CONTINUING WITH COMETS
TALLY ENTRIES 631-640
|631. COMET 24P/SCHAUMASSE Perihelion: 2017 November 16.93, q = 1.206 AU
A long-time acquaintance stops by for another visit. This comet was originally discovered as long ago as December 1911 by Alexandre Schaumasse, who observed from Nice Observatory in France. It was the first of three comets (the other two being long-period objects) that he discovered from Nice during the decade of the 1910s, a period of time during which he also served with the French Army during World War I and was severely injured. The comet was found to have an orbital period of close to 8 years (presently, 8.25 years) and while it has been recovered on most returns since its discovery, its perihelion distance of close to 1 AU means that on some returns it has remained on the far side of the sun for months at a time, and has gone unrecovered. On the other hand, on other returns it can become quite well placed for observation; in 1952 it passed 0.29 AU from Earth and at the same time apparently experienced an outburst of some kind, and for a while was as bright as 5th magnitude. The present return is the 11th (including its discovery return) at which it has been observed.
My personal history with Comet P/Schaumasse dates back to its 1984 return (no. 76), during the period of time when I was working with the Deep Space Network at the Jet Propulsion Laboratory in Pasadena, California, and was observing regularly with the experienced comet observer Charles Morris (who also worked at JPL). I followed the comet for 3 1/2 months during that return; when near perihelion in early December of that year it reached a peak brightness of magnitude 9 1/2 and I could faintly detect it with binoculars.
|Less than two days before I obtained my first observation of Comet P/Schaumasse, I received the tragic news that my lifelong best friend, Mark Bakke, had died of an accidental gunshot wound the previous month. Mark and I became best friends when we were in the Fourth Grade, during which time his family lived in New Mexico, and that friendship would continue when his family moved to North Dakota five years later, and on beyond that. In and around all the various things that best friends of that age do, I managed to get Mark interested in astronomy, and he soon surpassed me; he was the first of us to acquire a telescope, he was the one who discovered resources like the magazine Sky & Telescope, and so on. He was with me on that fateful night in early February 1970 when I saw my very first comet (Comet Tago-Sato-Kosaka 1969g) for the first time. He was also with me when I saw my first total solar eclipse, on February 26, 1979, which we observed from near Boissevain, Manitoba.
During the early 1980s when I was in the U.S. Navy and stationed in southern California, Mark was in the U.S. Air Force and stationed at Holloman Air Force Base in New Mexico, and I would get to see him when I returned to New Mexico on leave. While I could not have known it at the time, I saw Mark for the very last time in early January 1982, shortly before his enlistment in the Air Force was up and he returned to North Dakota; it is only fitting that on that final occasion we observed a comet together, Comet Bowell 1980b (no. 46).
|Mark Duane Bakke: March 20, 1957 -- September 24, 1984.|
|In my observing notes on the morning that I added Comet P/Schaumasse to my tally, I dedicated the observation to Mark and his memory, and in my mind I have always associated this comet with the memory of Mark. In addition to the sadness that came with losing the best friend I've ever had, I have long regretted that we never got to share in observing Comet Halley (no. 85), which came less than two years after his passing; also, we had long talked about discovering a comet -- possibly jointly -- and he never was able to share in the joy I experienced when I discovered my own comet the following decade. I am happy to say that I continue to remain in contact with members of his family.
I next observed P/Schaumasse on its return in 1993 (no. 174), during which it passed 0.55 AU from Earth and reached a peak brightness of 9th magnitude. That return came during the period of time during which it became necessary for me to leave my job at what is now the New Mexico Museum of Space History and during which I began to develop and build what is now the Earthrise Institute. P/Schaumasse next returned in early 2001 (no. 288), a somewhat mediocre return during which it got no brighter than 11th magnitude; nothing really dramatic happened in my life during that return, although I obtained my final observation just before departing for Zimbabwe for the June 21 total solar eclipse, and of course there were events that happened on a national and international scale later that year that dramatically affected the directions in which I eventually took Earthrise.
The comet was badly placed for observation at its return in 2009, and it was not recovered. On its present return it was recovered on July 24, 2017 by Jean-Gabriel Bosch and Alain Maury from the Observatoire de la Cote d'Azur's San Pedro facility in Chile's Atacama Desert, as a rather faint object of 19th magnitude. After one unsuccessful attempt in early October I successfully picked it up during my first attempt of the current dark run, on the morning of October 21; it appeared as a vague, diffuse object of 13th magnitude.
The current return is slightly inferior in quality to that of 1984, and similar to that of 2011 (with the exception that that was an evening-sky return). The comet remains in the morning sky throughout this return, and in fact remains near a constant elongation between 55 and 60 degrees for the next two months before this gradually increases. It is presently located in central Leo approximately eight degrees east of the bright star Regulus (and about 14 degrees east of the previous comet which, curiously, passes through perihelion only 19 hours before this one does) and is traveling towards the east-southeast at one degree per day. It crosses into northwestern Virgo in early November and spends the rest of 2017 traveling through that constellation. Just after perihelion passage it spends the next few days traveling through the southern section of the Virgo galaxy cluster, and it is nearest Earth (1.46 AU) on November 21. In early January 2018 Comet P/Schaumasse crosses into western Libra and spends the next month traveling across that constellation before crossing into northern Scorpius in early February and then into Ophiuchus shortly after the middle of that month, where it remains for the next 3 1/2 months.
Based upon the brightnesses I have observed during previous returns, I expect P/Schaumasse to reach a peak brightness between 10th and 11th magnitude during the second half of November, perhaps extending into early December. After that it should begin fading and diffusing out, and I will probably lose it in late January or early February.
Unlike what happened during some of the earlier returns of this comet, I don't seem to have to much in the way of dramatic events in my life happening at this time -- at least, not yet, anyway -- although as I continue the healing process that I discussed in my July 6 personal statement I am starting to see some potential future activities for Earthrise beginning to coalesce in my mind, and I may have something to write about in that regard before too much longer; stay tuned! Meanwhile, some unfortunate life circumstances have forced my younger son Tyler to relocate from Oregon back to New Mexico for at least the near-term foreseeable future; he arrived back here just a week ago, and most unfortunately experienced a rather severe car accident while en route (although, fortunately, he walked away from it with only minor injuries).
P/Schaumasse's next return, in 2026 (perihelion early January) is a distinctly favorable one, similar to that in 1993, with a minimum separation from Earth of 0.59 AU. This is somewhat after the "retirement" timetable I describe in my accompanying statement to "Continuing with Comets," although how closely I will actually stick to that timetable, and, indeed, what I might actually mean by "retirement," are things that remain to be seen. It occurs to me, though, that, given the association I have in my mind between Mark and this comet, and given that Mark was with me at the very beginning of my comet-observing "career," perhaps it might be appropriate to close out that "career" with this comet. Time will tell . . .
INITIAL OBSERVATION: 2017 October 21.46 UT, m1 = 12.8, 1.6' coma, DC = 1 (41 cm reflector, 70x)
During the time that I have been preparing this entry and the above entry, one of the most exciting discoveries in the entire history of solar system astronomy has been unfolding. On October 18 the Pan-STARRS program in Hawaii discovered a fast-moving object of about 20th magnitude, and over the course of the next couple of days additional observations indicated that it was traveling in an extremely elongated orbit and had passed perihelion at a very small perihelion distance (initially reported as about 0.15 AU, now more firmly established as 0.25 AU) over a month earlier; it was then placed on the Minor Planet Center's Possible Comet Confirmation Page. When I saw the object's listing on the PCCP on the 21st it seemed very strange that a comet as apparently instrinsically faint as this one seemed to be could have survived perihelion passage at such a small distance from the sun, and I wondered if perhaps there might be a dim outer coma attached to it that would make it brighter intrinsically and would be detectable visually; this occurrence is rare, but I have noticed it in a handful of previous comets. I made an attempt for it that evening, but didn't see anything.
On the 24th the Minor Planet Center formally announced the Pan-STARRS discovery as a comet under the designation C/2017 U1. Attention was called to the fact that all orbital solutions indicated a strongly hyperbolic orbit with an eccentricity near 1.2 which, if confirmed, can only mean one thing: this object came from interstellar space, perhaps having been ejected from another planetary system hundreds of millions of years ago, or longer. The fact that it arrived in the inner solar system from the general direction of the solar apex only strengthens this conclusion, as this is where we might expect interstellar comets to come from. Meanwhile, as of this writing, additional observations continue to support the hyperbolic orbit, however very deep imaging with very large telescopes has failed to reveal any signs of cometary activity, and thus it has been reassigned the designation A/2017 U1 (the "A" indicating the object is an asteroid that happened to be assigned a cometary designation). Regardless of what the object's true physical nature turns out to be, this clear detection of an apparent escapee from another planetary system is a most important discovery, and among other things tells us that the processes that go on in our solar system go on in other planetary systems as well. For what it's worth, the small perihelion distance, as well as the even closer approach to Earth's orbit -- indeed, it passed only 0.16 AU from Earth itself on October 14 -- brings to mind, and indeed is eerily reminiscent of, the "Rama" vehicle in the 1973 Arthur C. Clarke novel "Rendezvous with Rama," which passed through the inner solar system on a similarly hyperbolic orbit.
The newest addition to my comet tally is another Pan-STARRS discovery, but far more mundane than A/2017 U1. It was found almost two years ago, on November 2, 2015, at which time it was a very faint object near 20th magnitude located 7.4 AU and 7.1 AU from the sun and Earth, respectively. Because of its relatively large perihelion distance I never expected it to get bright enough to detect visually, however some of the recent reports I have read, and some of the recent CCD images I have seen (which show the presence of a distinct tail) suggested it might be worth attempting. After an unsuccessful attempt earlier in October I tried again on the evening of October 22 under very good sky conditions, and seemed to see an extremely faint "something" of magnitude 14 1/2 right near the limit of visibility of my telescope; I detected clear motion over an interval of two hours. On the following night the sky conditions seemed to be even better, and I once again saw the comet, which after an hour moved into a very good location with respect to the surrounding star field; despite its extreme faintness I could detect some structure within the moderately condensed coma, although I couldn't see any sign of the tail.
The comet is currently located in eastern Pisces approximately six degrees west of the star Eta Piscium, and -- traveling in a moderately inclined retrograde orbit (inclination 139 degrees) -- is moving towards the southwest at slightly less than half a degree per day. It remains within Pisces for the next 4 1/2 months, gradually moving over into the south-central part of that constellation. Although it is currently still over a month and a half away from perihelion passage, since it was already at opposition in mid-October and was closest to Earth (3.31 AU) on October 20, it is likely as bright now as it is going to get, and in fact should begin fading within the not-too-distant future. Since it is already near the extreme limit of my detectability, I will at most likely obtain only one or two more observations of it; indeed, it is distinctly possible that the two observations I have now are the only times I will see this comet.
CONFIRMING OBSERVATION: 2017 October 24.17 UT, m1 = 14.5, 0.6' coma, DC = 5-6 (41 cm reflector, 229x)
UPDATE (November 17, 2017): More or less as I expected, by early November Comet C/2015 V1 had faded beyond my range of visual detectability with the 41-cm telescope, and thus the two consecutive-night observations I obtained in October will remain my only sightings of this comet.
Meanwhile, the object designated A/2017 U1 that I discuss at the beginning of this entry continues to make news. Orbital calculations continue to indicate both a "before" and "after" eccentricity near 1.2, confirming that it entered the solar system from interstellar space, and will recede back into interstellar space (in the general direction of the "Great Square" of the constellation Pegasus). The Minor Planet Center has assigned it the permanent designatiuon of "1I" (the "I" indicating it is an interstellar object), and it has been given the name " 'Oumuamua" (from Hawaiian words meaning "a messenger from afar arriving first") by the Pan-STARRS discovery team.
One of the most productive of the space-based astronomy missions that have flown during the past few decades was the InfraRed Astronomical Satellite (IRAS) which, as its name indicates, surveyed the sky at medium- and far-infrared wavelenghts for ten months during 1983. Among its many discoveries were six comets, four of which I have observed: two of these are periodic comets that I have also seen on subsequent returns (126P/IRAS and 161P/Hartley-IRAS), and another was Comet IRAS-Araki-Alcock 1983d (no. 56), which passed just 0.031 AU from Earth in May of that year -- until a year and a half ago, the closest approach to Earth of any comet on my tally -- and which became as bright as 2nd magnitude in the process. Another one of its dramatic discoveries, which took place on October 11 of that year, was of a fast-moving object which Earth-based photographs revealed was a 16th-magnitude asteroid. Designated as 1983 TB, calculations soon revealed that it was traveling in a very elongated orbit (eccentricity 0.89) with an orbital period of 1.4 years and a perihelion distance of only 0.14 AU, the smallest of any asteroid that was known at the time.
This all occurred during a time of significant changes in my personal life. On Thursday, October 20, 1983, I received my discharge from the U.S. Navy, and a few days later I departed for my original home in New Mexico, in part to scout out potential employment and educational opportunities, and also to spend a last few days (and nights) at the house where I had been raised, as my father had just recently sold it and was in the process of moving. At the beginning of November, after one last observing session at my childhood home, I departed on the return trip to California, taking the northern route, i.e., through Flagstaff, Arizona, to scout out potential employment and educational opportunities in that area. One of the places I visited was the U.S. Naval Observatory's station in Flagstaff, and it was on the bulletin board there that I saw the just-issued IAU Circular 3881, wherein Fred Whipple pointed out that the orbit of 1983 TB coincided with that of the Geminid meteors.
The link between comets and meteor showers had long been established for over a century, but the Geminids, which are among the strongest of the "annual" meteor showers -- regularly producing rates as high as 60 to 100 meteors per hour when they peak in mid-December -- were an enigma, in that no parent comet had yet been identified. With Whipple's announcement, it appeared that, at long last, a parent for the Geminid meteors had finally been found. This immediately raised speculation that 1983 TB was not a "true" asteroid, but rather an extinct or dormant comet. A couple of astronomers made attempts to detect cometary emissions from 1983 TB as it headed away from the sun, but these were unsuccessful.
It so happened that on the inbound leg of its next return to perihelion, 1983 TB would pass 0.245 AU from Earth in mid-December 1984. By that time I was working for the Deep Space Network at the Jet Propulsion Laboratory in Pasadena, California, and was regularly observing from several of the nearby mountain sites, and since the ephemerides were suggesting that 1983 TB would be bright enough to detect visually, I decided to attempt it. I ended up observing it a handful of times over a two-week period in mid-December, during which time it reached a peak brightness of 13th magnitude and appeared entirely stellar through the 20-cm (8-inch) telescope I was using at the time. Even though it was still approaching perihelion, it began to fade dramatically as its phase angle increased -- exactly as an asteroid would be expected to do -- and by performing a light-curve analysis from my observations and those obtained by some of my colleagues I found that its brightness behavior was entirely consistent with that of a low- to moderate albedo asteroid.
Various other investigations carried out by astronomers all over the world also failed to reveal any signs of cometary activity in 1983 TB. In the February 1985 batch of the Minor Planet Circulars it was assigned the permanent asteroidal number (3200), and five months later it was given the name Phaethon from Greek mythology, "the son of Helios, who operated the solar chariot for a day, lost control of it and almost set fire to the earth."
While carrying out my observations and analysis of Phaethon during its 1984 passage by Earth, I found myself completely caught up in carrying out the research project, which included communication with various colleagues as well as literature searches, and I even conducted broadband filter observations of several asteroids of various spectral types as well as of several comets that were in the sky at the time (including the possible comet-to-asteroid "transition" Comet 49P/Arend-Rigaux (no. 79), which I discuss in its "Countdown" entry for its 2011 return (no. 496)). I ended up presenting my results at the National Astronomy Convention that was held in Tucson, Arizona in June 1985, and the paper I wrote was published in the Proceedings of that conference, my first published research paper. Ever since I had left the Navy I had been consumed by the question of "where do I go from here?" and the entire experience of observing and analyzing Phaethon re-lit a fire within me that had essentially lain dormant since I was in high school, and played a significant role in my decision to go to graduate school and seek my doctoral degree, a decision that would eventually lead to my return to New Mexico in 1986 and my enrollment in the Astronomy Department at New Mexico State University.
Phaethon, of course, has continued to make its regular orbits around the sun and make occasional somewhat close approaches to Earth ever since its 1984 passage. It passed 0.49 AU from Earth in November 1987 and should have reached 15th magnitude according to the brightness formula I derived from the 1984 observations, but during a couple of search attempts I failed to find it. While outbound from perihelion in 1993 it should have again reached 15th magnitude, and in late 1994 it should have reached 14th magnitude while passing 0.44 AU from Earth while inbound to perihelion, however both of these occurrences took place during the period of "displacement" during which I was living in El Paso, Texas, and thus having to transport the 41-cm telescope an hour into the surrounding desert -- something I was reluctant to do except on rare occasions. (I was also hindered by poor weather, and bad timing with regard to moon phases, during the times in question.) I would finally observe Phaethon again in December 2004, when during a distant approach (0.61 AU) to Earth while inbound to perihelion I was able to obtain a single observation of it as a stellar object of 15th magnitude.
Three years later, in December 2007, Phaethon passed just 0.121 AU from Earth, again while inbound to perihelion. I was able to obtain a handful of observations -- during which it again appeared completely stellar -- between mid-November and early December, and it reached a peak brightness of magnitude 12 1/2 before disappearing into the dawn sky. This was during the period during which I was conducting "Countdown," and while I did not include it as a tally entry, I did list it on the "Update" page during the period of time in question.
Phaethon's "status," as it were, took a dramatic turn in mid-June 2009 when it was near perihelion passage, when researchers noted that, in images taken with the Heliospheric Imager camera aboard the STEREO-A spacecraft, it was exhibiting a weak coma and tail activity, and furthermore had brightened a couple of magnitudes and was exhibiting a brightness behavior inconsistent with that of an asteroid. Analysis of the data indicated that Phaethon had indeed undergone a release of dust around the time of perihelion. Meanwhile, it exhibited a similar appearance and behavior in the STEREO-A images two returns later, when near perihelion in May 2012. At long last, Phaethon was finally exhibiting cometary activity, although as UCLA astronomer David Jewitt has pointed out, the repeated solar heating that Phaethon experiences during its regular close approaches to the sun would have completely depleted water and other volatile substances, and that the activity we are seeing is instead likely due to sun-baked fracturing of its crust, with dust then being swept away by solar radiation pressure. Jewitt and his colleagues have suggested that Phaethon could be considered a "rock comet," to distinguish it from the more conventional comets that are caused by sublimation of water ice and other volatiles. Jewitt notes, however, that the amount of dust released by Phaethon during its perihelion passages is at least an order of magnitude less than what is required to produce a meteor shower with the strength of the Geminids, and thus it is entirely possible that Phaethon was a more conventional comet in the past.
After all this, I was left with the question of whether or not a "rock comet" could be considered a "comet," at least for purposes of my tally. As I was working on my auto-biography, I decided I could justify the answer as being "yes," especially after considering Phaethon's activity near perihelion, its association with the Geminids (and thus the likelihood that it was indeed a more traditional "comet" in the past), and the fact that other "dusty" non-volatile objects had been assigned periodic comet designations by the IAU. At the end of 2014 I thus retroactively added to my tally the three returns during which I had observed Phaethon: the observations I obtained during its 1984 approach to Earth constituted tally entry no. 559, the single observation I obtained in 2004 was tally entry no. 560, and the observations I obtained in 2007 were tally entry no. 561. In all three cases, perihelion passage took place early the following year.
LEFT: Title and abstract of my paper concerning my observations of (3200) Phaethon in 1984. From Proceedings of the National Astronomy Convention, University of Arizona, 1985. RIGHT: A coma and dust tail on (3200) Phaethon, in a composite image obtained with the STEREO-A spacecraft on June 21, 2009. Image courtesy NASA/Jing Li and David Jewitt (UCLA).
When Phaethon passed perihelion in August 2016 it once again exhibited a diffuse appearance in STEREO images. On its outbound leg it passed 0.40 AU from Earth at the end of September, the best opportunity since its discovery for detecting possible post-perihelion cometary activity from the ground. I managed to observe it (no. 607) on a handful of occasions between late September and late October; on all occasions it appeared 15th magnitude and stellar, and no cometary activity was detected from anywhere.
The stage is now set for what should be one of the best opportunities we'll ever have for examining Phaethon during the foreseeable future. On December 16, 2017, Phaethon approaches to within 0.069 AU of Earth, the closest approach since its discovery, and the 7th closest approach to Earth on any comet on my tally. A wide variety of observations are being planned by astronomers worldwide, including radar bounce experiments from the Deep Space Network's large antenna in Goldstone, California.
After an unusual run of cloudy weather for this time of year, I successfully picked up Phaethon on my first attempt, on the evening of November 18; it appeared entirely stellar at 15th magnitude. At that time it was located in far eastern Auriga three degrees northeast of the star Theta Geminorum, and since it currently is coming almost directly towards Earth, it is traveling towards the northwest at barely over ten arcminutes per day. As it approaches Earth it rapidly brightens and its daily motion accelerates; by the beginning of December it will be located in central Auriga and traveling close to 45 arcminutes per day, and should be close to 13th magnitude. On December 10 it passes slightly over one degree south of the bright star Capella, at which time it will be close to 11th magnitude and traveling close to four degrees per day. One day later Phaethon crosses into Perseus and is at its highest northerly declination (+45.5 degrees) the day after that (by which time its motion will have increased to six degrees per day and its brightness to magnitude 10 1/2). On December 15 Phaethon crosses into Andromeda, and will be traveling rapidly towards the southwest at 11 degrees per day, and should be near its maximum brightness of 10th magnitude. At the time of its closest approach to Earth Phaethon will be in central Andromeda some five degrees east-southeast of the star Alpha Andromedae (Alpheratz -- the northeastern corner of the "Great Square" of Pegasus) and will be traveling at its maximum rate of 15 degrees per day; because of the rapidly increasing phase angle the brightness should have dropped to about magnitude 10 1/2.
The increasing phase angle continues to take a toll on Phaethon's brightness as it recedes from Earth. Shortly after its closest approach in enters Pegasus, and by the (western hemisphere's) evening of the 19th it will have entered Aquarius and will be crossing the iconic "water jar;" its motion will have dropped to 9 degrees per day, and the brightness to 12th magnitude. By December 22 Phaethon will have entered Capricornus and will have slowed down to just over 5 degrees per day, and will have faded to about 13th magnitude. Within another two or three days Phaethon will have faded beyond the range of visual detectability as it disappears into the dusk.
The close flyby of Earth this time around presents an excellent opportunity for gaining knowledge about this still-mysterious and enigmatic member of our solar system. An even better opportunity for scientific observations should come during the next decade, with the Japan Aerospace Exploration Agency's (JAXA's) Demonstration and Experiment of Space Technology for INterplanetary voYage Phaethon fLyby dUSt science (DESTINY+) mission. According to current plans DESTINY+ is slated for launch in 2022, and via the usage of ion engines will fly to within about 500 km (310 miles) of Phaethon within the subsequent four years.
While Phaethon has now been a part of my life for over four decades, the current flyby of Earth may very well be my "last hurrah" for this object which has had such a profound influence on my life (although I do hope to be around to see whatever results DESTINY+ might provide). It makes a somewhat distant approach to Earth (0.64 AU) in November 2020 but probably won't get any brighter than magnitude 15 1/2; meanwhile, on its outbound leg from perihelion it passes 0.37 AU from Earth in October 2026 and should reach magnitude 14 1/2. Just over a year later, in December 2027, under conditions very similar to those in 1984 it passes 0.27 AU from Earth and should reach 13th magnitude. Both of these latter two encounters take place after the "retirement" timeline that I have discussed elsewhere on these pages, although as I have also stated elsewhere I am uncertain as to how "solid" that "retirement" schedule might be, or even what I might mean by "retirement." In any event, I can say with some certainty that I will never have the opportunity to study Phaethon as well as I should be able to do so on the present return; not until December 2050 does it make a similar close approach (0.083 AU). Phaethon makes an extremely close approach to Earth -- 0.020 AU -- in December 2093, during which it should reach 9th magnitude or brighter, but I sincerely doubt I'll be around to witness that. But perhaps by then we'll have a pretty decent handle as to Phaethon's true physical nature.
INITIAL OBSERVATION: 2017 November 19.26 UT, m1 = 14.9, 0.0' coma, DC = 9 (41 cm reflector, 229x)
UPDATE (December 27, 2017): The above brightness scenario pretty accurately described Phaethon's behavior during this close approach. I measured a maximum brightness of magnitude 10.3 on the evening of December 12 before it began a slow, then more rapid, fading over the course of the subsequent week. It appeared completely stellar at all times -- no surprise -- and, as far as I know, every other observer also saw nothing but a stellar appearance.
While the above writeup states that radar bounce experiments were being planned from Goldstone, California, it turns out that the radar bounces were performed by the giant radio telescope in Arecibo, Puerto Rico -- the first such experiments since that instrument was damaged by the passage of Hurricane Maria back in September. The radar observations reveal that Phaethon is roughly spherical in shape and about 6 km (3.6 miles) in diameter, and appears to have a conspicuous dark feature -- possibly a crater -- near one of its rotational poles.
LEFT: Phaethon (bright "star" in center) as imaged by the Las Cumbres Observatory global network station at McDonald Observatory, Texas on December 13, 2017. RIGHT: Radar image of Phaethon obtained December 17, 2017 by the Arecibo radio telescope in Puerto Rico. Image courtesy Arecibo Observatory/NASA/NSF.
FINAL OBSERVATION: 2017 December 21.10 UT, m1 = 13.4, 0.0' coma, DC = 9 (41 cm reflector, 70x)
The second week of December 2017 has proven to be a rather interesting time for comet observing. The Gemind parent (3200) Phaethon (previous entry) is in the midst of its record-breaking close approach to Earth, being presently around 10th magnitude, and Comet PANSTARRS C/2016 R2 (no. 628) has been unexpectedly bright (close to 11th magnitude) and active despite its current heliocentric distance of 3.0 AU and is showing remarkable structure in its ion tail in some of the recent CCD images I've seen (some of which are strikingly reminiscent of those of the bizarre Comet Humason 1961e from over half a century ago). Meanwhile, in my latest statistical analysis I mentioned that the "Centaur" Comet 174P/Echeclus P/2000 EC98 (no. 384) might undergo additional outbursts in the future; it has just recently done so, and has recently been visible as a small condensed object slightly brighter than 14th magnitude -- the brightest at which it has ever been observed -- despite being over 2 1/2 years past perihelion passage and being located at a heliocentric distance of 7.3 AU.
And, I have just added another comet to my tally. This one comes courtesy of the Asteroid Terrestrial-impact Last Alert System (ATLAS) program, developed by the University of Hawaii and presently incorporating telescopes based at Haleakala and Mauna Loa (with more telescopes on a worldwide basis planned for the future). The first ATLAS telescope (Haleakala) went on-line in 2015, with the Mauna Loa telescope becoming operational earlier this year; since first going-on line ATLAS has discovered several dozen near-Earth asteroids and (as of present) eight comets.
The 7th ATLAS comet was discovered by one of the program's astronomers, Aren "Ari" Heinze, with the Mauna Loa telescope on October 2, 2017 (with pre-discovery images later being identified in images taken with the same telescope four nights earlier). The comet was a rather dim object of 18th magnitude located a little over 2.5 AU from the sun at that time, but has brightened steadily during the subsequent weeks as it has approached the earth and the sun. On November 22 I successfully imaged it with the 0.4-meter Sutherland, South Africa telescope of the Las Cumbres Observatory global network -- something I will have more to say about in a subsequent entry -- and its brightness on the image suggested it might be bright enough to attempt visually, but when I attempted to do so six nights later I was unable to see it. On my first attempt of the current dark run, late on the evening of December 12, I successfully observed the comet as a dim, diffuse, slightly condensed object slightly brighter than 14th magnitude. It appeared perhaps a couple of tenths of a magntiude brighter when I saw it again three nights later.
|Comet Heinze is traveling in a steeply-inclined retrograde orbit (inclination 96.9 degrees) and is currently located in western Hydra, in the eastern part of the "head" of that constellation, traveling slightly westward of due north at approximately 50 arcminutes per day. Its motion rapidly accelerates and gradually turns more westerly as it approaches Earth; it crosses into Cancer in a few days and passes two degrees west of the Praesepe star cluster (M44) on Christmas day (at which time its motion will have increased to 2 1/2 degrees per day). By New Year's Day 2018 it will have entered Lynx and will be traveling towards the northwest at six degrees per day; over the next two days it goes through opposition and enters northern circumpolar skies, and when it passes closest to Earth (0.22 AU) on January 4 it will be located in southern Camelopardalis at a declination of +63 degrees and will be traveling at 7 1/2 degrees per day.
As Comet Heinze pulls away from Earth its motion through the sky starts to slow down, although it continues northward until reaching a maximum northerly declination of +68.9 degrees on January 6, at which time it will be located in northeastern Cassiopeia. Over the next few days it travels southwestward across that constellation, passing two degrees northwest of Beta Cassiopeiae (the westernmost star of the "W") on January 10.
|Comet Heinze C/2017 T1 (center), imaged on November 22, 2017, with the 0.4-meter telescope at Sutherland, South Africa, of the Las Cumbres Observatory global network. The bright galaxies are NGC 2697 (center left) and NGC 2695 (below right).|
Over the next several days the comet crosses northern Andromeda and then into Lacerta, and begins to travel almost due southward as it descends toward the ecliptic plane on the far side of the sun. By late January it is in western Pegasus, again traveling at 50 arcminutes per day, and it will probably not remain in view for much longer, as it is in conjunction with the sun (32 degrees north of it) in mid-February. By the latter part of March it becomes accessible in the morning sky, being located then in central Aquarius and traveling towards the south-southeast at 40 arcminutes per day; it remains a somewhat difficult object for the northern hemisphere but increasingly becomes visible to observers in the southern hemisphere over the next few weeks as it enters southern circumpolar skies by the latter part of May.
Comet Heinze appears to be rather dim, instrinsically, as long-period comets go, and -- as is always the case anyway for long-period comets -- any brightness predictions must be regarded as uncertain. Based upon the initial brightness measurements I have made, and under the assumption that the comet brightens "normally," it may be as bright as 11th magnitude, possibly 10th, by late December, and may be up to a magnitude brighter when it is nearest Earth in early January. It may then fade by perhaps a magnitude or so by the time it disappears into evening twilight in early February. If it is still visible when it reappears in the morning sky during late March, it is likely to be rather faint -- no brighter than 12th or 13th magnitude -- and it will probably fade beyond the range of visual detectability before much longer.
INITIAL OBSERVATION: 2017 December 13.29 UT, m1 = 13.8, 0.7' coma, DC = 3-4 (41 cm reflector, 229x)
As my observing skills have increased over the many years that I have been observing comets, and as the comet discovery rate has increased as well (especially as a result of the comprehensive surveys that have been on-line for the past two decades), the average number of comets that I observe each year has steadily increased. For most of my first decade of comet observing I would usually only reach a maximum of about five comets each year. In 1983 I finally succeeded in reaching double digits (actually observing 11 comets that year), and I have always manage to observe at least 10 comets in every subsequent year. Due to an unusually large number of returning periodic comets I actually succeeded in observing 20 comets the following year (1984), and after achieving that number on an occasional basis for the next decade and a half I began doing so on a regular basis once the comprehensive surveys came on-line in the late 1990s. I hit 30 comets for the first time in 2002 (actually observing 34 comets that year), and ever since then I have managed to observe 30 or more comets during about half of the subsequent years. My current record for most comets in one year is 39, in 2015.
With just over a week to go, I finally managed to observe my 30th comet in 2017, but I had to work for it. The comet in question was discovered on September 30, 2017, by Greg Leonard during the course of the Catalina Sky Survey in Arizona, although since it was not readily apparent at discovery as being a comet, it was assigned the name "Catalina" once its cometary nature was established. Being a relatively dim object of 18th magnitude at discovery, and traveling in a moderately-inclined retrograde orbit (inclination 153 degrees), Comet Catalina spent most of the next two months traveling westward through northern circumpolar skies, being at opposition in early November and reaching a peak northerly declination of +65.6 degrees in the middle of that month, before beginning to descend southward in the northwestern evening sky. It brightened slowly during that time -- being closest to Earth (1.21 AU) in late November -- but according to most reports I read it was remaining too dim for worthwhile visual attempts. I made one attempt for it in early December -- the same night I added the previous comet to my tally -- but didn't see anything, and had planned to try for it again before the moon began washing out the evening sky. Before I made that second attempt I read a report and saw images that suggested the comet had recently brightened, and on the evening of December 23, while fighting moonlight and thin cirrus clouds, I saw a very faint (13th magnitude) diffuse object in the comet's expected location that moved as expected during the half-hour that I watched it. On the following night, with perhaps slightly better sky conditions (albeit still with some scattered thin cirrus clouds) but brighter moonlight, I again saw a very faint diffuse object in the right location and with the expected motion, verifying that I had indeed observed the comet.
Comet Catalina is currently located in northern Pegasus near the star Beta Pegasi (the northwestern star of the "Great Square") and is traveling slightly westward of due south at a little under one degree per day. With the ever-brightening moon in the evening sky I am very probably done with it for the current dark run, and will likely not see it again until sometime in early January, by which time it will be well "down" the westward side of the "Great Square" and slowing down as it recedes from Earth. On January 19 the comet passes four degrees west of Alpha Pegasi, or Markab (the southwestern star of the "Great Square") and it will have slowed down to 20 arcminutes per day. How bright Comet Catalina might be during this time is difficult to predict, although I suspect it may be slightly brighter than it is now (since it is still approaching perihelion). Meanwhile, by late January it will be getting quite low in the northwest after dusk, and with the brightening moon in the evening sky at that time I will probably lose the comet sometime during this period.
The comet is on the far side of the sun from Earth at the time of perihelion passage, and is in conjunction with the sun (10 degrees north of it) in early March. By the latter part of April it begins emerging into the morning sky, being located a few degrees east-southeast of the "water jar" in Aquarius, and continues its southward trek over the next several weeks. I suspect the comet will have faded beyond the range of visual detectability by that time, although we won't know that for sure until that time gets here; for what it's worth, observers in the southern hemisphere will have it more easily accessible than will those of us north of the Equator.
CONFIRMING OBSERVATION: 2017 December 25.18 UT, m1 = 13.4, 0.7' coma, DC = 1-2 (41 cm reflector, 229x)
UPDATE (January 10, 2018): Some images I've seen and reports I've read suggest that the late-December upsurge in brightness that this comet underwent and that led to my successful observations of it may have been due to an outburst, or -- perhaps even more probable -- the first act of disintegration. (This is rare, but not unheard of, for long-period comets approaching perihelion.) Indeed, some of the images I saw that were taken in very late December and just after the beginning of 2018 -- albeit in bright moonlight -- suggested that the disintegration process was continuing. Once the moon had cleared from the evening sky I made an attempt for Comet Catalina on the evening of January 4, and successfully detected it, however it appeared as only an extremely vague, diffuse 14th-magnitude patch of light that was little more than a "presence." An image I took via the Las Cumbres Observatory telescope network a few hours later showed the comet as only a dim, diffuse smudge. It thus appears that this comet may indeed be disintegrating, and I am very probably finished with it.
MOST RECENT OBSERVATION: 2018 January 5.12 UT, m1 = 13.8, 1.0' coma, DC = 0 (41 cm reflector, 229x)
The New Year of 2018 has now arrived at Planet Earth. While my own personal New Year's celebration was quite enjoyable -- for reasons which I may share at a later time -- the New Year itself has, thus far, been a rather difficult one for me emotionally, as several people, including those I consider personal friends as well as those whom I have admired, have just passed away. This started with former astronaut Bruce McCandless, who passed away on December 21, whom I got to know moderately well as he and his late wife Bernice were part of my second "science diplomacy" visit to Iran, in July 2000. Marie Bakke -- mother of my childhood best friend Mark, whom I discuss quite extensively in my entry for Comet 24P/Schaumasse (no. 631) -- passed away just before New Year's; in a somewhat ironic twist, I made what is probably my last observation of that comet on its current return, and quite possibly my last observation of it ever, just a couple of days before she died.
Just a few days ago I learned that my Hale-Bopp co-discoverer, Thomas Bopp, passed away at the age of 68. He and I had been in occasional contact over the years, and I had last seen him in June 2016 at the SpaceFest conference in Tucson, Arizona (with health issues apparently preventing him from attending the SpaceFest last year, which I did attend). At the same time, I learned that former astronaut John Young, who had walked on the moon as part of the Apollo 16 mission and who, among other flights, also commanded the first Space Shuttle mission, had just passed away. All of the astronauts of that early era were my heroes, and I had the privilege of meeting him once at a Space Frontier Foundation conference in Los Angeles several years ago. And, finally -- I hope! -- I've just learned that Ray Thomas, of the British rock band The Moody Blues -- one of my all-time favorite bands, dating back to my early high school days -- has just passed away. I am glad I was able to attend a couple of Moody Blues concerts (including one at The Greek Theatre in Los Angeles) when I was living in southern California during the early 1980s.
Provided that this rash of deaths can ebb for a while, this New Year of 2018 does show some promise of being an interesting and meaningful year for me. I continue to progress in my "re-engagement" of Earthrise, and I hope I have something to say about that in the not-too-distant future. As far as comets are concerned, 2018 looks to be a very good year: several bright and notable periodic comets are making favorable returns this year -- including one which is coming close to Earth and should reach naked-eye brightness -- and a long-period comet discovered in 2017 also shows some promise of reaching naked-eye visibility (albeit the show will likely be rather brief). On a personal level, if my father, Nile Hale, were still alive, he would be celebrating his 100th birthday in September; he was the person who helped get me interested in astronomy in the first place, way back when I was in Elementary School. And, in a couple of months I will "celebrate" the big 6-0 (ugh!).
As if to set the stage for all the comets that are coming this year, 2018 begins as a rather busy year for these objects. Comet Heinze C/2017 T1 (no. 634) is in the midst of its moderately close approach to Earth, although it has remained somewhat faint, not getting much above 11th magnitude. Comet PANSTARRS C/2016 R2 (no. 628), also currently near 11th magnitude, has been found to be unusually rich in ionized carbon monoxide, and has been exhibiting enormously dynamic activity in its ion tail. Amongst these and others, I have also added my first two tally additions of the New Year, both on the evening of January 5; this is the 33rd occasion during my years of comet observing wherein I have added two or more comets to my tally on the same night.
The first of the tally additions is an old friend, which was originally discovered in August 2001 by a Canadian amateur astronomer, Vance Petriew, and which I successfully confirmed (no. 294) the following morning both visually and with the CCD system which was operational at the time, becoming -- much to my satisfaction -- the first person in the world to obtain accurate astrometry on it and being so listed in the discovery announcement. It was found to have the relatively short orbital period of 5.5 years, and I had successfully observed it on both subsequent returns, in 2007 (no. 400) and in 2012 (no. 506); I discuss it somewhat extensively in its "Counting Comets" entry for the latter return. Earlier that month I had experienced the (first) breakup of my previous relationship, and was emotionally devastated in the aftermath; my observations of Comet Petriew, although they were few in number, helped in setting me on the long and difficult road to healing.
On its current return Comet Petriew was recovered on July 18, 2017 by Jean-Gabriel Bosch and Alain Maury from the Observatoire de la Cote d'Azur's San Pedro facility in Chile's Atacama Desert. It was reported as a very faint object of 20th or 21st magnitude, and it apparently remained quite faint for the next several months, as only a handful of observations were reported. I successfully imaged it (in bright moonlight) in early December with the Las Cumbres Observatory network, although it appeared as little more than an extremely faint and tiny smudge of light, and then made a couple of unsuccessful visual attempts later in December. When I made my first attempt of the current dark run I successfully observed it as a vague and diffuse object slightly brighter than 12th magnitude, located well within the zodiacal light.
The current return is similar to, albeit slightly better than, the return in 2007. The comet is currently located in central Aquarius, at an elongation of 41 degrees and about six degrees east of the star Xi Aquarii, and is traveling slightly northward of due east at just over one degree per day (passing just over 15 arcminutes north of the star Theta Aquarii on January 12). As it approaches the sun and Earth its apparent motion gradually accelerates and its elongation gradually increases; meanwhile, it crosses into western Pisces at the end of January and into western Cetus a week and a half later. The comet is nearest Earth (1.33 AU) just after mid-February, at which time its elongation will have increased to 47 degrees and it will be exhibiting its maximum apparent motion of 75 arcminutes per day; on the 17th it passes 50 arcminutes south of the Local Group galaxy IC 1613. Afterwards it briefly crosses the southeastern corner of Pisces before crossing back into Cetus near the beginning of March, where it remains for the next few weeks.
Based upon its behavior at previous returns, I expect Comet Petriew to brighten gradually over the coming weeks, to a peak brightness of about 11th magnitude, perhaps slightly brighter, in late January and early February. Afterwards it should begin fading, and I expect to lose it by sometime in early March.
With its present orbital period future returns of Comet Petriew will continue to alternate between morning sky and evening sky, with the morning sky returns becoming progressively less favorable and the evening sky returns becoming more so. I should still be able to observe it during its next return in 2023 (perihelion mid-July), but whether or not I'm still observing comets at the return after that (perihelion late December 2028, and during which it approaches to 0.87 AU of Earth) remains to be seen. A series of close approaches to Jupiter during the mid-21st Century will increase the comet's perihelion distance to slightly over 1.4 AU by the end of the Century, but of course I will be long gone by then.
INITIAL OBSERVATION: 2018 January 6.08 UT, m1 = 11.7, 1.7' coma, DC = 1 (41 cm reflector, 70x)
Throughout "Countdown" I made frequent reference to the Siding Spring Survey based in New South Wales which, as the only comprehensive survey program based in the southen hemisphere, contributed a non-trivial number of comets to my tally. With the demise of the Siding Spring Survey due to lack of funding in mid-2013, there has been a significant "hole" in the amount of sky that has been searched for comets and near-Earth asteroids. There have been a couple of efforts by amateur astronomers in the southern hemisphere to take up some of the slack; for example, my friend Terry Lovejoy in Queensland, who contributed two of my comets in "Countdown" (including no. 500) and an additional entry in "Counting Comets" (no. 532), has found two more since then, including C/2014 Q2 (no. 556) which became a naked-eye object of 4th magnitude in late 2014 and early 2015, and C/2017 E4 (no. 617) which briefly reached close to magnitude 6.5 last April.
At this time the most productive effort in the southern hemisphere is the Southern Observatory for Near Earth Asteroids Research (SONEAR) program, operated by a group of Brazilian amateur astronomers and based in Oliveira, Minas Gerais. Since becoming operational around the beginning of 2014 SONEAR has thus far discovered six comets and almost 30 near-Earth asteroids (as well as several main-belt asteroids). Half of SONEAR's comet discoveries have been made by Cristovao Jacques: his first one, C/2014 E2 (no. 540), reached 6th magnitude and briefly flirted with naked-eye visibility in mid-2014, and a little over a year later his second one, C/2015 F4 (no. 574), peaked at 11th magnitude.
Cristovao discovered his third comet on May 29, 2017; at that time it was a faint object of 18th magnitude, located in southern circumpolar skies at a declination of -57 degrees. It traveled southward from that point as it slowly brightened, eventually reaching a peak southerly declination of -81 degrees at the beginning of October before turning back northward. It was still at a declination of -68 degrees when I imaged it remotely on November 24 with the Las Cumbres Observatory network; its brightness on the image suggested it was approaching the point of visual detectability, and indeed I soon began to read of visual observations from the southern hemisphere. The comet finally became accessible from my latitude in late December, however by that time there was already significant moonlight in the evening sky, and that (as well as some cloudy weather) precluded any attempts. Finally, on the evening of January 5, 2018 -- not much more than half an hour after obtaining my first observation of the above comet -- I successfully observed Comet Jacques not too far above my southern horizon (at a declination of -41 degrees). It appeared relatively small and condensed, and was slightly brighter than 14th magnitude.
The comet has just recently passed through perihelion, and was also nearest Earth (1.82 AU) shortly after mid-December, and thus is likely
|Comet Jacques C/2017 K6 (above center) imaged with the Las Cumbres Observatory station at the South African Astronomical Observatory on November 24, 2017.|
already as bright as it is ever going to get. It is presently located in southwestern Fornax, some three degrees north of the star Phi Phoenicis -- and, from my latitude, already at its highest above the horizon by the time darkness falls -- and is traveling slightly eastward of due north at 45 arcminutes per day. It crosses into southeastern Cetus at the end of January and then into northwestern Eridanus in mid-February, where it remains for the next few weeks. By sometime around that time I suspect it will have faded beyond the range of visual detectability.
INITIAL OBSERVATION: 2018 January 6.10 UT, m1 = 13.8, 0.8' coma, DC = 4-5 (41 cm reflector, 229x)
A few entries back I commented on a "trio" of unrelated long-period comets, all discovered by Pan-STARRS in mid-2016, and all passing through perihelion in mid-2018 at heliocentric distances between 2.2 and 2.7 AU. I picked up the first two comets of this "trio" within two days of each other last September: C/2016 R2 (no. 628) is now well placed for observation in the evening sky, at 11th magnitude, and has been found to be a member of a rare chemical class of comets and has been exhibiting very dynamic evolution of features in its ion tail; meanwhile, C/2016 M1 (no. 629) remained faint at 14th magnitude up through early November, by which time it was becoming inaccessible low in the western sky. It was in conjunction with the sun (33 degrees north of it) in late December and is now beginning to emerge into the morning sky; I hope to pick it up again (at, presumably, a brighter magnitude) sometime within the next month.
With the addition of this comet to my tally, the "trio" is now complete. Chronologically, it is the middle comet of the "trio," both in terms of its discovery (which took place on July 14, 2016) and its perihelion passage. I began searching for it in June 2017 and made a handful of attempts up through mid-October; I had an extremely faint suspect on an occasion or two but nothing I could ever verify. After conjunction with the sun (63 degrees north of it) in early November it began to emerge into the morning sky by late that month, and I made a handful of additional attempts through mid-December; once again I had very faint suspects on a couple of occasions but could never verify these. Finally, on my first attempt of 2018, on the morning of January 15 (after the moon had cleared from the morning sky), I clearly saw the comet as a small, faint, moderately condensed object slightly brighter than 14th magnitude that exhibited clear motion over a period of an hour and a half.
The comet is presently located in eastern Draconis approximately two degrees west of the star Theta Draconis and, traveling in a steeply inclined retrograde orbit (inclination 106 degrees), is moving almost due northward at a little over 20 arcminutes per day. It soon enters northern circumpolar skies, crossing into southern Ursa Minor in early February and passing just five arcminutes west of the star Gamma Ursae Minoris ("Pherkad," the southern and dimmer of the two stars at the end of the Little Dipper's "bowl") on February 16 and then 45 arcminutes northeast of Beta Ursae Minoris ("Kochab," the brighter of the Little Dipper's "bowl" stars) six days later. The comet reaches its maximum northerly declination, +80.5 degrees, in mid-March, at which time it is also at opposition, and possibly a magnitude or so brighter than it is now. By early April it begins a strong southward plunge through Camelopardalis and Lynx, and may fade slightly by the time it disappears into the northwestern dusk in early June.
Comet PANSTARRS is in conjunction with the sun (10 degrees north of it) in late July -- shortly after perihelion passage -- and begins to emerge into the morning sky by mid-September, at which time it will be located in eastern Cancer some five degrees southeast of the Praesepe (or "Beehive") star cluster M44. For the most part it continues its general southward plunge, crossing into western Hydra -- just east of the "head" of that constellation -- in early October, before making a westerly turn and crossing into Puppis in early December. The comet is actually closest to Earth (2.37 AU) on December 24 shortly before it crosses into northeastern Canis Major just before the end of the month. It is at opposition during the first week of January 2019, by which time it is traveling just south of due westward, and it passes 20 arcminutes south of the center of the star cluster M41 on January 16. Up until about this time the comet may have maintained something close to the brightness it exhibited throughout most of 2018, however once it passes through this opposition and thus is pulling away from both the sun and the earth, I suspect it will begin to fade rapidly, and I will probably lose it within another month or so.
As I was preparing this entry, Clarice Stone, mother of my friend and companion Vickie Moseley, passed away on January 16 at the age of 88, after a fairly long illness. Coincidentally, that same day is my older son Zachary's birthday; he has just turned 31. Time does not stop as the circle of life continues on: the number of years that have elapsed since Zachary was born serves to remind us of the amount of time that we have already spent on this planet, and Clarice's death reminds us that our remaining time is finite, and that we need to do whatever we can to make our time here on Earth count.
INITIAL OBSERVATION: 2018 January 15.47 UT, m1 = 13.7, 0.5' coma, DC = 6 (41 cm reflector, 70x)
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