TALLY ENTRIES 641-650
|641. COMET LEMMON C/2018 EF9 Perihelion: 2018 May 23.12, 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 haved 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 Aurgia, 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)
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)
BACK to Comet Resource Center