COUNTING COMETS

TALLY ENTRIES 511-520

511. COMET 168P/HERGENROTHER          Perihelion: 2012 October 1.96, q = 1.415 AU

This comet was originally discovered in November 1998 by Carl Hergenrother during an early incarnation of the Catalina Sky Survey in Arizona. It was found to be periodic, with a current orbital period of 6.9 years, and it returned to perihelion again in late 2005. On its subsequent return it was recovered on July 15, 2012 by Hidetaka Sato utilizing a remotely-controlled telescope in New Mexico.

The comet is rather faint intrinsically, and I didn't look for it during either the 1998 or 2005 returns. However, the geometrical circumstances in 2012 were very favorable, with opposition occurring almost simultaneously with perihelion and with the comet's passing 0.42 AU from Earth in late September, and thus I had plans to attempt it during this return. But before I could make a first attempt, there were reports of a possible outburst in early September, and when I saw it on the evening of September 10 -- just a couple of hours after I had added the previous comet -- I easily saw the comet as a diffuse, somewhat condensed glow of magnitude 12 1/2. It maintained this appearance for the next couple of weeks, although starting to show the beginnings of a stubby tail, however I then began to read reports of a second outburst. Despite moonlight, on the evening of September 24 it was easily visible as a small and condensed object of 10th magnitude, and with a distinct tail a few arcminutes long.

Throughout most of October Comet Hergenrother was a rather striking object telescopically, with a total brightness close to magnitude 9 1/2, and exhibiting a rather condensed coma and an obvious tail slightly less than ten arcminutes long. (I tried, without success, to see the comet in binoculars.) On the 23rd it passed 45 arcminutes east of Comet Catalina C/2012 J1 (no. 508), although this event took place during bright moonlight and I didn't see it. By the beginning of November the comet had faded to about 11th magnitude (although still exhibiting the condensed coma and distinct tail), but when I saw it for the last time on the evening of December 1 it appeared as little more than a vague, ill-defined glow of magnitude 12 1/2.

512. COMET LEMMON C/2012 F6          Perihelion: 2013 March 24.52, q = 0.731 AU

I spent most of the first half of November 2012 in Cairns, Queensland, Australia in preparation for the total solar eclipse that took place on the morning of November 14. I had received a research grant from the American Public University System (where I teach) to search for any Kreutz sungrazing comets that might be near the sun during totality (a project I conducted in collaboration with the SOHO team), and also to give a series of talks to various schools throughout northern Queensland. Because of the personal circumstances I alluded to in an earlier entry, the trip was not as enjoyable as it otherwise might have been, although the people I worked with were very friendly and helpful, and the students were great (including the two high school girls who wanted to know if I thought they spoke with an accent!) The weather was a bit touch-and-go for the eclipse (which took place not too long after local sunrise), but the clouds broke a few minutes before totality and those of us assembled were able to see it. (The photo at right is a wide-field view of totality I took from our observing site at Palm Cove.) As things worked out, there were no comets near the sun during totality, although one did begin to appear in the SOHO coronagraphs later that day.

The first addition to my comet tally after my return from Australia was this object, which had been discovered on March 23, 2012, by the Mt. Lemmon survey based in Arizona. Although the comet's relatively small perihelion distance did raise some attention, it seemed to be quite faint intrinsically (being as faint as magnitude 20 or 21 at discovery), and there seemed no reason to believe it would become especially bright or notable. However, after my return I began to read reports that suggested it might be quite a bit brighter than expected, and on the morning of November 24 I successfully observed it near magnitude 11 1/2. I managed to obtain a handful of additional observations over the next month and a half as it traveled almost due southward; my last observation before it dropped below by southern horizon came on the morning of January 6, 2013, when it was at a declination of -42 degrees, and was faintly visible in binoculars at 9th magnitude.

Traveling in a steeply-inclined orbit (inclination 83 degrees), the comet rapidly entered southern circumpolar skies, and passed three degrees from the south celestial pole on February 5, around which time it was also nearest Earth (0.98 AU). During this period it was widely reported by observers in the southern hemisphere as being visible to the naked eye at around 5th magnitude; in fact, it was simultaneously naked-eye visible along with Comet PANSTARRS C/2011 L4 (no. 504). (Indeed, I have seen several dramatic wide-field images which show both comets.) Unlike the other comet, Comet Lemmon was not especially dust-rich, and thus never developed much of a dust tail; it did, however, develop a rather structured ion tail a few degrees in length.

The comet then began traveling almost due northward (passing five degrees west of the Small Magellanic Cloud in mid-February) and was still close to 6th magnitude when it went through conjunction with the sun (28 degrees south of it) during the latter part of March. It then began emerging into the morning sky, although its location south of the sun limited observations to the southern hemisphere for the next few weeks. Finally, though, it had traveled far enough north to be accessible from the northern hemisphere, and I first saw it on the morning of May 4, when it was easily visible in binoculars and appeared perhaps slighty brighter than 7th magnitude.

Comet Lemmon continued traveling northward after that, following almost the exact same path through the constellations that Comet PANSTARRS had followed two months earlier. It remained close to 7th magnitude throughout May and into early June, telescopically exhibiting a rather faint and featureless tail about half a degree long (which I also glimpsed in binoculars on a couple of occasions). It has faded steadily since then, with the tail remaining faintly detectable for some months thereafter; by the latter part of October the comet had faded to 13th magnitude and I could no longer see the tail. I am probably close to being finished with it.

513. COMET 273P/PONS-GAMBART P/2012 V4          Perihelion: 2012 December 19.67, q = 0.810 AU

At the end of November 2012 I noticed on the Minor Planet Center's Near-Earth Object Confirmation Page an object that had apparently been discovered in images taken with the Solar Wind ANisotropies (SWAN) ultraviolet telescope on board the SOHO spacecraft. (I would subsequently learn that it had been detected by American researcher Rob Matson in SWAN images beginning November 7.) On the evening of November 30 I detected the SWAN object as an obvious comet of magnitude 9 1/2, located very low in my southwestern sky after dusk.

As orbital calculations for the new discovery proceeded it became apparent that the comet's orbit bore a striking resemblance to that of a comet discovered in June 1827 by the great French comet hunter Jean Louis Pons and by fellow French astronomer (and director of the Marseille Observatory) Adolphe Gambart. Comet Pons-Gambart was a faint naked-eye object of 5th or 6th magnitude, and it was later determined to be periodic, with the best calculations indicating an orbital period of 57.5 years, although this was considered uncertain by about ten years. The identity between Comet Pons-Gambart and the new SWAN comet was soon positively established, but calculations then began to show that the calculated period for Comet Pons-Gambart was significantly in error; it has now been determined as being 188 years, indicating that this is the first return since the original discovery in 1827, and that it had not been missed on a couple of intervening returns as had long been believed.

The viewing geometry for the comet's 2012 return was significantly less favorable than that in 1827, with the comet's being on the far side of the sun, and in conjunction with it (14 degrees north of it) in early January 2013, less than two weeks after perihelion passage. I managed to obtain one more observation in the evening sky (on December 7) before conjunction, and then did not see it again until after it had emerged into the morning sky, on January 21 when it appeared close to 10th magnitude. It faded steadily from that point, and appeared near 13th magnitude when I last saw (in somewhat poor sky conditions) on the morning of March 22. I was unable to see anything convincing when I tried for it again three weeks later.

In a book that I wrote in 1999 and 2000 about cometary science and observations during the 20th Century but which was never published -- a long story -- I speculated a bit about Comet Pons-Gambart. During the 1970s two Japanese astronomers, Shigeru Kanda and Ichiro Hasegawa, had independently suggested that this comet might be identical to a comet observed from China and Germany during the year 1110. Under the assumptions that the two comets were indeed identical, and that it had made 12 returns between 1110 and 1827 (giving an approximate orbital period of 60 years, well within the range of uncertainty), I "predicted" it might return again sometime around 2006 or 2007. It is now clear, of course, that both assumptions I made were incorrect: as indicated above, the orbital period is much longer than this, and the 1110 comet could not have been Comet Pons-Gambart. Thus, the fact that my "prediction" was only a few years off is nothing more than coincidence.

514. COMET 262P/McNAUGHT-RUSSELL P/2012 K7          Perihelion: 2012 December 4.48, q = 1.280 AU

While most of Rob McNaught's comet discoveries have come about as a result of his participation in the Siding Spring survey, several of them came via an earlier photographic survey program at Siding Spring that pre-dated the current CCD-based survey. Rob discovered this particular comet in December 1994 on a photograhic plate taken by Kenneth Russell (who himself discovered several additional comets while at Siding Spring); it was reported as being about 17th magnitude, and was found to be about three months past perihelion passage. Under ordinary cirumstances I might have nevertheless attempted it, but I was going through a period of "displacement" at the time and never was able to do so.

The comet was found to be periodic, with a current orbital period of 18.25 years. It was recovered on May 29, 2012, by Giovanni Sostero, Nick Howes, and Ernesto Guido, who utilized the 2-meter Faulkes Telescope North on Haleakala in Hawaii; this recovery was confirmed the following morning by Erik Bryssinck utilizing a remotely-controlled telescope in New Mexico. The geometry of the 2012 return was somewhat better than that in 1994, with the comet's passing 0.84 AU from Earth in mid-November, and I suspected that visual observations might be possible.

I made my first attempt on the evening of December 1, and saw it as a rather diffuse object of magnitude 12 1/2. I followed it for the next two months, and it reached a peak brightness near magnitude 11 1/2 in early January 2013. Although it was still close to this brightness when I saw it for the last time on the evening of February 1, the coma had by then grown quite vague and diffuse, and I was unable to see the comet when I next tried for it a little over a week later.

515. COMET LINEAR C/2012 L2          Perihelion: 2013 May 9.32, q = 1.509 AU

I mentioned in the entry for Comet LINEAR C/2012 K5 (no. 510) that the LINEAR program in New Mexico discovered four comets during a 17-day period in May and June 2012; this was the third of those comets, which LINEAR first detected on June 1. It was a faint object of 19th magnitude at the time, and located in northern circumpolar skies at a declination of +68 degrees. From that point it traveled northward, and it passed within 15 arcminutes of the north celestial pole on November 16, although it was still far too faint for visual observations at that time. Following this passage by the pole it remained in northern circumpolar skies for the next several months as it slowly brightened.

I first attempted the comet in early December, but didn't see anything convincing. When I next tried for it on the evening of January 2, 2013, I easily saw it as a small and relatively condensed object near magnitude 13 1/2. It brightened steadily over the next few months as it moved over into the northwestern evening sky and traveled southward, being about 12th magnitude in February, 11th magnitude during March, and it peaked near magnitude 10 1/2 in early April. It was still near this brightness when I last saw it on the evening of April 28, however by then it was sinking very low in my western evening sky. Observers in the southern hemisphere were able to follow it for about another month, and according to the reports I've read it seemed to have faded about a half-magnitude before it disappeared into their evening twilight.

516. COMET LINEAR C/2012 L1          Perihelion: 2012 December 25.41, q = 2.262 AU

This was the second of the four comets that the LINEAR program in New Mexico discovered during the 17-day period in May and June 2012; as was the case with the above comet, LINEAR's discovery of this one also took place on June 1. (The two comets were 22 degrees from each other, and the respective discovery images were taken barely over an hour apart.) Like the above comet, this one remained in northern circumpolar skies for some time thereafter, passing less than 1 1/2 degrees from the north celestial pole on December 18.

After an unsuccessful attempt in early December, I tried again on the evening of January 2, 2013 -- half an hour after I first observed the above comet -- and suspected a very faint, small and condensed object slightly fainter than 14th magnitude. I was able to verify this suspected observation when I followed the comet for an hour two nights later. Because the comet was then near its expected peak brightness, and in fact would likely begin to fade soon, I did not look for it again.

517. COMET McNAUGHT C/2011 R1          Perihelion: 2012 October 19.62, q = 2.080 AU

Rob McNaught discovered this comet on September 3, 2011, during the course of the Siding Spring survey in New South Wales. It was reported as being about 17th magnitude, and traveling in a rather steeply-inclined retrograde orbit (inclination 116 degrees) it slowly brightened as it traveled southward, and I attempted it on a handful of occasions in late 2011 and early 2012 before it disappeared into evening twilight. There were a couple of times when I actually had an extremely faint suspect for the comet, but I wasn't able to verify this; had I been able to do so, this conceivably could have been my 500th comet for "Countdown."

The comet was in conjunction with the sun (45 degrees south of it) shortly after mid-April 2012, and thereafter emerged into the southern hemisphere's morning sky. For the next several months various observers in the southern hemisphere consistently reported its brightness as being between 11th and 12th magnitude, and meanwhile it entered southern circumpolar skies during July and reached a peak southerly declination just north of -72 degrees in mid-August.

Comet McNaught was again in conjunction with the sun (31 degrees south of it) in early November, and thereafter emerged again into the morning sky as it slowly climbed northward. I obtained my first sighting on the morning of January 18, 2013, when it was located at a declination of -30 degrees 5 1/2 degrees southwest of the bright star Antares; it appeared as a small and moderately condensed object of magnitude 13 1/2. This observation came just a few days after a massive bushfire had swept through Siding Spring Observatory; while Rob and his loved ones were OK, he sadly lost his home in the fire, and I felt that perhaps this observation of his comet gave me a little bit of solidarity with him.

The comet continued traveling almost due northward (passing three degrees west of Antares in early February) and also brightened somewhat, appearing near magnitude 12 1/2 around the time it went through opposition in late April. It also began to grow more and more diffuse, and when I last observed it in mid-May it appeared as just a vague, diffuse 13th magnitude glow.

518. COMET BRESSI C/2012 T5          Perihelion: 2013 February 24.06, q = 0.323 AU

Although the Spacewatch program in Arizona has discovered numerous comets since its initial comet discovery in late 1991, almost all of its comets have been very faint, and it has had an almost negligible impact on my comet tally; prior to this comet I had observed only two Spacewatch-discovered comets (Comet Spacewatch C/1997 BA6 (no. 256) and the Centaur comet 174P/Echeclus P/2000 EC98 (no. 384)), and there are only three others that I had even attempted. Terry Bressi discovered this comet on October 14, 2012, during the course of the Spacewatch program, and its small perihelion distance called attention to it almost right away; however, its faintness (18th magnitude) at the time of its discovery suggested that it was a small and dim comet intrinsically, and the consensus among comet astronomers was that it would probably disintegrate as it passed through perihelion.

Comet Bressi did neverthless brighten as it approached perihelion, and I made a couple of unsuccessful visual attempts during the first half of January 2013. However, late that month came reports that the comet had undergone a distinct outburst, and on the evening of January 27 despite low altitude and very bright moonlight I clearly saw "something" in the expected position, although it was difficult to tell much about its brightness or appearance. Three nights later, in a dark sky the comet was a relatively easy object of 11th magnitude, with a moderately condensed coma that appeared somewhat extended in the direction of a tail that was evident on CCD images taken around that time.

After that Comet Bressi dropped below my southern horizon, however observers in the southern hemisphere were able to follow it for another week or so before it entered evening twilight. According to the reports I've read the comet continued to brighten, to between magnitudes 9 and 9 1/2, however it also appeared to grow more diffuse as it was doing so. After perihelion it emerged into the morning sky, and I made one brief attempt for it in mid-March (as it was passing by the globular star cluster M15) but didn't see anything. I've seen one CCD image taken around this time which seems to show a very faint object in the comet's position, but later images have shown nothing, suggesting that the comet did indeed disintegrate as it passed through perihelion, just as expected.

519. COMET 63P/WILD 1          Perihelion: 2013 April 10.78, q = 1.950 AU

I discussed the career of Swiss astronomer Paul Wild in one of the "Countdown" entries. This comet, which he discovered in April 1960, was the second of his seven comet discoveries, and the first of his four periodic comets. It has a period of 13.2 years, and was recovered in 1973, missed at the unfavorable return in 1986, and recovered again when it passed through perihelion in late 1999. I followed it for three months at that return (no. 276), during which it became slightly brighter than 13th magnitude; it has the interesting distinction of being the last comet I added to my tally during a year which began with "1."

The comet's 2013 return was a rather favorable one, being somewhat similar to that of the discovery return in 1960. It was recovered on September 17, 2012 by Otabek Burhonov at Majdanak Observatory in Uzbekistan. When I first attempted it on the evening of February 1 I was able to detect it as a small, condensed, and extremely faint object slightly fainter than 14th magnitude. It brightened fairly rapidly from that point as it approached perihelion and as it went through opposition during the latter part of February, and it was close to magnitude 12 1/2 by early March. The comet maintained something close to this brightness for the next two months although it gradually grew more diffuse, and after viewing it near 13th magnitude in early May I suspected I was about done with it.

At mid-month, however, came reports of an apparent small outburst, and in fairly bright moonlight on the evening of May 16 I was able to see it as a somewhat condensed object of magnitude 12 1/2. After the moon had cleared the evening sky I saw it again on the evening of May 29, when it appeared as little more than a vague, diffuse object of magnitude 14; I did not look for it again after that. There were subsequent reports of another apparent outburst in late July, however by that time the comet was too low in my southwestern evening sky to attempt any observations.

520. COMET McNAUGHT C/2009 F4          Perihelion: 2011 December 31.89, q = 5.455 AU

Rob McNaught discovered this comet as long ago as March 19, 2009, during the course of the Siding Spring survey in New South Wales; it was the second of three comets he discovered within a span of two nights. It was very distant at the time, being located 8.96 AU from the sun, and with its large perihelion distance would obviously remain far from the earth and the sun; furthermore, it was already at a declination of -23 degrees, and its steeply inclined orbit (inclination 79 degrees) would keep it deep in southern skies throughout most of its appearance. I attempted it on a handful of occasions around the time of its opposition in May 2010 (when it was at a declination of -48 degrees and thus not too far above my southern horizon) but never saw anything convincing.

Comet McNaught remained south of declination -50 degrees from mid-October 2010 through the end of 2012, and south of declination -70 degrees from the beginning of March 2011 until the same time a year later; it passed within 1 1/2 degrees of the south celestial pole in mid-December 2011, shortly before perihelion passage. Observers in the southern hemisphere consistently reported it as being between 13th and 14th magnitude throughout this time, and I listed it under the "Southern Hemisphere Only" section of the "Countdown" update page while "Countdown" was going on.

I knew I would have one more opportunity to catch the comet in early 2013, after it had traveled far enough north to be accessible from my latitude, however by that time it would be low in the southwestern sky and the observing "window" would be fairly brief. I made a handful of attempts during the first half of January, when its declination was between -49 degrees and -47 degrees, but never saw anything convincing. After the late January full moon I tried again at the beginning of February and still didn't see anything, but on the evening of February 5 (when the comet's declination was -42 degrees) I suspected an extremely faint "something" at the comet's expected position, which after subsequent observations on the evenings of the 7th and 8th I was able to verify as indeed being the comet. I obtained a couple of additional observations during the first half of February and one more at the beginning of March (by which time the comet had traveled north to declination -37 degrees but was getting quite low in the southwest after dusk); on all occasions it appeared as little more than an extremely faint object slightly fainter than 14th magnitude, right at the very limit of vision.

          

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