COMETS 431 - 440
|431. COMET BESHORE P/2008 J2 Perihelion: 2008 March 20.85, q = 2.410 AU
Up until about a decade ago, a fairly large percentage of newly-discovered comets were already bright enough to be visually observable as soon as they were discovered -- in fact, many of these were visual discoveries. But, once the comprehensive surveys became operational (beginning with the LINEAR program in New Mexico, which went on-line in 1998) most comets, even those which eventually become bright, are discovered when they are far too faint for visual observations; in many cases, several months might elapse between the time a comet is discovered and the time it becomes bright enough to be detected visually. It is rather rare these days for a comet to be bright enough for visual observations at the time of its discovery, but that is precisely what happened with the previous comet; and now, in a rather unusual coincidence, a second such comet was discovered a few days later.
This newer comet was discovered on May 6, 2008, by Ed Beshore in the course of the Mt. Lemmon survey in Arizona. (This is his second comet, his first being a very faint object he found in late 2005.) I noticed it as a relatively bright object on the Minor Planet Center's Near-Earth Object Confirmation Page, and the next morning I successfully observed it as a small and relatively condensed comet of 14th magnitude. The discovery was formally announced several hours later. (Incidentally, this gave me my 20th observed comet in 2008, by far the earliest I have ever reached this total in any calendar year.)
According to the most recent calculation available at this writing, Comet Beshore is traveling in a relatively low-inclination direct orbit (17.6 degrees). It is currently an early-morning object located about three degrees northwest of the star Eta Ophiuchi, and is moving slowly westward; it will be at opposition near the beginning of June. As it moves over into the evening sky it should brighten a bit, and its motion begins to tend more southward; when it reaches its stationary point (and begins eastward motion) at the beginning of August it will be near a declination of -22 degrees (in the "head" of the constellation Scorpius) and may be near magnitude 11 1/2. The comet is nearest Earth (1.34 AU) in late July.
Comet Beshore spends most of the last few months of 2008 in the southwestern evening sky, traversing the rich Milky Way star fields in Scorpius and Sagittarius. It is at its most southerly declination (just north of -38 degrees) in late October, and when at perihelion will be located in southeastern Sagitttarius and probably near a peak brightness of 10th magnitude. It then moves more northward and (presumably) will begin fading, and may be around 11th magnitude at the beginning of 2009, when it will be located in southeastern Aquarius. It should remain visible for some time into the new year, but we'll probably lose it to both faintness and twilight by sometime in March.
Since the current orbit is still somewhat preliminary some of the above details could change (although probably not by much). While it probably won't become spectacular in any way, we at least should have a moderately bright comet to observe for the next several months.
UPDATE: The more recent orbit calculations present a rather different scenario from the one described above. Instead of being a long-period comet that is several months away from perihelion passage and that could become moderately bright, Comet Beshore turns out to be a short-period object (currently calculated orbital period 6.3 years) that was already past perihelion at the time of its discovery. It is still at opposition at the beginning of June, at which time it will also be nearest Earth (1.46 AU), but it probably won't be getting much brighter than it is now, and it will probably only be visually detectable until perhaps July.
This is under the assumption, of course, that the comet hasn't experienced some kind of outburst recently. Its current brightness suggests that its intrinsic brightness is relatively high -- unusually so for a previously-undiscovered short-period comet. The current orbit (still somewhat uncertain) suggests it should have last returned to perihelion in late 2001 or early 2002, and since the surveys like LINEAR were operating at that time it should have been discovered then if its current intrinsic brightness is "real." If, on the other hand, the comet is indeed in a state of outburst right now it may very well fade away within the not-too-distant future. Incidentally, regardless of the comet's true intrinsic brightness it is conceivable that once its orbit is better defined it might be found on some of the survey images from the previous return, and if that happens it would then be eligible for numbering (as what happened with Comet 191P/McNaught).
These types of changes in a comet's computed orbit do happen with newly-discovered comets from time to time. (One should keep in mind that this is not due to changes in the orbit itself, but rather is simply due to more data becoming available.) When the early data is limited and only covers a short arc (i.e., a few days), a variety of orbital solutions may fit that data equally well, and there isn't much of a way to separate the "true" orbit from the incorrect ones until more data is obtained over a longer arc. For newly-discovered comets the common procedure is to assume that the orbit is parabolic (i.e., long-period) until and unless the additional data demonstrates that it is a short-period object, as what happened here with Comet Beshore.
UPDATE: My speculation above that Comet Beshore might have experienced an outburst not too long before its discovery seems to have been correct. By the early part of June its brightness had dropped to about magnitude 14 1/2, instead of remaining near constant as it should have if its brightness trend had been more "normal."
The most recent orbital calculations (as of mid-June) indicate that Comet Beshore has an orbital period of almost exactly 6.5 years. The previous perihelion passage would have taken place in September 2001 and, although the viewing circumstances would not have been quite as favorable as this year's, it should nevertheless have been discovered then by the surveys operating at that time if it had been as bright as it was at the time of its discovery. The perihelion passage before that would have been in March 1995 and the viewing geometry almost identical to this year's, but with the exception of Spacewatch this was before any of the current surveys were operational.
Sometimes a close approach to Jupiter can trigger an outburst in a comet, but Comet Beshore hasn't made any such approaches for some time. It will approach 0.7 AU from Jupiter in 2024, which will increase its perihelion distance to 2.6 AU and its orbital period to 6.7 years.
It gives me great pleasure to add this particular comet to my tally. When I was preparing to get "Countdown" underway in early 2007 I put out requests on, among other places, the Yahoo! comets mailing list group, for experienced comet observers to act as mentors for the student participants of "Countdown;" among those who answered my call was Quanzhi Ye, a student at Sun Yat-sen University in Guangzhou, China, and who works with the Lulin Sky Survey that is conducted from Taiwan. Less than half a year later he came through in a big way, with his discovery of this comet.
Quanzhi discovered his comet on July 11, 2007, when it appeared as an essentially stellar object of 19th magnitude; because it wasn't immediately apparent on the discovery images that it was a comet (which had to wait for larger telescopes to determine) it was assigned the name "Lulin" as opposed to "Ye." Its unimpressive appearance at the time was likely due to the fact that it was then a year and a half away from perihelion passage, and was located relatively far from the sun and Earth (6.38 AU and 5.66 AU, respectively). The orbit is distinctly unusual in that its inclination is 178.4 degrees, i.e., it is almost exactly retrograde, being inclined only 1.6 degrees from the plane of Earth's orbit. Accordingly, it will remain close to the ecliptic throughout its visit to the inner solar system.
After being hidden behind the sun earlier this year Comet Lulin has recently appeared in the morning sky, and I successfully observed it on the morning of May 8, when it was located in eastern Capricornus and appeared as a small and moderately condensed object of 14th magnitude. Over the coming few months it will begin traveling westward through the zodiac constellations and (presumably) brightening; when at opposition in late July it will be located in eastern Sagittarius and possibly as bright at 11th magnitude. We should then be able to follow it in the evening sky until sometime in October, when it will be just east of the "head" of Scorpius and perhaps 10th magnitude.
Comet Lulin's main treat for us will come after the beginning of the new year, and in fact it should become visible in the morning sky in late December or early January, perhaps as bright as 8th magnitude. While still near the "head" of Scorpius at that time, it then begins a rapidly accelerating westward march through the zodiac constellations, being perhaps 7th magnitude when at perihelion. The comet is nearest Earth (0.41 AU) in late February and is near opposition shortly thereafter; at that time it could be a naked-eye object near 5th magnitude, and traveling northwestward through the constellation Leo at five degrees per day. It will probably begin fading quite rapidly thereafter, but may still be 12th magnitude when we lose it in evening twilight sometime in May. There is a slight possibility it might still be bright enough for visual observations when it emerges again into the morning sky near the end of August, but even if it is it probably won't remain visible for long.
So not only does a "Countdown" mentor discover a comet, it appears that this will likely become a bright and easily observable object. I hope that all participating "Countdown" students are able to obtain observations of this comet, and also take some inspiration from Quanzhi's discovery and recognize that they, too, might someday make discoveries of their own.
UPDATE: Almost exactly as I predicted above, I picked up Comet Lulin in the morning sky in late December 2008 at 8th magnitude. The scenario that I've described thus looks fairly likely, and it does indeed seem that we will have a naked-eye comet (although probably not an especially bright one) to enjoy in about two months.
Some of the comets that I've added to my tally over the years have been fairly easy objects to observe; others, meanwhile, have been more difficult. And then there are those . . . This comet definitely goes down as being among the most difficult I've seen, and it was through a fortuitous combination of good weather and sky conditions at the appropriate time, the skill I've acquired through observing comets over the many years I've been doing this, and sheer dogged determination, that I was ever able to pick this one up at all.
The comet was discovered on May 10, 2008 by Rob McNaught in the course of the Siding Spring survey in New South Wales -- his 42nd named comet discovery (extending his all-time record) and the 15th comet of his that I have seen. Even at the time of Rob's discovery it was clear that the comet was in the act of disintegrating, as on the discovery images it appeared as little more than a vague diffuse patch with very little in the way of what might be called a central condensation; the images I've seen that have been taken since then indicate that the comet has more or less maintained this appearance. I first tried for it on the morning of May 30, but didn't see anything convincing; the nearby bright crescent moon may have simply made the background sky too bright. The moon wasn't quite as bright the following morning, and I did suspect something then, although unfortunately I didn't get too good of a look at it before the dawn sky became too bright. I again had a suspect the following morning (June 1) but before I could be sure of my observation it moved into a rather crowded star field and I lost sight of it. Finally, on the morning of June 2 -- the first morning when there was no moonlight to affect things -- I successfully followed an extremely faint (13th magnitude) pale, ghostly object for over half an hour as it moved through the telescope's field of view, thus "bagging" the comet and verifying my suspected observations from the previous two mornings.
Compounding the difficulty in observing Comet McNaught is the fact that it is located very low in the northeastern sky just before dawn; its current elongation is 37 degrees, and this is shrinking as the comet approaches perihelion. It was nearest Earth (0.73 AU) just before the end of May, and it is racing towards the northeast at over three degrees per day. Presently Comet McNaught is located in eastern Andromeda, and it will enter Perseus on June 5, crossing the entire constellation and reaching a peak northern declination of +49 degrees on June 13 (at which time its elongation from the sun will be 28 degrees) before crossing into Auriga a day later. Assuming that the comet doesn't disintegrate completely it should remain visible for perhaps another week and a half from right now; by the time it reaches perihelion it will be almost in conjunction with the sun (23 degrees north of it), after which time it drops southward towards the far side of the sun as seen from Earth (passing just three degrees from the sun in mid-July) as whatever is left of it recedes from the inner solar system.
Things have been a bit quiet around here lately. At Earthrise we've been doing a little refocusing as some potential future projects are beginning to take shape; I hope to make some announcements to this effect by about the beginning of July. On the home front, my younger son Tyler is away at camp (as a counselor for a two-week stint at Band Camp), and meanwhile I've been receiving some rave reviews for my portrayal of the evil "bad guy" in the melodrama performances that our local acting troupe staged over the holiday weekend a week and a half ago. We have two more performances (on June 13 and 14) and I fully intend to keep perfecting my "bad guy" act!
Hot on the heels of my most recent comet, which is only visible low in the eastern sky before dawn, comes the newest addition to my tally, which is also only visible low in the eastern sky before dawn. According to reports I've read this particular comet has been visually detectable from the southern hemisphere since about the middle of May, and it has now moved far enough north to be accessible from my latitude, although it is still quite low in the pre-dawn sky and will remain so throughout the period of its visibility.
The comet was originally discovered in September 1886 by William H. Finlay, the First Assistant of the Royal Observatory at the Cape of Good Hope in South Africa. Since then its orbital period has varied between 6 1/2 and 7 years, and with a perihelion distance close to 1.0 AU it can occasionally have favorable returns, or very unfavorable returns depending upon what time of the year it arrives at perihelion. As it happens, P/Finlay's last reasonably good return came in 1960 (when it passed 0.42 AU from Earth); between the mid-1960s and the mid-1990s it was locked into a pattern wherein an orbital period of almost exactly 7.0 years continuously brought it to perihelion when it was on the far side of the sun as seen from Earth. A distant approach to Jupiter (0.96 AU) in September 1993 finally broke this pattern, and although the return in 2002 (perihelion in early February) was still pretty unfavorable, I was able to obtain a single observation of it at a low elevation (no. 304). A closer approach to Jupiter (0.28 AU) in May 2004 decreased the perihelion distance from 1.03 AU to 0.97 AU and shortened its orbital period to the present value of 6.50 years, and as a result is making it possible for the comet to be observed somewhat more easily than before.
On its current return P/Finlay was recovered on April 27, 2008 by the Italian astronomers Ernesto Guido and Giovanni Sostero (who have recovered quite a few expected periodic comets in recent years) utilizing a remote-controlled telescope in South Australia. When I first saw it on the morning of June 4 it was located in southeastern Pisces (at an elongation of 48 degrees) and appeared as a moderately condensed object near magnitude 11 1/2. Although this return is better than some of the recent ones it still isn't all that favorable, and its elongation will remain fairly small; as it travels north and east along the ecliptic (crossing into Aries in a few days, into Taurus near the end of June, and finally into Gemini in early August) the elongation shrinks to a minimum value of 41 1/2 degrees in mid-July before increasing again. (Because of the comet's northward motion it should gradually become easier to observe from the northern hemisphere as this is going on.) It may brighten slightly by the time it passes perihelion but will probably start to fade some after that; my guess is that it may remain visually detectable until perhaps sometime in early August.
The comet's next return (perihelion December 2014) is similar to this year's, except that it will be located in the evening sky; the return after that (perihelion July 2021) will be another morning-sky apparition that should be slightly better than this year's. Over time P/Finlay will finally begin to undergo some quite favorable returns, including that of 2034 (when it passes 0.18 AU from Earth in August of that year) and -- for those willing and able to hang around that long -- the return of 2060, when it passes 0.048 AU from Earth that October and should be a naked-eye object.
Unbelievably, I am now over one-third of the way through "Countdown." If I continue to add comets at the rate I have been since I launched the program, that would bring me to 500 by sometime in early 2011 -- much earlier than I had expected to reach that total. I still think my original estimate of five to seven years still holds, and although there are some expected short-period comets that I'll probably be adding within the not-too-distant future, unless there is an explosion of new discoveries I expect the rate of my adding comets will become more "normal" during the latter months of this year.
People who follow astronomy, and especially cometary astronomy, probably know most of the story: on the night of July 22-23, 1995, during a break from our normal summer monsoon season here in southern New Mexico, I was collecting observations of the two comets I was then following. After finishing with Comet 71P/Clark 1994t (no. 197) just before midnight, I saw that I had perhaps an hour to wait before my next target, Comet 6P/d'Arrest (no. 198) rose high enough above my house in order to be able to observe it easily; I was especially interested in observing this object, since it was my planned topic for the next edition of my weekly newspaper column "In Our Skies." While waiting for Comet P/d'Arrest to climb higher in the sky I decided to pass the time on that beautifully clear summer night by observing some deep-sky objects, but when I turned the telescope towards the globular star cluster M70 in Sagittarius I immediately saw that there was a dimmer, fuzzy "something" in the same field of view. That "something" turned out to be Comet Hale-Bopp C/1995 O1 (no. 199) and the rest, as they say, is history . . .
And now, exactly thirteen years later to the night, I again pick up comet 6P/d'Arrest on a new return. I didn't plan or contrive it this way; it's just that the monsoon season this year has been quite intense, and the night of July 22-23 was the first clear night we'd had here in about two weeks. I had tried for the comet on a couple of occasions in early July, but had not seen anything convincing, and after that it was simply a waiting game until the skies were again clear enough to make a further attempt. It's a fitting, almost eerie, coincidence that that finally occurred on the anniversary night of the Hale-Bopp discovery.
This comet was discovered as long ago as June 1851 by the Prussian astronomer Heinrich d'Arrest, who is best known for being Johann Galle's assistant on the night that that astronomer visually discovered Neptune as a result of a mathematical prediction by the French mathematician Urbain Le Verrier. Its orbital period has varied between 6.2 and 6.7 years (currently, 6.54 years), and it has been observed at most of its returns since then. During the early 1990s two independent teams of European astronomers determined that a dim naked-eye comet observed by the French astronomer Phillipe de La Hire in September 1678 was in fact P/d'Arrest during a close approach to Earth. Including that return, the current return is the 19th at which this comet has been observed.
During the 1930s Comet 6P/d'Arrest played an important role in our understanding of the phenomenon known as "non-gravitational forces" that act on comet nuclei. More recently, during its excellent return in 1976 (when it passed 0.15 AU from Earth and reached 5th magnitude) it became the first comet to have its rotation period measured by direct photometric (i.e., high-precision brightness) observations of its nucleus (as opposed to observing the evolution of jets in the coma, as had been done for earlier comets).
Following its 1995 return P/d'Arrest was observed in 1999 when only 3 1/2 months past aphelion, and thus it is appropriate to consider it an "annual" comet. The first observations at the current return were obtained on April 26, 2008 by Wesley Ryle and Larry Wasserman at the Anderson Mesa Station of the Lowell Observatory in Flagstaff, Arizona, and three days later by Joe Hobart at the private Kachina Observatory, also near Flagstaff.
Historically, 6P/d'Arrest has shown a brightness behavior that is strongly asymmetric with respect to its perihelion passage. Specifically, it tends to remain quite faint until shortly before perihelion, and then it brightens almost explosively, finally reaching a peak brightness some two to three weeks after perihelion. From that point it slowly fades away over the subsequent months, growing larger and more diffuse all the time. Not surprisingly, it seems to be doing just that this time around; when I saw it on the evening of July 22 it appeared as a small, condensed coma near magnitude 13 1/2 (despite being only 0.39 AU from Earth). I expect it to brighten rapidly over the coming weeks, becoming as bright as 8th magnitude, possibly even 7th magnitude, by late August and early September. (The geometry is, in fact, very similar to that of the 1976 return, but an approach to Jupiter (0.30 AU) in 1979 increased the comet's perihelion distance from 1.164 AU to near the present significantly larger value.) It should fade slowly from this peak brightness, perhaps remaining visually detectable until almost the end of this year.
The comet went through opposition in mid-July and is currently located in central Aquila seven degrees south of the bright star Altair. It remains an evening-sky object from now on, for the time being traveling towards the south-southeast and passing through Sagittarius, Capricornus, and Microscopium, until it reaches a peak southerly declination of -39 degrees in early October when it will be located in Grus. It then begins traveling towards the northeast, and will be in southwestern Cetus near the star Beta Ceti (or Diphda) at the end of 2008.
This is the fourth return at which I've observed 6P/d'Arrest. In addition to the return in 1995 I also saw it during the extremely favorable return in 1976 (no. 23) as well as at the subsequent return in 1982 (no. 51). In both 1976 and 1995 perihelion passage took place during the northern hemisphere's mid-to-late summer and under excellent geometry -- and, in what almost seems too eerie to me to be coincidental, both of these returns corresponded to changes in my personal life that essentially turned it upside down. In 1976 I had just graduated from high school and was getting ready to leave for the U.S. Naval Academy in Annapolis, Maryland; in fact, my first observation of P/d'Arrest on that return came only three days before my departure. Because of the "plebe summer" basic training I was undergoing at the Naval Academy I essentially missed that entire return; the only observations I was able to obtain were those I made on two consecutive nights just before I left New Mexico.
As I've already indicated, the 1995 return is closely connected to my discovery of Comet Hale-Bopp (which took place, incidentally, only four months after I had moved to my present residence here in Cloudcroft). It goes without saying that that particular event had an incredible impact upon my life.
The geometry at this return in 2008 is very similar to those in 1976 and 1995, and once again my life is set to undergo some very dramatic changes. I've been hinting at these in some of my earlier comet descriptions, and although I'm still not quite ready to announce them publicly, it now appears that these changes will be coming into fruition within the next two to three months. There is actually a fair amount of uncertainty as to exactly what lies ahead of me, although I can say that I fully expect to continue with my comet observing (and, of course, "Countdown") and in my efforts to fulfill the Earthrise vision. I will probably have to wait until I've added a couple of more comets to my tally before revealing what these changes are.
There are other events going on in my life, too. I indicated in an earlier entry that I was the "bad guy" in our local acting troupe's melodrama performances in late May and early June; we've just completed another set of melodrama performances, and I was once again the "bad guy" in this new play. (Am I being typecast?) My younger son Tyler was in this recent play as well, and he and I are both scheduled to be in the next melodrama performance that will be held the last weekend in August -- but I won't be the "bad guy" this time. Meanwhile, in a few days I am leaving for Devon Island in the Canadian Arctic to (hopefully, weather permitting) observe the total solar eclipse on August 1; I will be a guest of the Mars Institute, which runs a Mars simulation facility under contract to NASA on that site.
The next return of 6P/d'Arrest, in 2015 (perihelion early March), is very unfavorable and I will almost certainly not be able to observe it. The return after that, in 2021 (perihelion mid-September), is moderately favorable and in fact is almost identical to the return I observed in 1982; since my personal life was comparatively quiet at that time perhaps the same might be true in 2021. There is another "late summer" return in 2047, at which time I would be 89 years old; I'm not sure I even want to speculate about any "upheavals" my life might conceivably undergo at that time . . .
I was really hoping to add a comet to my tally on August 1 this year. As I indicated in the previous entry, I had plans to travel to Devon Island in the Canadian Arctic to try to observe the total solar eclipse that took place this morning from the Mars Institute's Mars simulation facility located there. Part of my reason for wishing to go there was to attempt observations of any comets that might be near the sun at the time of totality. In particular, the coronagraphs aboard the SOlar and Heliospheric Observatory (SOHO) spacecraft have detected over 1500 comets near the sun since SOHO's launch in late 1995; the large majority of these are members of the remarkable family of Kreutz sungrazing comets (which includes the Great Comet of 1882 and Comet Ikeya-Seki 1965f, both of which were easily visible in daylight when they appeared). It would have been a truly remarkable observation to have seen one of these Kreutz sungrazers, or any other SOHO comet for that matter, during the eclipse.
However, a few days ago I was called by the people who are on-site at Devon Island, who told me that the short-range weather forecasts were looking very unfavorable for eclipse day. After the forecasts did not improve after several hours we all came to the conclusion that it wasn't worth the expense and hassle for me to fly up to Devon Island just to be clouded out for the eclipse. (And indeed, I have recently been informed that the weather was cloudy with intermittent rain at the time of totality, so I would have been clouded out had I gone.) Meanwhile, a Kreutz sungrazing comet (C/2008 O1) was in fact discovered in SOHO coronagraph images yesterday, a rather dim object initially near 8th magnitude. Theoretically it would have been about seven hours away from perihelion, 2 1/2 degrees from the sun, and possibly 5th or 6th magnitude, during the time of totality on Devon Island, but the rather spotty data available suggests it probably had disintegrated by then -- at least, I have not read of any reports from people who might have seen it from those areas that had clear skies during totality. It appears, then, that I really didn't miss anything by not traveling to Devon.
But I did get at least part of my wish -- I added a comet to my tally on August 1. (And although this may appear to be a bit contrived, it isn't; it's just the way things worked out, as I've had to work around moonlight and the recent weather.) While nowhere near as dramatic as an eclipse Kreutz sungrazer, this comet is a reliable old friend, and was originally discovered in December 1904 by the French astronomer Alphonse Borrelly, who observed from Marseille Observatory and who discovered 11 comets between 1873 and 1912. Borrelly's comet has an orbital period of close to seven years (currently, 6.85 years) and the current return is the 14th at which it has been observed. At its previous return in 2001 it achieved some notoriety by having an encounter with the Deep Space 1 spacecraft, and the images returned back from Deep Space 1 revealed P/Borrelly's nucleus as an oblong, bowling pin-shaped object with several active jets.
Prior to its 2001 return P/Borrelly had been observed when near aphelion, and thus it can be considered as an "annual" comet. The earliest observations at the current return were obtained on August 19, 2007 by a team of astronomers led by Gian-Paolo Tozzi utilizing the 8.2-meter Antu Telescope (one of the units of the Very Large Telescope) at the European Southern Observatory's Cerro Paranal facility in Chile.
This is my fifth observed return of P/Borrelly, and it becomes the fifth comet that I have seen on five returns. I have previously observed it on its returns in 1981 (no. 43), 1987 (no. 107), 1994 (no. 190), and the "Deep Space 1" return in 2001 (no. 292). The 1987 and 1994 returns came under very favorable geometry and the comet reached a peak brightness of 7th and 8th magnitude, respectively; the other two returns were moderately favorable and it reached magnitude 10. I have both pleasant and unpleasant memories associated with some of its earlier returns: the 1981 return came when I first reported aboard ship during my Navy years -- a time that I consider among the darkest in my life -- whereas toward the end of its 1994 return it became the first comet that I observed from my present residence in Cloudcroft.
The present return is, by far, the least favorable one I have seen. When I saw it this morning it was very low in the eastern pre-dawn sky, being only 30 degrees from the sun and appearing at 12th magnitude. It is presently located in western Gemini and is traveling towards the east-northeast across that constellation, passing 1 1/2 degrees south of the star Pollux on August 20 and crossing into Cancer by the latter part of this month. Its gradually increasing elongation and northward motion will slowly help it become easier to observe from the northern hemisphere, but on the other hand the fact that it is already past perihelion will cause it to fade, by perhaps a full magnitude by mid-September. I will probably obtain at most only a handful of observations of it this time around.
The next return of 19P/Borrelly, in 2015 (perihelion in late May), is very unfavorable and I probably won't be able to see it. The return after that, in 2022 (perihelion in early February), is moderately favorable, similar to that in 1981 -- let's hope my life isn't quite as dark then. Meanwhile, within the relatively near future there are total solar eclipses occurring on July 22, 2009, July 11, 2010, and November 13, 2012, and these might perhaps give me opportunities to obtain observations of some eclipse comets. Finally, a paper published last year by JPL astronomers Zdenek Sekanina and Paul Chodas suggests that we could get another cluster of bright Kreutz sungrazing comets within the next one to two decades (on the nearer end of that, I'd like to hope). One way or another, then, perhaps someday within the not-too-distant future I'll finally be able to see one of these most remarkable of comets.
The late comet scientist Fred Whipple is reported to have remarked that "if you must bet, bet on a horse, not on a comet!" He was referring, of course, to the fact that comets are notoriously unpredictable when it comes to their brightness behavior. Statements such as this are usually brought up when comets fail to become as bright as they are initially expected, or hoped, to become, but sometimes the reverse is true: occasionally comets will outperform their expectations and become brighter than anyone had thought they might be. Then there are those cases where comets have unexpected outbursts and, for at least a little while, far outshine even the most optimistic predictions. A handful of comets on my tally (1% to 2%) are comets I never would have seen if it hadn't have been for these outbursts; a classic recent example is the huge outburst experienced by Comet 17P/Holmes (no. 414) late last year.
Another one of these unexpected comets has now joined my tally. This is an object originally discovered in May 1994 by the team of Carolyn and Eugene Shoemaker, the 32nd (and last) comet discovery they made during the course of the photographic survey program they conducted with the 46-cm (18 inch) Schmidt telescope at Palomar Observatory in California between 1982 and 1994. It was a distant and dim object that never got brighter than 16th or 17th magnitude, and it was found to be periodic with a current orbital period of 14.58 years. This is its first predicted return, and it was recovered on April 10, 2008 by the Catalina Sky Survey in Arizona; it wasn't recognized at the time, but was identified by Tim Spahr of the Minor Planet Center when he was examining Catalina data several days later.
As was the case in 1994 Comet P/Shoemaker 4 was expected to remain a distant and dim object this time around, and in fact it has remained around 18th magnitude ever since its recovery. However, on August 3 Gustavo Muler at the Nazaret Observatory in Spain noticed that the comet had undergone a large outburst to magnitude 14 1/2, and this was quickly confirmed by several other astronomers in Spain and elsewhere. After having to skip a night because of the summer monsoon conditions I had clear skies at the beginning of the evening on August 5, and I successfully spotted the comet as a tiny and condensed object slightly fainter than 14th magnitude. I was able to follow it as it moved through the star field for about 45 minutes before clouds moved in and eventually began raining.
Since we don't know how the comet will behave, it is not really possible to predict how much longer it might remain visually detectable. It already passed opposition back in early May and is now in the evening sky some 80 degrees from the sun, located in eastern Virgo near the star 109 Virginis. (Since the moon is now emerging into the evening sky observations of the comet will become quite difficult after another couple of days.) The comet is moving towards the southeast, and theoretically should remain accessible for about another month and a half before beginning to disappear into evening twilight. After being in conjunction with the sun in early December it begins to emerge into the morning sky by about February or March 2009, and is at opposition again in early August, when it will be located in the constellation Microscopium near a declination of -40 degrees; its predicted brightness then is about 1 1/2 magnitudes brighter than its current predicted brightness. My suspicion is that the outburst will subside over the coming days and weeks and that the comet will soon return to its "normal" brightness; with my having to contend with weather and moonlight in the near future it is entirely possible that my August 5 sighting will remain my only observation of it.
With the addition of 199P/Shoemaker 4 to my tally I have now achieved the milestone (mentioned in my statistics page) of having observed 100 numbered periodic comets. As of this writing there are 200 numbered periodic comets, so the percentage of these that I have observed is exactly 50%. Most of the periodic comets being discovered and numbered these days are very faint objects that are being detected by the comprehensive surveys, and although there are several periodic comets (including McNaught P/2007 H1 (no. 409) and Beshore P/2008 J2 (no. 431)) that I have seen on their discovery returns and that should eventually become numbered, I fully expect that my "observed" percentage of these objects will drop to well under 50% over the coming years.
UPDATE: By April 2009 Comet P/Shoemaker 4 had become accessible again in the morning sky, fairly low in the southeast before dawn. I've made a couple of attempts for it and haven't seen anything, which suggests that it has indeed faded back to its normal brightness following its outburst last August.
New short-period comets (with orbital periods of, say, 30 years or less) are routinely discovered all the time, especially in this era of the comprehensive surveys; as of this writing, seven such comets have already been discovered in 2008. A fairly large majority of these comets are eventually recovered at a future return and then become numbered. Those that aren't can become "lost" for a variety of reasons, most commonly because they weren't well enough observed to allow a good calculation of their orbits (this especially being true for comets discovered several decades ago) or because they were exhibiting an outburst at the time of their discovery and are in reality much fainter than the brightness at their discovery return would suggest. For a handful of comets an argument can be made that they have probably disintegrated since their discovery and thus no longer exist.
Many years ago I noticed that there were quite a few short-period comets discovered around the beginning of the 20th Century -- specifically, between the years 1880 and 1920 -- that hadn't been seen since their discovery returns. Over the years a handful of these long-"lost" comets have finally been seen again, either through intense recovery efforts or via accidental re-discoveries. I actually had a small hand in one of these stories: a comet discovered by Joel Metcalf in 1906 and "lost" afterwards was re-discovered by Howard Brewington in early 1991, and I successfully confirmed Howard's discovery just a couple of hours later (no. 150) -- curiously, from Kitt Peak National Observatory in Arizona where I was trying to obtain observations for my doctoral thesis. The comet, now known as 97P/Metcalf-Brewington, was quite obviously undergoing an outburst around the time Howard found it, and I suspect it was doing something similar at the time of Metcalf's discovery.
Another one of the turn-of-the-Century "lost" periodic comets was the first comet discovered by the French astronomer Michel Giacobini, who discovered 12 comets from Nice Observatory between 1896 and 1907. (Two of his discoveries, 21P/Giacobini-Zinner and 41P/Tuttle-Giacobini-Kresak, are periodic comets that I've seen on multiple returns; two of his others became moderately bright naked-eye objects.) He found this comet in September 1896 and it was followed for the next four months; there were several reports that it seemed to be accompanied by a small secondary nucleus, suggesting that it had split sometime earlier and was perhaps undergoing an outburst at the time. Calculations indicated an orbital period very close to 6 2/3 years.
On this past September 10 two Japanese amateur astronomers, Koichi Itagaki and Hiroshi Kaneda, discovered a 13th-magnitude comet in northwestern Aquarius on CCD images they had taken as part of a search for new novae. (Forty years ago Itagaki was one of several independent discoverers of Comet Tago-Honda-Yamamoto 1968a, but did not have has name given to that object; in recent years he and Kaneda have scored several successes in their nova search program, and Kaneda has discovered several main-belt asteroids.) Shortly thereafter German amateur astronomer Maik Meyer suggested that the new comet was identical to the long-lost Comet P/Giacobini, and calculations soon verified this identity; among other things, the current orbital period is 6.66 years and the comet has made 17 revolutions around the sun since 1896, and it appears that it passed only 0.51 AU from Earth in September 1962 but obviously wasn't detected then. In keeping with the IAU's official comet naming guidelines, the names of the two new discoverers were not added to the comet's name.
At the time the comet's discovery was announced we were receiving quite a bit of rain here in southern New Mexico as a result of moisture being thrown northward from what was left of Tropical Storm Lowell near Baja California; once that cleared out I had to wait out the bright harvest moon. I suspected the comet in fairly bright moonlight on the evening of September 16, and successfully confirmed that observation in somewhat darker skies the following evening, with the comet appearing slightly fainter than magnitude 12 1/2.
Comet P/Giacobini was at opposition in late July and passed 0.58 AU from Earth a month later, and is now visible throughout the evening hours. During the coming three months it tracks southeastward, then turning due eastward, across Aquarius (spending a couple of weeks in northern Capricornus around mid-October). It is entirely possible that the comet has recently undergone some type of outburst similar to what apparently happened in 1896, and thus it is difficult to predict just how long it may remain visible; in any event, since it is now past perihelion and is also receding from Earth it will probably only be bright enough for me to follow for perhaps another month or so.
The astute reader might note that, at the end of the previous entry, I commented that there were exactly 200 numbered periodic comets at that time (early August). Less than a month and a half later we are now already up to 205. There have been several first-time recoveries of recently-discovered periodic comets within the past two to three weeks; one of these, 204P/LINEAR-NEAT, is an object that I successfully observed at its discovery return in 2001-02 (no. 303) and may possibly see again late this year and/or early next year. Another one, 201P/LONEOS, is an object that I visually attempted unsuccessfully several times during its discovery return in 2001-02 but did manage to capture on CCD images on several occasions; it is poorly placed at the current return but is well placed at the next return in 2014-15 and I may see it then. The other two, 202P/Scotti and 203P/Korlevic, are very faint comets that I will probably never see.
Meanwhile, there are still six "lost" short-period comets from that 1880-1920 era . . .
UPDATE: My suspicion that Comet P/Giacobini might have had an outburst shortly before its re-discovery by Itagaki and Kaneda may be valid. By the latter part of September I was detecting a distinct fading in the comet's brightness; meanwhile, there have now been reports of at least two very faint companion comets accompanying the main comet. It seems entirely plausible that the splitting off of these objects produced a recent upsurge in brightness, very possibly a repeat of what apparently happened around the time of the comet's original discovery in 1896.
Incidentally, since the time I posted the original description of Comet P/Giacobini there has now been an eighth short-period comet discovered in 2008.
I've pointed out on my statistics page that the time that elapses between successive additions to my comet tally varies quite randomly. Although it's rare nowadays, sometimes I may go two or three months or more between successive additions, whereas there are other times when they come much quicker; on one occasion in December 1993 I added three comets to my tally in one night. The first time that I added two in one night came in October 1980, when the comets involved were 2P/Encke (no. 39) and 8P/Tuttle 1980h (no. 40); on the morning of September 28, 2008 I performed this feat for the 17th time.
The first of the two comets I added that morning is one of the several short-period comets discovered this year that I alluded to in the previous entry (a total that now stands at ten, incidentally). It was discovered via CCD imaging on August 27 by Michel Ory, a high school science teacher and amateur astronomer who observes from the Jura Observatory near Vicques, Switzerland; this is his first comet discovery, although since 2000 he has discovered 45 numbered asteroids and two supernovae. According to the most recent orbital calculations his comet has an orbital period of 5.84 years.
When I first saw the comet it appeared as an extremely faint object near magnitude 14 1/2, although because it is very small and condensed it was a little bit easier to see than that brightness would suggest. It is presently an early-morning object located in northeastern Cetus, and is traveling towards the northeast, crossing into Aries in mid-October where it will remain for the rest of 2008. The geometry of this return is quite favorable, as the comet is at opposition in early November only two weeks after perihelion passage, and in late October it will be nearest Earth (slightly under 0.40 AU). If its brightness behavior is "normal," it should brighten by perhaps a few tenths of a magnitude by the second half of October before fading, and remain visually detectable until perhaps mid- to late November.
Although the current calculations are still a bit preliminary it appears that the comet made a fairly close approach to Jupiter (between 0.25 and 0.30 AU) in November 2005. It's still a bit too early to tell just what the orbit was like prior to that, although calculations so far suggest that its perihelion distance and orbital period were somewhat larger than they are now; the geometrical circumstances at the previous return (sometime around mid-2002) would have been quite a bit less favorable than at the present return. It's also too early to predict what to expect at future returns, but since it will probably remain near the limit of my visual capability even under the current very favorable conditions, it would seem likely that this is the only return during which I will be able to observe it.
The second of the two comets I added to my tally on the morning of September 28, 2008 is this distant and rather nondescript object that was discovered by the LINEAR program in New Mexico on October 19, 2007. This is the 182nd comet discovered by LINEAR (of 188 so far as of this writing) and -- remarkably -- is the 50th comet I have observed that contains the name "LINEAR."
Following its discovery the comet was followed for the next 4 1/2 months before disappearing into twilight en route to conjunction with the sun. When it was recovered in the morning sky by the Mt. Lemmon survey in Arizona in late July it was unexpectedly bright, even making a brief appearance on the Minor Planet Center's Near-Earth Object Confirmation Page before being correctly identified. I've attempted it a couple of times since then unsuccessfully, but had no trouble seeing it on September 28 when it appeared as a very faint and small object slightly fainter than 14th magnitude.
The comet is presently an early-morning object in eastern Aries and -- traveling in a distinctly retrograde orbit (inclination 158 degrees) -- tracks almost directly westward across that constellation, passing one degree south of the bright star Hamal (Alpha Arietis) on October 18. It is at opposition, and also nearest Earth (2.42 AU), three days later, and crosses into Pisces four days after that, where it remains until crossing into Pegasus in early December (passing one degree south of the "Great Square" star Gamma Pegasi on December 7). The comet will probably not get much brighter than it is now (no more than a couple of tenths of a magnitude) and will probably fade beyond visual detectability by mid-November.
Readers may note that I've been pretty quiet concerning non-comet related items for the past several entries. In truth, there's not very much that I can write about right now; the personal life changes I've been alluding to for the past several months are still in the process of unfolding, and in the meantime I'm exploring some potentially exciting opportunities for Earthrise that could, conceivably, help it take a big step towards fulfilling its overall vision. This past weekend I spoke at the White Sands and Hale-Bopp Star Parties that were held here in the local area, and a few hours after my double-comet addition I attended a meeting of the New Mexico astronomical community wherein we discussed plans for the International Year of Astronomy coming up in 2009. (I made a brief mention of "Countdown" and pointed out that Comet Lulin C/2007 N3 -- presently running a bit brighter than expected -- should be a fairly bright object early in the year.) For those who are interested, all I can say at this point is "please be patient," as I will share the various developments at the appropriate times once they have taken place.