TALLY ENTRIES 671-680
|671. COMET ATLAS C/2019 Y1 Perihelion: 2020 March 15.58, q = 0.837 AU
A new year . . . and a new decade. After quite a few upheaveals in my life, and a lot of "ups" and "downs" -- many of which I've described in previous entries -- during the just-completed decade of the 2010s, things seem to have settled down into a rather quiet normality for me as the 2020s begin, and overall I am reasonably content. Among other things, the "Ice and Stone 2020" educational program that I spent a good part of last year developing is underway, and while I have recently found it necessary to conclude the weekly "In Our Skies" newspaper column that I have written for the past 25 years, there are some other potential opportunities that I may be exploring within the not-too-distant future.
On the other hand, at my current age and especially within the context of the health issues I have encountered over the past couple of years, I begin the 2020s with the very real possibility that I will not be able to complete this decade at the activity level, both astronomical and otherwise, that I presently enjoy. It is entirely possible that at some point I may be forced to curtail my astronomical observing activities, and indeed I have discussed a potential "retirement" timeframe of mid-decade elsewhere on this web site. I have also had to come to terms with the potential possibility that I may not survive until the end of the decade. But, that part of my story, if that is indeed what it is, has not been written yet, and for the time being I am therefore continuing to take life as it comes one day at a time, and among many other things that means that I am continuing to observe comets.
|My first tally addition of the 2020s is a comet discovered on December 16, 2019 by the ATLAS program based in Hawaii. It was located at the southerly declination of -40 degrees, and perhaps 17th or 18th magnitude, at the time of discovery, but it seems to have brightened rapidly as it traveled northward, and images I took with the Las Cumbres Observatory telescopes as well as images taken by other observers elsewhere suggested it was developing an extensive outer coma. I made an initial visual attempt for it in late December and didn't see anything, but when I made my first attempt for it after the recent full moon, on the evening of January 13, I successfully detected it as a very vague and diffuse object of magnitude 12 1/2.
Comet ATLAS turns out to be a very interesting object, for it appears to be the fourth member of a "family" of comets that have been been appearing over the past three decades and that share almost identical orbits.The first member of this "family," and what was apparently the primary component, was Comet Liller 1988a (no. 116), which became a dim naked-eye object
|Comet ATLAS C/2009 Y1, imaged on January 15, 2020 -- slightly less than two days after I first observed it visually -- from the Las Cumbres Observatory facility at Teide Observatory in the Canary Islands.|
with a peak brightness between 5th and 6th magnitude during March and April 1988. (By an interesting coincidence, my first observation of Comet ATLAS came exactly 32 years, to the day, after my first observation of Comet Liller.) After 8 1/2 years, the second comet, Comet Tabur C/1996 Q1 (no. 219), appeared (with the orbital similarity to that of Comet Liller being first pointed out by German amateur astronomer Jost Jahn); although clearly fainter intrinsically than Comet Liller, it came closer to Earth, and also experienced a pre-perihelion outburst which briefly made it as bright as magnitude 4.5. This was apparently a disintegrative outburst, for afterwards Comet Tabur essentially dispersed away and only a vague cloud of debris was visible after perihelion. Then, after over 18 years a third member appeared, Comet SWAN C/2015 F3 (no. 569), with the orbital relationship being first pointed out by Worachate Boonplod in Thailand. Comet SWAN was significantly fainter than the previous two comets, never being brighter than about 10th magnitude, but in contrast to Comet Tabur it survived perihelion passage -- indeed, it was not even detected in images taken with the Solar Wind ANisotropies (SWAN) ultraviolet telescope aboard SOHO until just before perihelion -- although it did fade away fairly rapidly thereafter. (For what it's worth, I played a role in the confirmations of both Comet Tabur and Comet SWAN.) Detailed calculations carried out after the discovery of Comet SWAN indicate that the comets had previously returned around 945 B.C., with Comets Tabur and SWAN splitting from Comet Liller around that time.
The three previous members of the Comet Liller "family." Left: Wide-field view of Comet Liller 1988a (no. 116) on April 17, 1988 from Parkton, North Carolina. Courtesy Jim Skinner. Center: Comet Tabur C/1996 Q1 (no. 219) on October 12, 1996. The edge-on spiral galaxy M108 is to the comet's upper right, and the "Owl Nebula" M97 is in the lower right. Courtesy Gerald Rhemann and Franz Kersche in Austria. Right: Comet SWAN C/2015 F3 (no. 569) on March 26, 2015. Courtesy Francois Kugel in France.
And now, as was first pointed out by Dutch amateur astronomer Reinder Bouma, with Comet ATLAS we apparently have the fourth member of the Comet Liller "family." It is presently located in the evening sky, at an elongation of 50 degrees in eastern Aquarius near a declination of -15 degrees; it is traveling almost due northward at roughly 45 arcminutes per day, crossing into Pisces and then going north of the Celestial Equator in early February, then into eastern Pegasus two weeks later and into Andromeda in mid-March around the time of perihelion passage. It is in conjunction with the sun -- 37 degrees north of it -- a few days later, then crosses into western Cassiopeia just after the beginning of April; shortly thereafter it enters northern circumpolar skies while traversing the western portion of the "W" of that constellation. The comet reaches a peak northerly declination of +82.8 degrees on May 2, at which time it is also closest to Earth (1.09 AU) and thereafter heads southward, passing through the western part of the "bowl" of the Big Dipper during the fourth week of May and exiting northern circumpolar skies thereafter. It remains in the northern's hemisphere evening sky for several weeks afterward.
Ostensibly, more and more distant cometary fragments tend to have fainter and fainter intrinsic brightnesses, and thus we might expect that Comet ATLAS is even fainter, intrinsically, than Comet SWAN. My initial observation of Comet ATLAS suggests, however, that it has at least the same intrinsic brightness as Comet SWAN, and if that is indeed true then it might become as bright as 10th magnitude during March and April. On the other hand, the behavior of other fragmented comets, including Comet Tabur, suggests that any of several things could happen; it could undergo one or more significant outbursts and could briefly become quite bright, or it might just disintegrate and fade away as it approaches perihelion, or both, or something else entirely. We will just have to wait and see what the comet does as it makes its way through the inner solar system.
As for whether or not there are more members of this "family" that are still on the way in and that might appear during the years and decades to come, time will tell. However, unless any such comets happen to arrive within the relatively near future, I will probably have to leave any observations of these objects to some successor of mine.
A piece of trivia: when the IAU went to the new comet designation scheme at the beginning of 1995, it retroactively assigned new-style discovery designations to all pre-1995 comets in the manner that they would have been assigned had the scheme been in operation then. Within that context, with Comet ATLAS I have now observed the "9 Y1" comet for six consecutive decades, from the 1960s through the 2010s.
INITIAL OBSERVATION: 2020 January 14.08 UT, m1 = 12.4, 2.1' coma, DC = 1 (41 cm reflector, 70x)
|Fifty years ago, i.e., in mid-January 1970, at the age of 11 I acquired my first telescope, a 4.5-inch (11.4-cm) reflector sold by Sears. (I sold this telescope in the early 1980s and thus no longer have it, but, curiously, while rummaging around in some old papers a few years ago I discovered that I still have the operating instructions.) I immediately began using my new telescope, observing the moon, the various planets, and several of the brighter and more prominent deep-sky objects. Just a little over two weeks later I saw my first comet, Comet Tago-Sato-Kosaka 1969g -- an occasion that I will expand upon at the appropriate time in a future entry. Throughout all that has happened in my life during the intervening decades I have continued to observe the nighttime sky with whatever telescopes and other instruments I might have, and now, at the age of 61, I am still at it . . .
The first confirmed comet discovery of the 2020s was found on CCD images taken January 8, 2020, by Japanese amateur astronomer Masayuki Iwamoto, who has discovered three previous comets, all of which I have seen, including his most recent one (no. 658). The comet was very low in the eastern sky at dawn, and with only two positions -- barely over a minute apart -- available, and moreover with this being just before full moon, it remained unconfirmed for several days thereafter. Then, on January 13 Gennady Borisov in the Crimea -- another individual who has appeared on my tally several times, including with his most remarkable recent discovery (no. 670) -- accidentally re-discovered it. With these new observations now available other observers quickly began making astrometric observations of the comet, which in turn allowed a preliminary orbit to be calculated. Armed with this
|Instruction booklet for my first telescope.|
information, I successfully located it visually on the morning of January 14, although in the bright moonlight I couldn't tell much other than the fact that it was "there." In a somewhat darker sky four mornings later I could easily detect it as a vague and diffuse object of 12th magnitude. (Incidentally, with the addition of the previous comet on the evening of the 13th this marks the 36th occasion during which I have added two or more comets to my tally on the same night, and this is the fifth time I have done so by adding the first comet during the evening hours (i.e., before local midnight) and the second one during the morning hours, after local midnight.)
Comet Iwamoto is traveling in a relatively steeply-inclined retrograde orbit (inclination 121 degrees) and has approached the inner solar system from the south and from behind the sun, being in conjunction with the sun in mid-December and being at perihelion at the time of its discovery, at which time its elongation was still a relatively low 34 degrees. It is currently located in northern Ophiuchus -- the elongation having now increased to 45 degrees -- and is heading primarily northward, and over the next few weeks it travels through Hercules, Lyra -- passing half a degree west of the bright star Vega on February 7 -- and Draco; it enters northern circumpolar skies during the third week of February (being closest to Earth, 0.92 AU, on the 21st), is at opposition at the end of February, and is at its highest north declination, +78.2 degrees, during the first few days of March. Afterwards it travels southeastward through Cassiopeia, Camelopardalis, and Auriga, where it remains until near the end of May. The comet may brighten by perhaps a half-magnitude or so between now and early February but thereafter will probably fade beyond visual range by sometime in March.
Among the various events happening in the world right now (which I will mostly refrain from commenting on at this time), I have been saddened by the recent death (on January 7) of Neil Peart, drummer and lyricist for the Canadian rock band Rush, one of my favorite bands. I had the privilege of seeing Rush perform live in concert at Pan Am Center in Las Cruces, New Mexico in January 1992, just a few days after I had returned from a meeting of the American Astronomical Society in Atlanta, Georgia, during which I had presented the results of my Ph.D. dissertation and which had, to my delight, been rather warmly received. Several years ago the members of Rush gave me permission to use one of their songs for an audio/visual project I was developing to raise funds for Earthrise at the time, and in the meantime all three members (Peart, vocalist/bassist/keyboardist Geddy Lee, and lead guitarist Alex Lifeson) have had asteroids named for them. As I contemplate my own life, and my own mortality, the lyrics of their songs like "Dreamline" and "Time Stand Still" resonate ever more powerfully with me.
CONFIRMING OBSERVATION: 2020 January 18.52 UT, m1 = 11.8, 2.6' coma, DC = 2 (41 cm reflector, 70x)
Fifty years ago this month, on the evening of February 2, 1970, I observed my very first comet, Comet Tago-Sato-Kosaka 1969g; I included the at-the-telescope sketch I made of that comet that night in an earlier tally entry. I had hoped to mark the anniversary by observing at least one comet, but unfortunately the skies were cloudy that particular night; I did, however, manage to observe Comet PANSTARRS C/2017 T2 (no. 667) -- presently about 10th magnitude -- in a somewhat moon-brightened sky the following evening.
I'm under no illusions that I'll be keeping this up for another 50 years, but for at least the near-term foreseeable future I expect to continue observing whatever comets that come by and are bright enough to see. My first tally addition of my second half-century of comet observing is a rather interesting object that was discovered by the ATLAS program in Hawaii on December 28, 2019, at which time it was a very dim object of 19th magnitude. Ever since then I've been imaging it on a semi-regular basis with the Las Cumbres Observatory network and it has brightened fairly rapidly, and on an image I took on February 15 it seemed bright enough to be worth a visual attempt, however my attempt on the evening of the 16th was unsuccessful. Images that were taken by other observers over the next several nights, and even a couple of reports of visual observations, indicated that the comet was continuing to brighten, and after enduring several nights of cloudy and stormy weather I finally had another clear night on the evening of February 23 and clearly detected it as a diffuse and somewhat condensed object slightly fainter than 13th magnitude.
Two recent Las Cumbres Observatory images of Comet ATLAS C/2019 Y4, illustrating its rapid rise in brightness; both images are 5-minute exposures. LEFT: February 15, 2020, from Teide Observatory in the Canary Islands. RIGHT: February 27, 2020, from McDonald Observatory in Texas. Several background galaxies are visible in the image.
Comet ATLAS' small perihelion distance certainly brings attention. However, what really makes this comet interesting is the fact that its orbit is essentially identical to that of Comet 1844 III (new style designation C/1844 Y1), which is usually referred to as the Great Comet of 1844. That object was discovered from the southern hemisphere in December 1844 just after it had passed through perihelion, and which at its brightest was close to magnitude 0 and which exhibited a bright tail with a maximum length of about 10 degrees. The two comets are almost certainly fragments of an earlier comet which had split, presumably somewhere around the time of its previous return some 4000 to 4500 years ago.
At this time Comet ATLAS is entering northern circumpolar skies, being presently located in the southwestern "corner" of the "bowl" of the Big Dipper in Ursa Major, and traveling towards the northwest at close to 45 arcminutes per day. It is at opposition in early March and reaches a maximum northerly declination of +68.6 degrees at the end of that month, at which time it crosses into Camelopardalis. The comet continues traveling westward for some time thereafter, finally dropping south of declination +60 degrees at the beginning of May and entering Perseus a little less than two weeks later. From that point it begins a rapid southward plunge in the evening sky as it approaches perihelion, with the elongation dropping below 30 degrees on May 16 and with its being in conjunction with the sun (24 degrees north of it) on May 20. The final approach to perihelion will take place in the dawn sky, with the comet's passing 12 degrees due west of the sun around the time of perihelion passage. Thereafter it becomes accessible from the southern hemisphere in the morning sky, although by then it is on the far side of the sun from Earth and remains at a small elongation for some time, with this not exceeding 25 degrees until early July and not exceeding 30 degrees until three weeks later.
The potential for a decent display, and naked-eye visibility, from Comet ATLAS certainly exists, although the inherent uncertainty in making predictions of cometary brightnesses makes any projections quite problematical. In general, trailing fragments -- as Comet ATLAS apparently is -- tend to be smaller and thus fainter than leading fragments, so at face value there is no reason to think that it will become as bright as the 1844 comet. It is conceivable that Comet ATLAS itself could fragment, and thus undergo a surge in brightness similar to that of Comet West 1975n (no. 20) in 1976, but it is also conceivable that it could completely disintegrate and disperse, as did Comet ISON C/2012 S1 (no. 529) in 2013. One potential bit of good news is that, if Comet ATLAS should be a dust-rich comet and undergo a significant amount of dust release as it approaches perihelion, during that approach to perihelion it will be between Earth and the sun -- with a minimum distance from Earth of 0.78 AU taking place on May 23 -- and thus will be appearing at high phase angles (in excess of 130 degrees for a few days) and accordingly there could be some noticeable enhancement of its brightness due to forward scattering of sunlight.
All of this is just speculation, of course. My own "gut feeling" is that we will probably see a naked-eye comet, but not anything that could be considered a "Great Comet." But, I could be wrong . . . All we can really do is see what this comet reveals to us over the coming three to four months.
INITIAL OBSERVATION: 2020 February 24.22 UT, m1 = 13.3, 0.8' coma, DC = 3-4 (41 cm reflector, 70x)
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