similar to the 1981 return and the one this year, and it should once again reach 10th or 11th magnitude. If I am still alive at the age of 88, regardless of whether or not I am still observing comets, I do hope that my life circumstances are such that I can be reasonably content like I am now -- and perhaps by then I will accomplished whatever else I have yet to accomplish in this life.
INITIAL OBSERVATION: 2018 August 15.23 UT, m1 = 14.0, 0.7' coma, DC = 3-4 (41 cm reflector, 229x)
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