TALLY ENTRIES 521-530
|521. COMET LINEAR C/2011 J2 Perihelion: 2013 December 25.30, q = 3.443 AU
This is one of the many comet discoveries of the LINEAR program in New Mexico (being discovered by LINEAR on May 4, 2011) and is another example of the nondescript long-period comets that often appear in my tally. I observed it for the first time on the evening of February 11, 2013, when it appeared as a tiny, condensed, and very faint object almost as faint as magnitude 14 1/2. It went through opposition at the beginning of March, and as I followed it for the next few months it seemed to brighten perhaps a couple of tenths of a magnitude, although it had faded back to the brightness I originally observed when I obtained my final pre-conjunction sighting at the end of May.
After being in conjunction with the sun (39 degrees north of it) in mid-August 2013, Comet LINEAR emerged into the morning sky, and it had brightened to slightly fainter than magnitude 13 1/2 when I saw it again at the beginning of October. It is now entering northern circumpolar skies, and it passes a little over 5 1/2 degrees from the north celestial pole on December 13; around that time it may be perhaps a half-magnitude brighter than it is now, and it should thereafter remain visually accessible through the first few months of 2014 as it moves over into the evening sky, travels southward, and fades. It is in conjunction with the sun (50 degrees north of it) at the end of March and is best visible in the morning sky after that.
The days of comets being discovered by amateur astronomers visually sweeping the skies are, if not completely gone foreover, at least greatly diminished; the last such discovery (Comet Ikeya-Murakami P/2010 V1 (no. 481)) was made over 2 1/2 years ago. But amateur astronomers do continue to make comet discoveries from time to time, although nowadays this is normally accomplished via CCD searches or searches with digital SLR cameras. Such was the case with this comet, which was discovered by Japanese amateur astronomer Masayuki Iwamoto on CCD images taken March 10, 2013. This is his first, and thus far only, comet discovery.
After learning of the comet's discovery I first observed it on the morning of March 15, when it was fairly low above the eastern horizon in the morning sky (its elongation at the time being 43 degrees); it appeared as a diffuse and somewhat condensed object of magnitude 12 1/2. I followed it for the next two months, during which it continued to remain fairly low in my eastern morning sky; for the most part it maintained the same total brightness, although it seemed to grow a bit more condensed. When I saw the comet for the last time on the morning of May 13, however, it had faded a few tenths of a magnitude and appeared more diffuse, and I didn't look for it any more after that.
523. COMET McNAUGHT C/2012 K6 Perihelion: 2013 May 21.50, q = 3.353 AU
Another Siding Spring survey discovery by Rob McNaught, which he found on May 27, 2012; this is the 25th time that his name appears on my tally. It was in southern circumpolar skies, at a declination of -66 degrees, at the time of Rob's discovery, and it traveled southward from there, reaching declination -77 degrees in mid-July before turning back northward; it remained deep in southern skies for some time thereafter, however, only becoming accessible from my latitude during the spring months of 2013. When at opposition near the end of April it was still at a declination of -42 degrees, although it continued to travel northward after that.
I had no plans to look for this comet, however I noticed that some of the CCD measurements were bright enough to suggest that visual attempts might be worthwhile. After one unsuccessful attempt early in May, when I attempted it again on the early morning of May 16 I was able to detect the comet as a faint diffuse object slightly fainter than 14th magnitude. I obtained a handful of additional observations over the next three weeks, during which time it seemed to brighten by a few tenths of a magnitude, although when I saw it for the last time on the evening of June 8 it had started to fade again. Incidentally, I had a rather dramatic view of it on the evening of May 30 when it passed through the same telescopic field as the relatively bright galaxy NGC 5078 and its companion IC 879.
I wrote in one of the "Countdown" entries about the career of Eleanor Helin -- known affectionately as "Glo" to her friends and colleagues -- who founded the NEAT program during the mid-1990s. Prior to her work with NEAT, during the late 1980s and early 1990s she conducted a photographic survey program with the 46-cm (18 inch) Schmidt telescope at Palomar Observatory in California, similar to (and somewhat in competition with) the highly successful program conducted by Carolyn and Eugene Shoemaker with the same instrument. Among the program's discoveries was this object, which was found in October 1989; Glo's assistants were Brian Roman and Jeff Alu (both of whom I had the opportunity to meet while visiting Glo at JPL the following year). The comet was found to have passed perihelion almost two years earlier and to be traveling in a low-eccentricity (0.17) orbit with a perihelion distance of 3.71 AU and an orbital period of 9.5 years. It became clear that this would likely be an "annual" comet observable throughout its orbit, and after being followed through aphelion en route to its next perihelion passage in 1997 it received the designation 117P.
While inbound to the subsequent perihelion passage in late 2005, in March 2002 the comet passed 0.68 AU from Jupiter, which increased the orbital eccentricity to 0.25 and shortened the orbital period to 8.2 years (currently, 8.3 years) and the perihelion distance to the present value. I had no real plans to look for the comet in 2005, however after reading about some CCD measurements that suggested it might be worth attempting, I obtained a handful of observations of it around the time it went through opposition in May of that year (no. 371), and a few more observations around the subsequent opposition near the end of August 2006. On all occasions the comet appeared as a tiny and faint object near 14th magnitude.
During its current return Comet 117P went through opposition near the end of April 2013, and when I attempted it on the early morning of May 17 I was able to see it as a tiny and very faint object slightly fainter than 14th magnitude. I subsequently observed it on a few additional occasions up through early August, with its overall brightness and appearance remaining essentially unchanged, but after that it was too low in my southwestern evening sky for further observations and I am done with it for the current opposition.
After passing behind the sun in December, the comet begins to emerge into the morning sky by March or April 2014, and is at opposition near the beginning of August. It should be perhaps a half-magnitude or so brighter than it was during the 2013 opposition, and visually detectable for several months, although it will remain quite faint.
My second Pan-STARRS comet should, like my first one, become a naked-eye object, although I don't expect it to become anywhere near as bright or spectacular as the earlier comet. It was discovered by the Pan-STARRS program in Hawaii on May 19, 2012, at which time it was located 8.79 AU from the sun and was reported as being about 19th magnitude. It was at opposition near the beginning of June 2013, and after a couple of unsuccessful attempts during May I successfully observed it on the evening of June 3 as a tiny, condensed, and very faint object slightly fainter than 14th magnitude (and located 5.59 AU from the sun and still 14 1/2 months away from perihelion passage). I thereafter followed it through the beginning of October, with its brightness and overall appearance remaining basically unchanged; after that it sank too low in my western sky after dusk to be observed.
The comet is traveling in a moderately-inclined retrograde orbit (inclination 142 degrees), and was in conjunction with the sun (30 degrees north of it) shortly after mid-November. I successfully picked it up in the morning sky on December 13, by which time it had brightened to 13th magnitude, and it will be at opposition again in late April 2014, when it may be as bright as 8th or 9th magnitude. It may brighten to 7th magnitude, perhaps 6th, by the time it disappears into evening twilight during July, and will pass behind the sun in early August (around which time it should be easily detectable in the LASCO coronagraphs aboard SOHO). The comet begins to emerge into the morning sky again by about the beginning of September (more easily observable from the southern hemisphere), and for the next month or so may be near its peak brightness, between 5th and 6th magnitude.
Comet PANSTARRS begins traveling rapidly southward after that, and is nearest Earth (0.95 AU) at the very end of October, and is at opposition a few days later; one week after that, it is at its farthest south, declination -56 degrees. It should fade quite rapidly afterwards as it recedes from Earth and heads back northward; at the beginning of 2015 it will likely be between 9th and 10th magnitude, and as much as one to two magnitudes fainter by the time it disappears into evening twilight during February. It is conceivable that the comet might still be visually detectable during the middle months of 2015 as it approaches opposition in mid-September, but if so it will likely be very faint.
I discussed this comet's history, and my own personal history with it, in its "Countdown" entry for its 2008 return (no. 429). At the end of that entry I indicated that I would probably not be able to observe the comet again until its return in 2029, however it had recently occurred to me that it might potentially be observable at its 2013 return, although it would be faint and low in my western evening sky, and the summer monsoon conditions here in New Mexico would make attempts rather problematical. It was recovered on November 25, 2011 by the Pan-STARRS program in Hawaii.
My first attempt in late June (when there was quite a bit of smoke in my sky due to a massive forest fire in western New Mexico) was unsuccessful, however during a brief dry spell on the evenings of July 8 and 9 I was able to observe the comet as a faint, vague, and diffuse object near magnitude 13 1/2. Somewhat surprisingly, I could still very faintly detect it at 14th magnitude when I looked for it again in early August, but I have no expectations of any further attempts -- at least, not until 2029 (assuming I am still active then).
During the second week of July 2013 I noticed a rather unusual object listed on the Minor Planet Center's Near-Earth Object Confirmation Page; it didn't seem especially bright, however it was in an unusual location, only 30 degrees from the sun in the morning sky (and close to the bright star Capella). I would subsequently learn that this was a comet that had been discovered on CCD images taken July 8 by an amateur astronomer in Ukraine, Gennady Borisov, as part of a deliberate search effort for comets at small elongations. While it was still listed on the NEOCP I made an attempt for it in relatively poor sky conditions on the morning of July 11 but didn't see anything; it turns out that the initial NEOCP orbit was a bit off and thus I wasn't quite looking in the right place. A more refined orbit became available later that day, and on the following morning, and under better sky conditions, I successfully observed the comet as a vague and diffuse object of magnitude 13 1/2. The appearance was similar when I observed it again two mornings later.
I had no expectations of seeing Comet Borisov again, despite some spotty reports I read that suggest the comet had brightened to somewhere between 11th and 12th magnitude by early August (which wouldn't be surprising). The already-small elongation continued to shrink, with the comet's moving southward throughout that time, and when at perihelion its elongation was only 23 degrees. The elongation did not exceed 30 degrees again until mid-October, by which time the comet was too faint for visual observations.
Comet Borisov appears to be an intermediate-period object; according to the most recent orbit calculations at this writing, it has an orbital period somewhere in the vicinity of 330 years.
One of the last comets that Rob McNaught discovered during the course of his work with the Siding Spring survey in New South Wales before its unfortunate demise was this one that he found on May 8, 2013, one of two comets he discovered on that night. (He would go on to make one additional comet discovery, C/2013 O3 on July 24, before the survey's termination.) It has since been found to be periodic, with an orbital period of 15.6 years, and apparently it has been within a remarkably stable orbit for several centuries, making only a handful of distant approaches to Saturn during that time. Indeed, it is apparently in a 3:4 resonance with Jupiter, i.e., it makes three orbits around the sun for every four orbits that Jupiter makes, thus keeping away from any close approaches to that planet.
I had no plans to look for this comet, however I read a couple of reports that suggested it might be worth attempting, and since the evening of August 8 was very clear and relatively dry -- a brief break from the intense monsoon activity that we in New Mexico experienced this summer -- I decided to give it a try. I was somewhat surprised to see a very faint, small, and relatively condensed object of magnitude 14 1/2, and it exhibited the expected motion over the course of the next hour and a half. Since the comet was at opposition on August 11, nearest Earth (1.16 AU) four days later, and at perihelion eight days after that, and thus theoretically was as bright as it was going to get, I had no expectations of seeing it again. However, when I attempted it again on the evening of the 26th I could still detect it as an extremely faint object right near the limit of visibility. I plan no further attempts.
Without a doubt this has been one of the most eagerly anticipated comets in many years. It was discovered on September 21, 2012 by Vitali Nevski of Belarus (one of the "Countdown" mentors) and Artyom Novichonok of Russia during the course of a survey program conducted by the International Scientific Optical Network, an international collaboration of telescopes run by the Keldysh Institute of Applied Mathematics in Moscow; the specific telescope used for the discovery is located in Kislovodsk, Russia. The comet was about 18th magnitude at discovery, although it was not immediately apparent that it was cometary (hence the name), and meanwhile prediscovery images to as far back as September 2011 have been identified in data taken with the Pan-STARRS program in Hawaii and (in late December 2011) with the Mt. Lemmon survey in Arizona.
Comet ISON's extremely small perihelion distance -- with the exception of the Kreutz sungrazers, one of the smallest ever recorded for a ground-observed comet -- drew immediate attention, and fueled much speculation that this could potentially become a "Great Comet." The more optimistic initial projections suggested that it might become bright enough for visibility during daylight around the time of perihelion, and be a bright and conspicuous naked-eye object both before and after that. The post-perihelion conditions were to be especially favorable for the northern hemisphere, with a potentially very long tail, favorable geometry for brightness enhancement due to forward scattering of sunlight, a closest approach to Earth of 0.43 AU on December 26, and a passage to within three degrees of the north celestial pole on January 7, 2014. These "Great Comet" speculations were tempered, however, with the realization that Comet ISON was apparently a first-time visitor from the Oort Cloud; such objects often tend to under-perform compared to original expectations, and indeed the comet's brightness essentially remained "flat" throughout most of the first several months of 2013. Furthermore, it did not seem to be an especially bright comet intrinsically, and thus there was a considerable possibility that it could disintegrate as it approached or passed through perihelion, in a manner similar to that exhibited by Comet Elenin C/2010 X1 (no. 487).
I visually attempted Comet ISON on numerous occasions between early January and early June, but never saw anything convincing. It then disappeared into sunlight, being in conjunction with the sun in mid-July. The first post-conjunction CCD images were obtained shortly before mid-August (when the comet's elongation was just under 20 degrees); these showed that there had been some brightening during the interim, although not very much. I was able to make my first post-conjunction visual attempt on the morning of September 1, when the elongation had increased to 32 degrees; low in the pre-dawn sky I was able to see the comet as a small and somewhat condensed object of 13th magnitude.
Initially Comet ISON brightened somewhat steadily, being near magnitude 11 1/2 in early October; at the beginning of that month it passed only 0.07 AU from Mars, and images were successfully obtained on September 29 by the Mars Reconnaissance Orbiter -- the first time that images of a comet have been taken from another planet. After that, however, its rate of brightening slowed dramatically, and even in early November it wasn't much brighter than 9th magnitude, although by then time it had developed a tail over 20 arcminutes long that was visually quite impressive when viewed telescopically.
Just before mid-month, meanwhile, the comet began to undergo some dramatic outbursts, and on the 15th I saw it near 5th magnitude, with a tail over 1 1/2 degrees long in binoculars. The comet faded slightly after that, but shortly thereafter began to brighten again as it made its final approach to perihelion. I obtained by final pre-perihelion sighting on the morning of the 21st, at which time its elongation had shrunk to slightly under 24 degrees; it appeared as a 4th magnitude star with a filmy 1 1/2 degree-tail in binoculars, although due to the low altitude and brightening sky I couldn't convince myself I was seeing it with my naked eye. Poor weather prevented additional observations on subsequent mornings.
On November 28, the date of perihelion, Comet ISON was a prominent object in the LASCO coronagraphs aboard SOHO. While initially it appeared to brighten to as far as magnitude -2, it thereafter began fading, and was no brighter than magnitude 0 when the C3 image at the right was taken. As it continued to approach the sun, disappearing behing the central occulting disk in the C3 coronagraph, and then in the inner, C2 coronagraph, Comet ISON clearly began to disintegrate. Perhaps a little surprisingly, it did emerge from behind the respective occulting disks, and although it initially appeared somewhat bright, it soon became obvious that what was being displayed was nothing more than a cloud of debris, and that the comet itself had completely disintegrated as it passed through perihelion.
For the next couple of days this debris cloud slowly traversed the C3 field of view, and clearly faded as it dispersed. (The lower C3 image, taken slightly over two days after perihelion passage, was one of the last ones before the comet exited C3.)
There was significant hope that this debris cloud might be detectable, via imaging and well as visually, when it had traveled sufficiently far enough away from the sun. By the second week of December various attempts by imagers around the world had failed to record any convincing sign of the debris cloud, and there were no convincing visual reports either. I made a comprehensive search for any remnant with the 41-cm telescope on the 14th, and thought I might possibly be seeing some "haziness," however I couldn't see anything of this the following morning, nor was there any confirmation from elsewhere. It appears, then, that Comet ISON is entirely gone, and that there is truly nothing left of it.
Despite its disintegration, and its failure to provide any decent show after perihelion, Comet ISON nevertheless goes down as one of the most scientifically studied comets in history. This is the first time that we have definitely seen a first-time visitor from the Oort Cloud pass so close to the sun. It furthermore has the unusual distinction of having been observed from three different planets in the solar system; not only was it imaged from Mars, but the MESSENGER spacecraft in orbit around Mercury imaged Comet ISON (as well as Comet 2P/Encke (no. 531)) when they passed by that planet.
In 1990 an amateur astronomer named Howard Brewington relocated from his native South Carolina to near my present residence in Cloudcroft, New Mexico. He had already discovered Comet Aarseth-Brewington 1989a1 (no. 133), which became dimly visible to the naked eye late the previous year, but he wanted to take advantage of the clearer New Mexico skies to hunt for additional comets. During the subsequent years he and I became friends, and he indeed managed to discover four additional comets up through mid-1996. He no longer hunts comets, but is still involved in astronomy as he is presently employed with the Sloan Digital Sky Survey.
Howard discovered his fourth comet (no. 171) in late August 1992, an 11th-magnitude object in the morning sky. It was found to have passed perihelion 2 1/2 months earlier, and also was found to be periodic, with a current orbital period of 10.8 years. It next returned in early 2003, under somewhat unfavorable conditions, but nevertheless reached 12th magnitude (no. 325). On its current return it was recovered on August 2, 2013, by Filip Fratev at the Zvezdno Obshtestvo Observatory in Plana, Bulgaria.
I made my first attempt of the current return on the evening of September 4, and successfully picked it up as a faint 14th-magnitude object. By the latter part of October it had brightened to about magnitude 11 1/2, and was exhibiting a rather vague and diffuse coma. Overall, this return is moderately favorable; the comet went through opposition at the end of August, and it remains well placed for observation in the evening sky for the next several months. It should reach a peak brightness near 10th magnitude, possibly 9th, around the time of perihelion, and remain visually accessible through the first one to two months of 2014.
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