|451. COMET 77P/LONGMORE Perihelion: 2009 July 7.85, q = 2.310 AU
Half an hour after I had verified my "halfway" comet on the evening of February 25, I got started on the second half of "Countdown." Although both comets have similar orbital periods and were discovered within a few years of each other -- and, curiously, were only two degrees from each other in the sky when I saw them -- my observational history of them is dramatically different; whereas I have just picked up my "halfway" comet on the fifth consecutive return, this is a comet that I have never before attempted, let alone observed.
The comet was originally discovered in June 1975 by Andrew Longmore during the course of the Southern Sky Survey (a southern hemisphere version of the Palomar Sky Survey) that was being conducted from Siding Spring Observatory in New South Wales. Although it was faint and poorly observed, the observations obtained then were sufficient to show that it had passed perihelion late the previous year and that it was traveling in a short-period orbit of almost exactly 7.0 years. It has been recovered at every subsequent return, however that orbital period always has brought it to perihelion when it was on the far side of the sun from Earth, and thus it has always remained a faint and distant object. Finally, a distant approach to Jupiter (1.6 AU) in 1999 brought it out of this continuously unfavorable alignment, in the process shortening the orbital period to the current 6.83 years and decreasing the perihelion distance from 2.4 AU to the current value. The 2002 return was still fairly unfavorable, but by the current return the viewing geometry had improved enough to make visual observation attempts worthwhile. The comet was recovered on January 7, 2008 by Francois Kugel at the Observatoire Chante-Perdrix at Dauban, France.
And as fate would have it, I picked it up on my very first attempt. The comet appeared as a very faint object near magnitude 14 1/2, being located in the eastern regions of the Virgo galaxy cluster, just one degree northwest of the galaxy M90. I successfully confirmed it by detecting a slight westward motion over the course of the next hour, then observing it again three nights later.
Just like the earlier comet, P/Longmore spends the next month crossing westward across the Virgo cluster, and is at opposition during the third week of March. It then begins traveling southward and crosses into eastern Leo during April; it eventually crosses back into Virgo in early June. The comet will probably remain quite faint, brightening by perhaps at most half a magnitude by April, and will probably have faded beyond the range of visual detectability by June or July.
Although P/Longmore will probably never become bright, the next two returns (in 2016, with perihelion in mid-May, and in 2023, with perihelion in early April) are both slightly more favorable than this year's, and it should become slightly brighter than it does this time around.
This "halfway" part of "Countdown" comes at a rather interesting time in my life. The major life changes I've been hinting at for some time are well underway and should be coming to fruition with the not-too-distant future; I'll discuss those at the appropriate time. Meanwhile, I am beginning an on-line teaching job with the American Military University (part of the American Public University System) this week; I've been in preparation and training for this position for the past few weeks. I'm also in the midst of a series of public and school presentations I've been conducting as part of the New Mexico State Parks Department's "Reach for the Stars" program, for which I successfully obtained funding last year; I've recently returned from a trip to Carlsbad, New Mexico, where I talked to several school classrooms and at Brantley Lake State Park. I'm giving this entire series of talks right now to take advantage of the current naked-eye appearance of Comet Lulin C/2007 N3 (no. 432).
And meanwhile, although the comet tally additions have been coming pretty fast and heavy over the recent past, this will more than likely slow down during the near future. Among known comets, there is a faint periodic one that I might possibly add within the next month or so, but other than that there aren't any that I have a reasonable expectation of adding to my tally before about the middle of this year. It's always possible, of course, that there will be some new discoveries, as well as the possibility that a faint comet will unexpectedly outburst (as Comet 33P/Daniel (no. 449) did recently), but unless there is a flurry of such activity over the next few months my rate of adding comets will probably slow quite dramatically for a while.
In this era of the comprehensive sky surveys it is rather unusual for a bright comet to appear unexpectedly; most of the bright inbound long-period comets are discovered weeks, sometimes months, before they are bright enough to detect visually. Still, an occasional unexpected bright comet does appear from time to time, as what happened with this one.
The comet was discovered on CCD images taken March 14, 2009 by Japanese amateur astronomer Koichi Itagaki, who among many other astronomical discoveries found the comet (P/2008 R6) last year that was soon identified with the long-lost periodic comet now known as 205P/Giacobini (no. 438); his discoveries are recounted in that object's "Countdown" entry. (This is his first comet discovery to which his name has been assigned.) I noticed it as a fairly bright object on the Minor Planet Center's Near-Earth Object Confirmation Page, and when I turned my telescope that evening to the expected position I immediately saw a 10th-magnitude comet (although some ten arcminutes south of the predicted location). Unfortunately, I was only able to view the comet for about two minutes before clouds covered it up; within twenty minutes it was snowing! (Since this has been a dry winter here in the southern New Mexico mountains and we are now coming into fire season, no one around here is complaining about the moisture.) I had a better and less-hurried view the following night under clear skies.
According to the orbit available at this writing (still somewhat preliminary but unlikely to change by much), Comet Itagaki is traveling in a steeply-inclined retrograde orbit (inclination 127 degrees), and theoretically it could have been discovered much sooner than it actually was. For the past couple of months it has been easily accessible from the southern hemisphere and brightening, and it passed 0.65 AU from Earth shortly after mid-February. It also appeared in images taken with the SWAN ultraviolet telescope aboard aboard SOHO back to early March, and in images taken by the STEREO-A spacecraft to as far back as early February, but wasn't detected until well after the fact. At the time of its discovery it was located in northeastern Cetus (two degrees from the star Mu Ceti) and it was already fairly low in the western evening sky at an elongation of 49 degrees.
I will probably not be obtaining very many observations of this comet. At this writing it is located in south-central Aries (the elongation already having shrunk to 44 degrees) and it is traveling towards the north-northwest at approximately 1 1/4 degrees per day, thus sinking closer to the western horizon each night. Over the next couple of weeks the motion tends more westerly, and on March 31 it passes directly over the bright star Hamal (Alpha Arietis); by then it theoretically might have brightened by about half a magnitude but the elongation will have shrunk to 29 degrees. Comet Itagaki is in conjunction with the sun (just over 19 degrees north of it) shortly before mid-April and then it emerges into the morning sky by the end of that month. Although it begins to approach Earth again (passing 0.97 AU away in early July) its receding from the sun should cause it to fade fairly rapidly, probably beyond the range of visual detectability by late May or early June (during which time it will be traveling parallel to -- and slightly north of -- the northern "boundary" of the "Great Square" of Pegasus).
UPDATE: This comet appears to be an intermediate-period object; according to orbital calculations published on March 20 (which must still be regarded as somewhat uncertain) Comet Itagaki has an orbital period of approximately 250 years. It would have last passed perihelion sometime around the mid-18th Century, but so far there do not seem to be any comets observed around that time that can be identified with it. Depending upon what time of the year it passed perihelion it may well have been detectable with the telescopes and observing techniques of that era, so it is conceivable that, once a more precise orbit can be calculated, we may yet be able to identify Comet Itagaki with a comet that was seen during that period.
UPDATE: As I expected, I picked up Comet Itagaki in the morning sky around the end of April, as a somewhat condensed object between magnitudes 9 1/2 and 10. If it fades "normally" it will probably initially fade pretty rapidly (perhaps to 12th magnitude by early June) and remain visually detectable until perhaps sometime in July.
The orbital period of approximately 250 years that I mentioned above still seems to be holding based upon the most recent calculations, but there does not seem to have been any comets that were detected in the mid-18th Century that appear to be identical with it.
It figures that a relatively bright new comet would be discovered while I was on an overseas trip and thus not in any kind of position to observe it. On April 2 I departed the U.S. for a week's stay in Lebanon, where among other things I gave a series of presentations to students at the Houssam Hariri High School in the historical city of Sidon and participated in a couple of "100 Hours of Astronomy" events that are part of the International Year of Astronomy. In addition to being overseas at the time of the comet's discovery, the recovery from the long trip back (together with a vicious cold that struck with a vengeance in the process), bright moonlight, and a storm system that moved through southern New Mexico all conspired to delay my first sighting of it.
The comet was discovered by American researcher Rob Matson in a series of images (beginning March 29) taken with the Solar Wind ANisotropies (SWAN) ultraviolet telescope on board the SOlar and Heliospheric Observatory (SOHO) spacecraft that was launched in late 1995. Although it wasn't primarily designed for this purpose, SWAN has proven to be an effective comet detector, since the majority of comets coming into the inner solar system are surrounded by large clouds of hydrogen that shine quite strongly in the ultraviolet. (This was first observed in early 1970 when the Orbiting Astronomical Observatory 2 (OAO-2) satellite detected such a cloud around Comet Tago-Sato-Kosaka 1969g -- the first comet observed from space, and incidentally my first comet as well.) The first two "SWAN comets" were C/1997 K2 and C/2000 S5, both of which were not noticed until some time after the fact and which were never seen from the ground; the first "real-time" SWAN comet was C/2002 O6, which I played a major role in confirming (no. 314). C/2009 F6 is the seventh real-time SWAN comet, and I've managed to observe all of these.
Once ground-based confirmation of the comet was obtained and an initial orbit calculated, it was found to be identical to a possible comet that had been reported by Korean astronomer Dae-am Yi on CCD images taken March 26. This is the first comet discovery from a Korean observer in modern times (although several comets had been recorded in Korea during antiquity).
Technically the comet is currently a morning object, although its present location allows it to be observable both in the morning and evening skies. After the various delays I mentioned earlier, I finally succeeded in observing it on the evening of April 11 (the night before my son Tyler's 17th birthday). It appeared as a vague diffuse object of 10th magnitude, very low in the northwestern sky after dusk and located just half a degree southeast of the star Alpha Cassiopeiae. It is traveling in a steeply-inclined orbit (inclination 86 degrees) and for the time being is moving almost directly eastward, being at its farthest north point (declination +56.6 degrees) on April 17 and then in conjunction with the sun (45 degrees north of it) four days later. Afterwards the comet is best viewed in the evening sky, traveling southeastward through Perseus along the galactic equator; because the elongation is small and continues getting smaller it will likely not be an easy object to observe. Since it was nearest Earth (1.76 AU) early this month it is probably about as bright now as it is going to get.
The comet's elongation drops below 20 degrees at the beginning of June, and it is again in conjunction with the sun (just two degrees away) at the beginning of July. It emerges into the southern hemisphere's morning sky around the middle of August, and theoretically may still be detectable visually as a faint object, although it probably won't remain visible for long.
I thus probably won't be obtaining many observations of this comet. This seems to be typical of the SWAN comets in general, which tend to remain at small elongations and not get especially bright. Of all the previous six real-time SWAN comets, only two -- one of these being C/2006 M4 (no. 396), which underwent an outburst and briefly became a naked-eye object of magnitude 4 1/2 -- have I followed for even as long as a month, and this one will probably be fairly short-lived as well.
I mentioned in the previous entry that Comet Tago-Sato-Kosaka 1969g -- my very first comet -- was also the first comet ever observed from space. It was probably inevitable that there would someday come a time when comets would begin being discovered from space. The first space-based comet discovery was of Comet 1979 XI (which appeared in August of that year, although it wasn't formally announced until two years later), and which was made with the SOLWIND coronagraph aboard the American Department of Defense satellite P78-1. SOLWIND would go on to detect nine additional comets over the next few years before P78-1 was intentionally destroyed as part of an Anti-Satellite (ASAT) test in 1985; all but one of these ten comets were Kreutz sungrazers, and none of them were detected from the ground.
Following SOLWIND, the InfraRed Astronomical Satellite (IRAS) discovered six comets during its ten-month operational lifetime in 1983; one of these was the very close Earth-approaching Comet IRAS-Araki-Alcock 1983d (no. 56), and in addition to this one I observed three others, two of these being short-period objects that I've also since seen on subsequent returns. Then there was the Solar Maximum Mission (SMM) satellite, which discovered ten Kreutz sungrazers during the late 1980s; as with the SOLWIND comets, none of these were seen from the ground. The champion comet-discovering entity of all time is the SOlar and Heliospheric Observatory (SOHO) spacecraft, a joint NASA/ESA mission that was launched in late 1995 and that observes the sun continuously from the L1 Lagrangian point one million miles (1.6 million km) directly sunward of Earth. Among SOHO's instruments are two coronagraphs that have proven especially adept at detecting comets near the sun, and as of now these have detected over 1600 comets. The vast majority of these are Kreutz sungrazers or are members of other recognized "groups;" only a relatively small percentage of these are "non-group" objects. (The only SOHO comet to become visible from the ground was the "non-group" object C/1998 J1 (no. 242), which became visible to the naked eye from the southern hemisphere; I managed to obtain a few observations of it while visiting Australia during that time.) There is also the SWAN ultraviolet telescope aboard SOHO, which has discovered nine comets (all but two of these being "real-time" discoveries) including the previous entry.
The newest comet-discovering spacecraft are the twin components of the Solar TErrestrial RElations Observatory (STEREO) mission. STEREO consists of two identical spacecraft orbiting the sun (one ahead of Earth, the other lagging behind) that are designed to provide three-dimensional, or stereoscopic, views of the sun from ever-widening vantage points. The two STEREO spacecraft were launched together in October 2006, and each is equipped with a bevy of scientific instruments, including two coronagraphs and two wider-field "Heliospheric Imagers." Since early last year twenty STEREO comets (plus the recovered comet 210P/Christensen (no. 446)) have been discovered in images taken with these instruments; all but two of these have been Kreutz sungrazers.
The second of these non-Kreutz comets, and the first (and, so far, only) STEREO comet to be seen from the ground, was discovered by Chinese astronomer Jiangao Ruan on a series of images taken with one of the Heliospheric Imager instruments aboard the STEREO "B" spacecraft (the one lagging behind Earth) beginning on April 3. A preliminary orbit calculation by Brian Marsden at the Minor Planet Center allowed Japanese amateur astronomer Ken-ichi Kadota to capture images of it on the morning of April 9 and thus allowed for a more accurate orbit to be calculated. By the time all of this was accomplished the moon was full, and I had to wait several days for the morning sky to darken enough to make an attempt for the comet; I finally did so on the morning of April 16, when the moon's phase was at third quarter. In the moderately brightened sky I was able to observe the comet as a somewhat condensed 11th-magnitude object low in the southeastern sky around the beginning of dawn.
Comet STEREO is presently located in eastern Aquarius about eight degrees southeast of the "water jar" asterism, and is traveling towards the southeast. This continued southward motion, combined with the sun's traveling northward, conspire to make the comet an increasingly difficult object to observe from the northern hemisphere; by early May it will be rising around the beginning of twilight from my latitude, and I will thereafter lose it. The southern hemisphere, meanwhile, should enjoy increasingly better views, as the comet passes through Sculptor, Phoenix, Eridanus, Horologium, and Reticulum, entering southern circumpolar skies by the second week of June and reaching a peak southerly declination of -61.9 degrees at the time of the June solstice before being in conjunction with the sun (85 degrees to the north) a week later. It is nearest Earth (1.05 AU) at the end of May and, if it exhibits a normal brightness behavior, reaches a peak brightness about half a magnitude brighter than its current value around mid-May before fading by perhaps a full magnitude toward the latter part of June. After that it begins traveling northward, although staying south of declination -50 degrees, and should fade from view by sometime in July or August.
Those of us who have been involved in cometary astronomy for a long time had long suspected that we were detecting only a fairly small percentage of the comets that come into the inner solar system. These suspicions were verified once the comprehensive sky surveys started coming on-line during the latter part of the 1990s, and the number of comets being discovered has climbed quite rapidly. In addition to the much higher number of long-period comets being discovered, the surveys also detected a population of (intrinsically) very faint short-period comets that until then had eluded being seen. Many of these comets have absolute magnitudes (the apparent magnitudes they would have if located 1.0 AU from both the sun and Earth) in the range of 16 to 19 -- much, much fainter than the traditionally known short-period comets.
One of these very dim periodic comets was discovered in March 2004 by the LINEAR program based in New Mexico and initially was thought to be an Apollo-type asteroid, and in fact was assigned the designation 2004 CB until later observations revealed it to be a small comet. It was never observed to be brighter than about 16th magnitude, and calculations revealed it had an orbital period of just over 5.0 years. At the next return it was recovered on December 4, 2008 by Gary Hug at his private Sandlot Observatory in Scranton, Kansas, and subsequently assigned the designation 209P.
The geometry at the present return is quite favorable, and the comet passed 0.26 AU from Earth on April 10. I began making visual attempts for it in late February, but up through the beginning of April my attempts were all unsuccessful. However, on the morning of April 22 (my first attempt after the April full moon) I was able to detect it as a very tiny and faint object slightly fainter than 14th magnitude, traveling fairly rapidly through the surrounding star field.
At the time of this initial sighting the comet was located in southwestern Pegasus, just 1 1/2 degrees west of the star Enif (or Epsilon Pegasi). It is currently traveling towards the south-southeast at the rate of 1.7 degrees per day, and since it is receding from both the sun and Earth I would expect a fairly rapid fading. At most I will probably be able to obtain only one or two more observations of it before it fades beyond my range of detectability.
Comet 209P has an interesting treat in store for us at its next return, in 2014 (perihelion in early May). On May 29 of that year the comet passes only 0.055 AU from Earth, one of the closest cometary approaches to Earth ever recorded. At the time of its closest approach it will be in the evening sky, traveling southward through the constellations of Leo, Sextans, and Crater at ten degrees per day. (Conveniently, this will take place right around new moon.) Based upon the brightness I've observed at the current return, when it makes its passage by Earth five years from now it still won't be any brighter than about 11th magnitude -- which goes to show just how tiny and dim some of these recently-discovered periodic comets are.
It sometimes happens that a comet is easily detectable to my comet-watching friends in the southern hemisphere but is inaccessible from my latitude, and I have to sit and wait patiently for it to travel far enough northward to be visible to me. Such has been the case with this particular comet, which was discovered back on August 27, 2008 by Gordon Garradd during the course of the Siding Spring survey based in New South Wales. We've already encountered Gordon's name previously in "Countdown," and this is the third comet discovery of his that I have seen; overall this was his 11th comet discovery, of 12 so far at this writing.
At the time of its discovery Comet Garradd was a dim, 19th-magnitude object located in the southern constellation Phoenix near a declination of -48 degrees. It was followed with large telescopes for the next three months before disappearing into evening twilight, and then picked up in the morning sky near the end of March. Shortly after mid-April observers in the southern hemisphere began to report that it was almost as bright as 9th magnitude -- several magnitudes brighter than originally expected. While there was some initial speculation that this might be due to an outburst, the comet has not only maintained this brightness since that time but has actually become brighter; the reports I've been reading from the southern hemisphere over the past two to three weeks have all been been pretty consistent at placing its brightness between 7th and 8th magnitude.
Meanwhile, all I could do was read these reports and wait my turn as the comet traveled through southern circumpolar skies, reaching a peak southerly declination of -67.8 degrees during the third week of May shortly before it went through opposition. (I've been listing it under the "Southern Hemisphere Only" section of the "Countdown" update page throughout this time.) While it did start to travel northward after that, I've had to wait for the bright moon to begin clearing the evening sky before making any kind of attempt. Finally, in what might be a bit of impatience, and also because I had experienced a significant personal disappointment earlier that day and I needed the emotional therapy that observing gives me, I went out on the bright moonlit evening of June 7 and managed to locate the comet when it was at a declination of -47 degrees and located 2 1/2 degrees east of the bright globular star cluster Omega Centauri; in the very bright sky I could tell that the comet was "there" but not much else. After two days of cloudy and rainy weather I was able to view the comet in a dark sky on the evening of the 10th; it was an easy object in binoculars, of magnitude 7 1/2 with a coma 10 arcminutes across. At the time it was located just less than a degree north of the bright galaxy NGC 5128 ("Centaurus A") and the two objects were simultaneously visible in the same binocular and low-power telescopic fields.
Comet Garradd is traveling in a fairly steeply-inclined retrograde orbit (inclination 141 degrees), was nearest Earth (0.94 AU) at the beginning of this month, and will be at perihelion in a week and a half; it is probably about at its peak brightness, although of course one can't know for sure one way or the other right now. It is traveling northward fairly rapidly for the time being (currently at almost two degrees per day, although this slows down to one degree per day by the end of June), and is now located in northern Centaurus; during the second half of this month it crosses eastern Hydra and eastern Corvus before entering western Virgo during the second week of July (passing one degree west of the galaxy M104 in the process), where it remains for the next several months. Theoretically the comet should be accessible from my latitude until sometime in August, although by then it will be quite low in the western sky after dusk, and depending upon its future brightness behavior I might lose it well before that time.
In addition to adding Comet Garradd to my tally, I've managed to make a couple of other noteworthy comet observations during the recent past. On the morning of June 1 I obtained my 5000th visual comet observation, the milestone observation being of Comet 22P/Kopff (no. 448), the second of three comets I observed that morning. On June 10, just after I observed Comet Garradd, I obtained an observation of Comet McNaught C/2005 L3 (no. 408); this observation took me past the two-year point for this particular comet. It becomes only the fifth comet on my tally that I've followed for more than two years, and since two of these are "returns" of Comet 29P/Schwassmann-Wachmann 1 in a sense it is only the third comet that I've been able to follow for that long a period of time.
And on the personal front . . . I've already mentioned the personal disappointment (which I choose not to share here) that I experienced this past weekend. The major changes in my personal life that I've been alluding to for over a year now are still underway but are taking much longer to happen than I had originally envisioned, and they're likely to take a few more months before finally coming into fruition. On the other hand, I'm keeping quite busy; my teaching load with the American Military University is increasing (I'm now teaching two staggered-term courses, and more are in the works), I'm working with the New Mexico Museum of Space History in designing curricula for their summer Shuttle Camp program and as a part of that I'm teaching classes there two days a week, and I've got more "Reach for the Stars" presentations (under my contract with the New Mexico State Parks Department) coming up in a couple of weeks. Meanwhile, just a few days ago I learned that I was named the New Mexico state finalist in the 2009 "Above and Beyond" Awards program (the civilian equivalent of the Congressional Medal of Honor); to a fairly large degree, this is due to the work I've done in developing Earthrise and pursuing its overall mission, and it is quite gratifying to receive some high-level recognition for these efforts. (I've posted the finalist certificate here.) In any event, the hills and valleys of life continue on as the comets come and go.
UPDATE: After being in conjunction with the sun in early October Comet Garradd began emerging into the morning sky during November, and I was somewhat surprised to still be able to detect it when I attempted it shortly after mid-month; it appeared as a vague and diffuse object near magnitude 13 1/2. During the last weeks of 2009 it travels northward through southwestern Bootes, crossing into southeastern Canes Venatici shortly after the beginning of 2010 and passing half a degree west of the globular star cluster M3 on January 4. Although it is currently drawing closer to Earth it is nevertheless five months past perihelion passage and thus will likely continue fading; it probably will not remain visually detectable for much longer.
Less than a week after adding the above bright comet to my tally, I'm back to adding faint ones again. But, this one should eventually become somewhat bright, and besides, it's an old friend, coming back for another visit.
The comet was originally discovered in August 1981 by Ellen Howell, at that time a student at the California Institute of Technology (or CalTech), on photographs she had taken with the 46-cm (18 inch) Schmidt telescope at Palomar Observatory in California. She has since gone on to become a professional scientist, and is presently a computer specialist at the Arecibo radio telescope in Puerto Rico; meanwhile, this would remain her only comet discovery. I can't really say I know her well, but I do recall meeting her at a couple of scientific conferences I attended in the late 1980s and early 1990s while I was in graduate school.
At the time of her discovery Ellen's comet had an orbital period of 5.9 years and a perihelion distance of 1.62 AU. It has been recovered at every subsequent return, although an approach to Jupiter of 0.53 AU in August 1990 decreased the perihelion distance to the present value of 1.4 AU and also shortened the orbital period to 5 1/2 years. At the present return it was recovered on December 30, 2008 by the Spacewatch program in Arizona. Meanwhile, in 1995 Lowell Observatory astronomer Brian Skiff -- whom we've already encountered in "Countdown" -- managed to locate 19th-magnitude images of P/Howell on both the red and blue photographic plates that were taken during the course of the first-generation Palomar Sky Survey in May 1955; at that time it had an orbital period of 6.5 years and a perihelion distance of 1.92 AU, but another Jupiter approach (0.58 AU in 1978) decreased these values to those it had at the time of its discovery.
I didn't attempt P/Howell during its discovery return, but have done so at every subsequent one. I successfully observed it during its returns in 1987 (no. 103), 1998 (no. 245), and 2004 (no. 349) but failed to observe it during the relatively unfavorable return in 1993. During the present return I made my first attempts for it in mid-May, and once the moon cleared the evening sky in June I began looking for it again (despite the fact that New Mexico currently seems to be in the track of the subtropical jet stream and we've been getting waves of thick cirrus clouds which I've had to look around). I had a fairly strong suspect for the comet on the evening of June 12 and was able to verify this the following night; it appeared as a somewhat vague and diffuse glow of magnitude 13 1/2 located just a little over a degree east of the star Eta Virginis.
This year's return is quite similar to that of 1998 (when perihelion passage occurred in late September), during which I was able to follow it for six months and it reached a peak brightness of magnitude 10 1/2. It already went through opposition in early April and remains in the evening sky throughout its viewing time, traveling southeastward along the ecliptic through Virgo (passing less than two degrees north of the bright star Spica at the beginning of August), Libra, Scorpius (passing through the "head" of that constellation in late September), and Ophiuchus, then entering Sagittarius during the last week of October and Capricornus at the beginning of December. If it follows the same brightness behavior that it did in 1998 it should brighten slowly over the coming months and reach a peak brightness of perhaps 11th magnitude around the time of perihelion, and remain visible until about the end of this year.
There aren't any more close approaches to Jupiter for quite some time, and as long as I continue to actively observe comets I should be seeing P/Howell at its returns for the foreseeable future, as it alternates between morning returns (like that in 2004) and evening returns like this year's; over time both the orbital period and perihelion distance will shrink very gradually. The return in 2031 -- another evening return like this year's -- is somewhat unusual in that, around the time it is near perihelion (early September) it also passes only 0.08 AU from Mars.
The comprehensive sky surveys that began to come on-line a little over a decade ago have made the overwhelming number of comet discoveries since that time, and the conventional wisdom is that there is very little room left for the amateur astronomers who might wish to hunt comets. This hasn't been entirely true, as there continues to be a relatively small number of amateur comet discoveries (a handful of "Countdown" comets are in this group), although the majority of such discoveries are being made via CCD or digital cameras; as of this writing there hasn't been a visual comet discovery in over 2 1/2 years. This particular comet is the third amateur comet discovery this year, and somewhat interestingly, all three have been found by amateur astronomers in the Orient.
The comet was discovered by Rui Yang (of Hangzhou in Zhejiang province in China) on images taken with a digital camera on June 15 by Xing Gao (of Urumqi in Xinjiang province) in the course of the Xingming Comet Survey being conducted from Mt. Nashan. (We've encountered Xing Gao before in "Countdown," as he was one of the co-discoverers of Comet Chen-Gao C/2008 C1 (no. 426), which was found under similar circumstances.) At the time of its discovery the comet was being reported at around 14th magnitude, and it was located in Serpens Cauda 3/4 of a degree southwest of the star cluster (and Eagle Nebula) M16 (the site of the famous "Pillars of Creation" image taken by the Hubble Space Telescope). Several astronomers from around the world were able to image it over the course of the next day which allowed its discovery to be announced (along with a preliminary orbit) in pretty short order. Shortly after midnight on the night of June 16-17 I successfully observed it visually, as a small and condensed object of 13th magnitude. (It is not unusual for a comet's visual brightness to be a magnitude or two brighter than that reported photographically or digitally.)
Comet Yang-Gao is currently heading almost due northward, eventually turning more to the east over the next couple of months (remaining in Serpens Cauda that entire time). According to the most recently published orbit -- which is subject to change as more data becomes available over the next couple of weeks -- the comet passed passed perihelion almost a month ago, was nearest Earth (0.30 AU) near the beginning of this month, and will be at opposition in a little over a week. Under ordinary circumstances one would expect it to fade fairly rapidly, to beyond the point of visual detectability within about a month.
But, we're not quite sure yet what "ordinary circumstances" might mean for this comet. According to the most recent orbit, it has an orbital period of 6.40 years (a figure which is certainly subject to some change); since it seems to be relatively bright as far as recently-discovered short-period comets go, it would seem somewhat of a mystery why it wasn't found on previous returns. In fact, it should have been moderately bright and discoverable for the past few months (at least, from the southern hemisphere). It is entirely possible that the comet has undergone an outburst within the fairly recent past, in which case it might fade even more rapidly than one might normally expect; on the other hand, it is conceivable that it has recently been perturbed into a smaller, closer-in orbit as a result of a recent approach to Jupiter. (It is not unusual for such comets to be relatively bright on their first post-approach perihelion passage, since they're seeing more sunlight and solar heating than they have encountered in the past.) In any event, we should know more fairly soon as more accurate orbits start to become available and as we see what the comet does over the next few weeks.
UPDATE: Comet Yang-Gao seemed to maintain its brightness rather well for a while, although it finally faded beyond the range of visual detectability by about the middle of July. There doesn't really seem to be any reason any more to believe it had an outburst before its discovery, although it still is somewhat of a mystery why it wasn't detected earlier at this return.
The latest orbital calculations indicate an orbital period of 6.32 years. Although this still must be considered somewhat preliminary, there does not seem to have been any close approaches to Jupiter within the recent past, the closest encounter being one of 1.2 AU taking place in May 2001. The most recent return prior to the current one, in 2003 (perihelion mid-January) was relatively unfavorable and it probably isn't surprising that it wasn't discovered then; the return prior to that, in 1996 (perihelion mid-August) was somewhat better and the comet should have reached a peak brightness near 16th magnitude, but this was before the comprehensive surveys were underway.
The comet passes 0.3 AU from Jupiter in February 2013, and this increases the perihelion distance to 1.43 AU and the orbital period to 6.6 years. None of the first few returns after that are especially favorable (the best one perhaps being that of 2022, with perihelion in late March and a peak brightness near 16th magnitude), and thus the current return is likely to be the only one in which I will have been able to observe it.
During the last couple of years of the 1990s and the first few years of this decade, the overwhelming number of ground-based comet discoveries were made by the LINEAR program based in New Mexico. While LINEAR has been surpassed in more recent years by some of the newer survey programs, it still contributes a reasonable number of near-Earth asteroid discoveries as well as the occasional comet discovery (including one so far this year); as of this writing it has made 188 comet discoveries (not counting a handful of re-discovered "lost" periodic comets that did not have the name "LINEAR" assigned to them).
Many of those LINEAR-discovered comets were short-period objects that are now making their first predicted returns, and several of these (including one recent "Countdown" tally addition) have been recovered and assigned periodic comet numbers within the fairly recent past. This particular comet was first discovered by LINEAR in June 2001 but was not recognized as a comet at first and was assigned the "asteroidal" designation 2001 MD7; when re-discovered (again by LINEAR) three weeks later it was clearly seen as cometary. It has a current orbital period of 7.83 years, and was recovered this past March 17 by the team of Ernesto Guido and Giovanni Sostero in Italy together with Paul Camilleri in Australia utilizing remotely-controlled telescopes in New Mexico and in New South Wales.
I successfully observed the comet at its discovery return in 2001 (no. 297), following it for four months as it reached a peak brightness of 12th magnitude. After a couple of earlier unsuccessful attempts on this return I first picked it up on the morning of June 22, when it appeared as a slightly condensed object of magnitude 13 1/2. The viewing geometry at the current return is actually somewhat better than at the discovery return, as the comet passes 0.58 AU from Earth a few days before perihelion passage, and if it behaves similarly in brightness it should peak near 11th magnitude around that time. Comet 217P is presently located in northeastern Aquarius, and over the coming months travels almost directly eastward across southern Pisces, Cetus, northern Eridanus (where it will be located when at perihelion), and Orion (passing one degree north of the great Orion Nebula M42 in late September), remaining in the morning sky throughout that time. After being at its stationary point in early November it begins backtracking northwestward through Orion, and when at opposition shortly after mid-December will likely have faded to about 13th magnitude and be close to fading beyond visual range.
It appears that the current return of Comet 217P is the most favorable one for some time. At the next return, in 2017 (perihelion mid-July) it will be less well-placed in the morning sky, although it should still be visually detectable near magnitude 12 1/2 or 13 when near perihelion passage. The returns after that are less favorable still, although eventully we have a very good return in 2048 (perihelion just after mid-September), when it passes just under 0.40 AU from Earth and should reach 10th magnitude.
While I have been adding comets to my tally quite rapidly in the recent past -- this being my fourth tally addition since the beginning of June -- this is probably going to slow down rather dramatically; not until about September are there any known comets that I have a reasonable expectation of adding to the tally. (It is always possible, of course, that there will be unexpected new discoveries between now and then -- we've already had a fairly high number of such discoveries this year.) Meanwhile, I've been pretty busy lately; in addition to the on-line classes I've been teaching and the weekly classes I'm teaching as part of the New Mexico Museum of Space History's summer Shuttle Camp program, this past weekend I attended the formal groundbreaking ceremony at Spaceport America and then gave a series of "Reach for the Stars" presentations at Brantley Lake State Park near Carlsbad, New Mexico. Plus, in a couple of days I will finally have the long-awaited cataract surgery in my left eye. Finally, those big changes in my personal life that I've been hinting about for so long may finally be coming to pass in the not-too-distant future, and if that is the case I may have quite a bit to write about when the next tally entry comes.
UPDATE: As expected Comet 217P reached 11th magnitude around the time of perihelion passage, appearing relatively condensed and exhibiting a distinct westward-pointing tail. In mid-October, however -- a little over five weeks after perihelion -- it underwent a bit of an outburst, reaching 10th magnitude and exhibiting an appearance somewhat reminiscent of that of Comet 17P/Holmes after its enormous outburst in late 2007, wherein the above features were encased within a larger outer halo. The overall visual appearance is well shown in this CCD image taken shortly after the outburst.
July and August are normally the cloudiest months of the year here in New Mexico, as this is when our annual monsoon season is usually in full swing. Thunderstorms -- or, at least, the clouds associated with thunderstorms -- are an almost daily occurrence, and clear nights are usually few and far between. Still, we do get occcasional clear and dry spells that may last few a few days or more, and despite the normal cloudy weather July and August have been my most successful months for adding comets to my tally ever since my return to New Mexico in 1986 -- August for sheer numbers, and July for consistency; only once over the past 23 years have I failed to add at least one comet to my tally during July. (I've often considered the fact that I found it during July to be one of the most remarkable aspects of the Hale-Bopp discovery.) With the addition of this comet which, frankly, I had no expectation of seeing, I am able to maintain that remarkable July addition string for yet another year.
The comet was originally discovered in November 1889 by the prolific late 19th-Century American comet discoverer Lewis Swift (then observing from Rochester, New York), who discovered a total of 13 comets between 1862 and 1899. (The first of his discoveries was the comet now known as 109P/Swift-Tuttle, the parent comet of the Perseid meteors that reach their peak display in August, and that last returned in 1992 (no. 173).) Although the astronomers of that era were able to determine that Swift's comet was periodic, it remained lost until re-discovered in February 1973 by Tom Gehrels on photographs taken with the 1.2-meter Schmidt telescope at Palomar Observatory in California. At that time the comet was a very faint object of 19th magnitude, and calculations soon revealed that it had passed perihelion over five months earlier and was identical to Swift's lost comet, with an orbital period of 9.2 years.
P/Swift-Gehrels next returned in 1981, under geometrical circumstances almost identical to those at the time of Swift's discovery, and it reached a peak brightness near 10th magnitude. I followed it for over two months at that return (no. 48), which came at a very difficult time in my personal life; it would probably be fair to say that my observations of it (when it was the only comet then visible with the equipment I had) helped sustain me emotionally through that period. I managed to obtain a couple of observations at the following return in 1991 (no. 153) when the viewing geometry was distinctly less favorable, although my personal life was certainly happier (as I was then working on my doctoral thesis at New Mexico State University). The next return, in 2000, was very unfavorable and I didn't attempt it.
The current return isn't much better, and as I've already indicated I had no plans to attempt it. It was recovered on June 26, 2009 by Japanese amateur astronomer Ken-ichi Kadota, who over the years has proven extremely adept at picking up comets close to the horizon; at the time of its recovery the comet's elongation from the sun was only 28 degrees. Kadota reported the brightness as being 14th magnitude, which under ordinary circumstances would indicate it was worth attempting, but the small elongation, the fact that the comet was already past perihelion and also receding from Earth, and the heavier-than-average monsoon activity we've been experiencing here in New Mexico, all made me wonder if I should even bother. I finally decided that I would give it a try, but had to wait until I had decent weather conditions; I eventually did on the morning of July 30, and somewhat to my surprise saw the comet without too much difficulty as a rather diffuse object of 13th magnitude. (Incidentally, I was also finally able to make an attempt to observe the impact "scar" that recently appeared on Jupiter, but was unable to convince myself I was seeing it.)
The comet's present elongation from the sun has increased to 33 degrees, and it is currently located in western Gemini four degrees northeast of the star cluster M35 (and only 8 1/2 degrees northeast of Venus). Over the coming few weeks it tracks eastward across Gemini, and although its elongation is gradually increasing, and historically it is one of those comets that tends to be brightest after perihelion, the fact that that event took place seven weeks ago together with its receding from Earth suggests that it will probably fade from view before much longer. With our always "iffy" weather this time of year, and the full moon that comes next week, it is rather probable that this will be my only observation of it this time around.
The next return, in 2018 (perihelion early November) takes place under geometrical circumstances fairly similar to those in 1981, and it should be an easy object to observe then. I certainly hope that my personal circumstances in 2018 are much happier than they were in 1981, and while no one can predict the future, I believe there's a pretty good chance that they will be. We shall see . . .