COMETS 421 - 430
|421. COMET 110P/HARTLEY 3 Perihelion: 2008 February 3.49, q = 2.488 AU
I've mentioned in several previous entries that I fully expected the fall of 2007 to be a very busy time for comet observing, as indeed it has been. This is another comet that I had reasonable expectations of seeing, although it is also going to be among the very faint ones that I've been recently adding, and thus will probably be one that few "Countdown" participants will see. The comet was originally discovered in February 1988 by Malcolm Hartley in the course of a photographic survey program that was being conducted from Siding Spring Observatory in New South Wales, one of numerous comets (including several periodic ones) that he found while there. It has a current orbital period of 6.9 years and has been observed at every subsequent return; I successfully observed it, both visually and via CCD, at its previous return in 2001 (no. 283). Overall, including the various periodic comets (four of which I have now seen on multiple returns) Hartley's name now appears 13 times in my tally.
Prior to the previous return Comet 110P was imaged only seven months after passing aphelion, and thus it is legitimate to consider it as an "annual" comet, i.e., it is observable all the way around its orbit. As such it isn't "recovered" in the normal sense of that term. On the current return, the earliest observations of which I'm aware were made on August 18, 2006, by Krisztian Sarneczky at the Piszkesteto Station observatory of Szeged University in Hungary.
The geometry of this return is very good, with the comet's being at opposition around December 11, less than seven weeks prior to its perihelion passage in early February. Unfortunately, the comet seems to be somewhat fainter intrinsically than it was on the 2001 return; when I first picked it up on the evening of December 4 it was an extremely tiny and faint object near magnitude 14 1/2, about half a magnitude fainter than it should have been based upon the brightness I observed in 2000-01. Furthermore, it is currently traveling through the rich Milky Way star fields of central Auriga, and remains in this part of the sky for some time, although crossing into northeastern Taurus shortly before mid-January. It is probably about as bright as it is going to get, although it should remain near this brightness until perhaps the end of January; nevertheless, I probably will not be obtaining very many observations of it.
Here in the U.S. the holiday season is approaching, and the next couple of weeks are filled with holiday-related events at my son Tyler's school and elsewhere. This past weekend our family attended the banquet honoring the New Mexico State University Pride Band (of which my older son Zachary is a member), and meanwhile Tyler is now learning to drive and is perhaps giving his Dad a few additional gray hairs in the process. In addition to the comet observing I am diligently working on the Anousheh Ansari Matching Funds Campaign and, when I can, trying to prepare myself for the holiday season and life after that. I may or may not be adding any more comets to "Countdown" before the end of 2007, but in any event I feel there are going to be some interesting developments, both personally and with Earthrise, after the start of the new year.
This is a comet I fully expected to add to my tally at some point, but picking it up this early is a big surprise. The CCD magnitudes on some of the recent "Observations of Comets" Minor Planet Electronic Circulars (MPECs) published by the Minor Planet Center suggested it might be worth trying, and I decided to do so after reading reports of visual observations by a couple of experienced observers. My first attempt (when the comet was in a poor star field) was unsuccessful, but when I tried again on the evening of December 11 I clearly saw it as a very faint object of magnitude 14 1/2 that exhibited distinct motion over a two-hour interval. This is only the fifth comet that I have observed in excess of 18 months before perihelion passage; two of these are "returns" of the "annual" comet 29P/Schwassmann-Wachmann 1, one is the Centaur comet 174P/Echeclus (no. 384) that doesn't pass perihelion until 2015, and the other is Comet Hale-Bopp C/1995 O1 (no. 199).
The comet was discovered on November 18, 2006, by Eric Christensen during the course of the Catalina Sky Survey going on in Arizona; this is his 15th named comet discovery, out of a total of 19. (Christensen left the Survey earlier this year, and is now with the Gemini telescope program in Chile.) This is the second of his comets that I have seen; the other was his first one, the periodic object P/2003 K2 (no. 335), which is due again in early 2009 and which should hopefully be a "Countdown" comet around that time.
Christensen's comet is, intrinsically, a very bright one, but because of its large perihelion distance it unfortunately won't become a bright object in our skies. It has just passed opposition, and is currently located in northern circumpolar skies (declination +64 degrees) in the constellation Camelopardalis, a few degrees south of the star Alpha Camelopardali. It remains in this same general part of the sky for the next several months, probably brightening slightly by the time it goes through solar conjunction (38 degrees north of the sun) in mid-May 2008. The comet's orbit is steeply inclined and retrograde (inclination 127 degrees), and it travels even farther north after conjunction; when at opposition in early October 2008 it will be as far north as declination +76.5 degrees (in northern Cassiopeia) and perhaps as bright as 12th magnitude.
After that the comet begins heading southward, but will still be near declination +35 degrees when it goes through solar conjunction (44 degrees north of the sun) in late February 2009. Throughout the middle months of 2009 it should be an easy object for observation, being at opposition in early August and perhaps near 10th magnitude for several weeks on either side of that time. After another conjunction with the sun in January 2010 the comet is in opposition again in early July of that year; although it will then be near a declination of -46 degrees it may still be as bright as magnitude 12 or 13 and thus I may very well still be able to observe it.
It would appear that, barring anything unusual occurring, I will be following this comet for a very long time, very possibly at least 2 1/2 years and perhaps even as long as 1000 days. (Only four comets so far have made it that long, and two of these were "returns" of Comet 29P.) If only the comet could have had a smaller perihelion distance and have had a chance to become bright . . . Both the world and I should see some significant events take place by the time I'm done with Comet Christensen; at the very least, I should see my older son Zachary graduate from college and my younger son Tyler graduate from high school. The circle of life continues as the comets come, stay for a while, and then move on.
UPDATE: After its conjunction with the sun in early 2009 I picked up this comet in the morning sky during the latter part of March, at a relatively bright 10th magnitude (more or less consistent with the brightness it exhibited during the 2008 opposition). If this brightness trend holds up over the coming months it may be 9th magnitude, or perhaps even slightly brighter, around the time of opposition in August -- remarkably bright for a comet that is so distant. It is indeed unfortunate that such an intrinsically bright comet had to have such a large perihelion distance.
UPDATE: Following its conjunction with the sun in January 2010 Comet Christensen again emerged into the morning sky, initially visible only from the southern hemisphere during late February, but by mid-March I was also able to pick it up, low in my southeastern sky just before dawn. Its overall brightness is around 11th magnitude, consistent with its appearance from its 2009 opposition, and it should maintain something close to this brightness for the next few months as it approaches its next opposition. Over 27 months have now elapsed since I first picked up Comet Christensen, making it my 5th-longest comet (and 3rd-longest comet, if I exclude the "returns" of Comet 29P/Schwassmann-Wachmann 1) that I have ever followed.
A new year has now begun here on this planet Earth, at least as far as we humans measure time. (The whole scheme is, of course, rather arbitrary.) I have a deep intuitive feeling that there are some very fascinating developments in store for both Earthrise and for me personally during this new year of 2008, and I will share those developments on these pages as they take place. I will say at this time that I had an absolutely wonderful New Year's celebration, and I would like to extend my personal appreciation to those who made that possible.
Before the old year of 2007 ended, however, I was able to slip in one more comet to my tally (giving me a grand total of 31 comets observed during the year, my second-highest annual total ever). This is an object that was originally discovered in November 1990 by the team of Carolyn and Eugene Shoemaker and David Levy, during the course of a photographic survey program they conducted with the 46-cm (18 inch) Schmidt telescope at Palomar Observatory in California. The Shoemakers conducted this program from 1982 to 1994, during which time they discovered 32 comets (making Carolyn Shoemaker the all-time record holder for most comet discoveries by a woman), with David Levy joining this program in 1989. The Shoemakers and Levy collaborated for a total of 13 named comet discoveries, this one being the first of those and the first of nine periodic ones; the most famous of these, of course, is P/Shoemaker-Levy 9 1993e (no. 178), which collided with Jupiter in 1994. In addition to these 13 discoveries, David Levy is an accomplished amateur astronomer and visual comet discoverer (and good personal friend, too), and has visually discovered nine comets from his home near Tucson, Arizona. The appearance of this comet on my tally marks the 18th appearance of the name "Shoemaker" and the 16th appearance of the name "Levy," for second and third place, respectively.
I successfully observed this comet at its discovery return in 1990 (no. 147) as it reached a peak brightness of magnitude 12 1/2. Its orbital period was 17.3 years, although as a result of an approach to Jupiter in mid-2006 (0.62 AU) that has now been shortened to 16.4 years (still the third longest orbital period among comets which I've observed on two or more returns). It was recovered on this return by Rob McNaught with the Siding Spring survey in New South Wales on October 12, 2007, when fairly deep in southern skies. It has since come north and has brightened, and I first picked it up on the evening of December 28, when it appeared to be slightly fainter than magnitude 13 1/2.
The comet is currently an early evening-sky object, located in the southwest in the constellation Aquarius. It is traveling towards the northeast, and by the beginning of February will have crossed northwestern Cetus and have entered southern Pisces. Since it has already passed perihelion and is also receding from Earth it should theoretically be fading, however its brightness behavior in 1990 (when it wasn't discovered until almost two months after perihelion) and at this return suggests there could be some asymmetry in its brightness with respect to perihelion (as a few other periodic comets are known to exhibit). It is thus difficult to predict just what to expect in terms of the comet's future brightness, although my suspicion is that it is probably about as bright as it is going to get, and I'll probably only be getting a handful of observations of it before it fades away.
One curious little detail I've noticed is that this comet's perihelion passage was only 16 minutes before that of Comet 93P/Lovas 1 (no. 411). This is the closest pairing of perihelion times of any two comets within my lifetime tally. (The two objects were, of course, nowhere near each other in space at that, or any other, time).
One year ago we Earthlings were thrilling to the sight of Comet McNaught C/2006 P1 (no. 395) in our skies; when near perihelion in mid-January 2007 it was bright enough to be visible during the daytime, and then afterwards it became a spectacular and glorious sight as seen from the southern hemisphere during the latter half of that month. And now, a year later another Comet McNaught has been discovered, and although it won't become anywhere near as bright as its predecessor, if the initial orbits are correct it has the potential of becoming bright enough to at least see with binoculars, and possibly with the unaided eye. It won't be all that well placed, though, and as was the case for the earlier comet, the best views will be from the southern hemisphere.
The comet was discovered by Rob McNaught on January 10, 2008 during the course of the Siding Spring survey in New South Wales -- the first comet discovery of the new year. I happened to notice it as a relatively bright object on the Minor Planet Center's Near-Earth Object Confirmation Page, and went out that night and successfully observed it shortly after midnight (i.e., on the morning of January 11) as a faint and difficult object of 14th magnitude. The comet's discovery was announced later that same day, and I successfully observed it again the following night. This is Rob's 40th named comet discovery -- an absolutely incredible feat -- and this is the 14th comet of his that I have observed.
At discovery the comet was located in the constellation Puppis at a declination of -44 degrees (and thus difficult to view from my latitude), just half a degree southwest of the star Nu Puppis. It is traveling in a steeply inclined orbit (inclination 82 degrees, according to the most recent calculations at this writing) and had just passed opposition early this month. It is presently about as far south as it is going to get (for now), and over the next few months it will travel slowly north and west, crossing northeastern Pictor and then into Columba by the end of February. I'll probably lose it by sometime in April (by which time it might be 12th magnitude), but observers in the southern hemisphere should be able to keep following it, as it comes close to conjunction with the sun (although some 60 degrees south of it) during June and July; by the end of July the comet may be as bright as 8th or 9th magnitude.
After traveling to as far south as declination -46 degrees in mid-August, the comet again starts heading north, and makes its closest approach to Earth (1.29 AU) in early September. At that time it should be near its peak brightness (perhaps 6th or 7th magnitude) but still only visible from the southern hemisphere. It should finally become visible again from my latitude near the middle of October, when it will be 40 degrees from the sun in the evening sky and perhaps around 8th magnitude. The comet continues traveling north, being in conjunction with the sun (50 degrees north of it) in early January 2009 (when it may be near 11th magnitude), and it may still be 13th magnitude when it enters northern circumpolar skies near the beginning of April. Like several of the other recent comets, then, this one has the potential of my following it for over one year, although the orbit is still pretty preliminary at this time and some of the details could change.
Now that the holiday season break is over, things are kind of busy here around Earthrise. We have several funding proposals and other items due around now, and I may be heading up to Santa Fe for the New Mexico legislative session sometime within the next week or so. Here on the home front, this past weekend I watched my younger son Tyler participate in the New Mexico All-State music festival, and meanwhile my older son Zachary is about ready to celebrate his 21st birthday. (Hard to believe it's been that long already.) The possible forthcoming changes in my personal life that I've been hinting at in some of the recent comet descriptions are also underway to some extent, but I don't feel comfortable writing about them right now; by the time I'm finished following this comet, though, I imagine that whatever these changes might be will be in the process of coming to pass.
One little point of trivia: I've mentioned on my statistical page that January has been the most productive month for comet discoveries in my tally. This comet not only extends that record, but it also happens that the month of January has now produced at least one comet discovery or recovery for my tally every year going back to 1986; 2008 is thus the 23rd consecutive year for which this has happened.
UPDATE: More recent orbit calculations show that the scenario outlined above is generally correct, although the maximum southerly declination in mid-August is close to -47.5 degrees, the closest approach to Earth in early September is 1.32 AU, and the elongation from the sun when at conjunction in early January 2009 will be 46 degrees. I would say at this point that the comet will probably not become brighter than 7th magnitude.
UPDATE: According to reports I've read from the southern hemisphere, as of the latter part of August Comet McNaught had brightened to near magnitude 6 1/2, thus flirting with naked-eye visibility. If it continues this brightening trend it may reach a peak brightness of 6th magnitude or slightly brighter in early- to mid-September, and may still be somewhere between magnitude 6 1/2 and 7 when it becomes visible from the northern hemisphere the following month.
UPDATE: By the end of September Comet McNaught had again become observable from my latitude, very low in my southwestern sky during the early evening. The brightness seemed to me to be close to 7th magnitude, reasonably consistent with the fading trend that the southern hemisphere observers have been reporting recently. Over the coming few weeks the comet will climb higher into the evening sky and thus become somewhat easier to observe, but at the same time since it is now receding from both the sun and Earth it will likely continue fading. I expect to be able to follow it in binoculars for perhaps a month or so, and then telescopically for some time after that.
In mid-February 2007 I added the 400th comet to my tally (Comet 185P/Petriew P/2007 A3); now, just a little over 11 months later, I'm up to no. 425, already a quarter of the way through "Countdown." This ties the fastest I have ever added 25 comets to my tally, and is primarily due to the remarkable run of observable comets that appeared during the last few months of 2007. I stated in my introduction to "Countdown" that I estimated it would take between five and seven years to get to no. 500, and I still hold to that; there will certainly be "lean" periods during the months and years to come that will balance the recent heavy period.
This newest comet on my tally was discovered on January 23, 2007 by Brian Skiff in the course of the Lowell Observatory Near-Earth Object Search (LONEOS) program based in Flagstaff, Arizona. Although I don't know him extremely well, I have met Brian on a few occasions over the years; he has been based at Lowell Observatory since the mid-1970s and has a number of discoveries to his credit. This is the 15th named comet discovery for Brian (of 16 overall at this writing), and the 13th discovery of his via LONEOS (of 14 so far). This is the third named comet discovery of his that I have seen (and the first in eight years).
The comet is currently a morning sky object -- my only morning-sky comet at the current time, in fact -- and is located in Virgo four degrees southwest of the star Epsilon Virginis. It's a rather faint object of 14th magnitude, and after some unsuccessful attempts late last year and earlier this month I suspected it on the morning of January 18 and successfully confirmed that observation on the following morning, during the coldest night of the winter here so far, -2 degrees F., or -19 degrees C. (I realize that such temperatures may not be that big a deal to observers in some parts of the world, but it's still nevertheless a bit chilly.)
Comet Skiff will be reaching its stationary point in early February and will then begin its apparent retrograde motion. It remains within Virgo for the next several months, traveling gradually southward the entire time; it is at opposition in late March and should reach a peak brightness of 13th magnitude between March and July. I will probably lose it in the evening sky by about the end of July or early August, with observers in the southern hemisphere being able to follow it for perhaps another month or so. There is a possibility it might again be observable as a very faint object (14th magnitude) during the early months of 2009, but it will be pretty far south (declination about -45 degrees, and heading southward) so only observers in the southern hemisphere will be able to view it.
There's not much new since I added the previous comet to my tally. My younger son Tyler is participating in the Science Olympiad competition at Cloudcroft High School this weekend, and meanwhile I will definitely be heading up to Santa Fe early this next week for the New Mexico legislative session in hopes of getting some kind of funding for some Earthrise-related projects. Next weekend I'm part of the cast of a Cloudcroft Light Opera Company (CLOC) Murder Mystery performance, so I have some good food and fun times to look forward to . . .
38 years ago, on the evening of February 2, 1970, I observed a comet for the very first time in my life: Comet Tago-Sato-Kosaka 1969g. On that night it was a dim naked-eye object of 5th magnitude, located fairly close to the star Hamal (Alpha Arietis). Needless to say, a lot has transpired during the years that have passed since then, but as everyone knows I have continued to observe comets regularly. If weather and circumstances permit, and provided there are suitable comets in the sky at the time, I have always tried to make it a point to mark "anniversary night" by observing whatever comets might be around. This year's "anniversary" was quite notable, in that not only was there a dim naked-eye comet in the sky -- and not too far away from Hamal, either -- but, for the first time since that long-ago night, I added a comet to my tally on the evening of February 2.
Unlike the vast majority of recent comet discoveries (which are being made by the various comprehensive surveys that are operating), this comet was an accidental discovery by two Chinese amateur astronomers. It was first noticed by Tao Chen (of Suzhou in Jiangsu province) on a wide-field CCD image taken on February 1 by Xing Gao (of Urumqi in Xinjiang province) at the latter's Xingming Observatory on Mt. Nanshan during the course of a survey for new novae. They later identified images of the new comet on CCD images that had been taken on January 30 and 31, and Gao was able to obtain several images on February 2. At the time of its discovery the comet was in northern circumpolar skies (declination +62 degrees), in eastern Cepheus 2 1/2 degrees west-northwest of the star cluster M52 in adjacent Cassiopeia, and moving almost due eastward. The various images taken by Gao suggested that the comet might be brightening somewhat rapidly, and when I saw it on the evening of the 2nd it was right around 13th magnitude.
According to the preliminary orbit that is currently available, Comet Chen-Gao will remain in the northwestern evening sky, although it will soon begin moving more towards the southeast. During the rest of February it travels across Cassiopeia (including the western half of the "W") and enters Perseus by the beginning of March; it remains in that constellation throughout that month. Curiously, on March 26 it passes just a little over two degrees north of Comet 17P/Holmes (no. 414) -- although just how bright that object will be at that time is an open question. After this encounter the comet travels through eastern Taurus and northern Orion during April, and after the beginning of May will be entering Monoceros. I'll probably be losing the comet shortly after that time; observers in the southern hemisphere should be able to follow it for a while longer, until it fades away (perhaps by sometime in June).
The comet is nearest Earth (1.30 AU) in mid-March. If it brightens "normally" and I use my observation on February 2 as a baseline, then it should reach a peak brightness of about 12th magnitude during March and April. Since there was a suggestion that it might have been rapidly brightening when it was discovered, it's conceivable that the comet could become somewhat brighter than this around that time.
I've been in a somewhat "funky" frame of mind lately, as some of the changes in my personal life that I've been hinting at in some of my earlier comet descriptions are starting to take shape a bit, and there will probably be a lot more to come. I enjoyed the excellent Super Bowl football game this past Sunday (although I wish the Dallas Cowboys could have been playing in it), and on Tuesday (February 5) I was a site supervisor for one of the polling places of the "Super Tuesday" U.S. Presidential election caucuses. In all, though, it somewhat strikes me that the comet observation I made 38 years ago started me off on one of the major courses of my life, and the observations I made on the "anniversary" of that night are somehow signifying some of the new courses my life might take.
I suspect that many would-be "Countdown" participants are dismayed at the number of very faint comets that end up on this list -- such is, unfortunately, the way comet observing normally goes. At first glance, this is yet another hopelessly faint comet that many would-be observers would probably write off. But take heart: this one has the potential of becoming a fairly interesting and bright comet, possibly even reaching naked-eye brightness, later this year; the southern hemisphere will get the better end of the deal, but we northerners should also have something relatively decent to look at.
This comet was discovered on November 20, 2007, by Andrea Boattini during the course of the Mt. Lemmon survey in Arizona. Andrea is originally from Italy, and while in his native country developed a strong interest in near-Earth asteroids; during his research efforts there he discovered (or co-discovered) up to 170 asteroids (mostly main-belt objects). He has recently begun working with the Catalina and Mt. Lemmon program and has made several additional asteroid discoveries while there; one of these was the object 2007 WD5, which made some headlines when it made an extremely close approach to Mars at the end of January 2008. Comet C/2007 W1 is his first comet discovery, and I suspect there will be more of these to come.
Comet Boattini is traveling in a long-period orbit with an unusually small inclination of 10 degrees. It is currently a morning-sky object in south-central Virgo about nine degrees west of the star Spica, and when I first saw it on the morning of February 8 it appeared slightly fainter than 14th magnitude. It reaches its stationary point and begins apparent retrograde motion during the latter part of this month, and when at opposition in late March may have already reached 11th magnitude. As the comet moves over into the evening sky after that it should begin brightening more rapidly, and could be as bright as 6th magnitude when northern hemisphere observers like me lose it in evening twilight around the end of May.
Comet observers in the southern hemisphere will continue to have a pretty good view of Comet Boattini as it passes 0.21 AU from Earth on June 12, and three days later it will be at inferior conjunction, 41 degrees south of the sun; it may have reached 5th magnitude by that time, about its expected peak brightness (although one never knows). The comet then shoots over into the morning sky, and observers at my latitude should be able to pick it up again shortly after the beginning of July, when it will be in southern Taurus and perhaps still 6th or 7th magnitude. It travels more northward after that, and meanwhile begins fading as it pulls away from the sun and Earth; when at opposition in early October it may be no brighter than 12th magnitude. I'll probably lose it after about another month or so.
So, while there is no reason to think that Comet Boattini will become "Great," it does look like it could become a decent object, conveniently observable in the evening sky during the late (northern hemisphere's) spring. I encourage all "Countdown" participants to take advantage of this opportunity to view one of these fascinating wanderers from the outer depths of our solar system.
UPDATE: As of the beginning of March Comet Boattini had brightened to 13th magnitude, more or less as expected. Meanwhile, the most recent orbital calculations indicate that it is making its first visit into the inner solar system from the Oort Cloud. Such comets, of which Comet Kohoutek 1973f (no. 10) is perhaps the best-known example, have a tendency to be bright and active when far from the sun but then slow down their brightness development as they approach perihelion. This suggests, unfortunately, that the above scenario for Comet Boattini may be a bit optimistic -- although we won't know for sure until the comet actually arrives. The planetary perturbations that Comet Boattini experiences this time around will change its orbit enough so that it should return in approximately 63,000 years.
UPDATE: As I noted above, throughout the month of June 2008 when Comet Boattini was passing perihelion and was also nearest Earth, it was also going through conjunction with the sun and was visible only from the southern hemisphere. According to the reports from comet observers in the southern hemisphere it reached a peak brightness of about 5th magnitude (and thus dim naked-eye visibility) during this time. As of early July it has again become observable from my latitude, and appears to have faded slightly, being about magnitude 5 1/2 according to my observations. Although it will climb higher into the morning sky with each successive day, the fact that it is moving away from both the sun and Earth rather strongly suggests it will continue fading, although it should remain visible telescopically for a few more months.
Two weeks ago I "celebrated" my birthday -- marking half a century on this small planet we call "Earth." (I celebrated the occasion by hiking to an isolated but very beautiful spot in the southern Sacramento Mountains here in New Mexico that my father and I discovered back when I was 12.) It's hard for me to believe that I've been around this long already, and it's sobering to realize that, in all likelihood, my life is already more than half over. (Although I wouldn't mind hanging around long enough to see Comet 1P/Halley on its next return, at which time I would be 103 . . . )
To somewhat bring these thoughts home, shortly before I've written these words one of my heroes and inspirations, Arthur C. Clarke, passed away at the age of 90. I've been reading both Clarke's fiction and non-fiction since I was in junior high school, and in recent years I've had the pleasure of corresponding with him off and on. He personally gave me permission to use the title of one of his short story collections ("The Other Side of the Sky") as the name of the radio program that I hosted fairly recently.
The first comet that I've added to my tally since I hit "the big 5-0" is this object, which was discovered by the LINEAR program in New Mexico as far back as April 10, 2007. (This is the 178th comet that LINEAR has discovered, of 185 so far at this writing, and is the 49th comet I've observed with the name "LINEAR.") At its discovery this comet was a faint object over 18 months away from perihelion, and after reappearing in the morning sky earlier this year has now become bright enough for visual observations. After some unsuccessful attempts last month I suspected it on the morning of March 15 (after an extremely windy day the day before) and successfully confirmed it two mornings later as a very faint object slightly fainter than 14th magnitude.
At the present time Comet LINEAR is a morning-sky object in Serpens Cauda, located two degrees south of the star Eta Serpentis. It is traveling in an orbit almost exactly perpendicular to Earth's (inclination 88 degrees) and currently is moving almost due southward (although gradually turning towards the south-southwest); it is at opposition in early June, when it will be located in southwestern Ophiuchus and near a peak brightness of 12th magnitude -- a brightness it should maintain for several months. At the beginning of July it passes half a degree from the bright star Antares in the constellation Scorpius, and thereafter continues heading towards the south-southwest; I will probably lose it from my latitude sometime in September, when it will be in the constellation Lupus near a declination of -40 degrees.
The comet is in conjunction with the sun in late November, but will be some 37 degrees south of it at a declination of -58 degrees, and theoretically accessible to observers in the southern hemisphere. For the first few months of 2009 it remains in southern circumpolar skies, reaching declination -76 degrees in early February before beginning to head back north, and perhaps remaining near magnitude 12 1/2. Southern hemisphere observers may be able to follow it until perhaps June, by which time it will have traveled to near declination -40 degrees but will probably have faded to 14th magnitude. It will remain inaccessible from my latitude throughout this time.
As I indicated in an earlier entry, "G" was the only letter in the new comet designation scheme introduced in 1995 for which I had so far failed to observe a representative; this comet finally takes care of that (as I in fact predicted in that entry). It's a rather curious coincidence that the first comet I ever observed was a "g" comet in the old scheme, and that it then took me all this time before finally getting a "G" comet in the new one.
I say "hello!" to an old friend with this comet -- but it appears the visit is going to be quite brief, and I almost didn't get to say anything at all.
This comet's discovery is usually credited to an amateur astronomer in New Zealand, John Grigg, who first spotted it in late July 1902. Unfortunately, he was only able to follow it for less than two weeks, and apparently no one else saw it, and thus only a preliminary orbit could be computed for it. An amateur astronomer in South Africa, John F. Skjellerup, discovered a comet in May 1922, and astronomers soon realized that this was the same object that Grigg had seen two decades earlier. (Five years later Skjellerup, having returned to his native Australia, co-discovered the brilliant daylight Comet Skjellerup-Maristany 1927k). Back in the mid-1980s astronomer Lubor Kresak in then-Czechoslovakia determined that a comet that had been observed by the great French comet hunter Jean Louis Pons on two nights in February 1808 was also this same comet, during a close approach to Earth (0.12 AU).
Throughout most of the 20th Century Comet P/Grigg-Skjellerup had an orbital period close to exactly 5 years, although occasional close approaches to Jupiter have acted to increase its perihelion distance gradually, from 0.75 AU around the time of Grigg's discovery, to 0.9 AU when Skjellerup found it, to almost exactly 1.0 AU during the last third of the Century, to the present 1.1 AU. (The most recent approach, to 0.51 AU in 1999, also increased the orbital period to the present 5.31 years.) Although intrinsically a rather dim comet, many of the 20th Century returns have been quite favorable and have involved moderately close approaches to Earth, and thus it has often reached a peak brightness of 9th or 10th magnitude. During its 1992 return Comet Grigg-Skjellerup achieved some notoriety when the European Space Agency's Giotto spacecraft (which was one of those that had flown close to Comet 1P/Halley six years earlier) passed by the comet; although Giotto's camera had been damaged by its earlier encounter with P/Halley, other instruments were still functioning and were able to gather and return interesting data.
I saw Comet P/Grigg-Skjellerup on several returns early in my comet-observing days. My first return was in 1977 (no. 24), when it passed 0.18 AU from Earth in April of that year; as it was, this came during my freshman (or "plebe") year at the U.S. Naval Academy and I was only able to observe it once, when I was home for spring break. I saw it again on the subsequent return, in 1982 (no. 49), when it became only the second periodic comet (after 2P/Encke) that I observed on a second return. Finally, I saw it on its return in 1987 (no. 102); this was during the (northern hemisphere's) summer months, right after I had completed my first year of graduate school at New Mexico State University, and less than one month after I had purchased the Meade DS-16 telescope I do most of my observing with now. The returns since then have been significantly less favorable; I did look for it, although unsuccessfully, a few times during the "Giotto" return in 1992 (when it was poorly placed from the northern hemisphere but better observable from the southern), and I didn't bother looking for it during the unfavorable returns in 1997 and 2002 -- in fact, no observations of any kind were reported at this last one.
One single observation was reported when the comet was at aphelion following its 1987 return, and theoretically Comet P/Grigg-Skjellerup could be considered an "annual" comet. But because it was missed entirely at its 2002 return it is also fair to consider it a "recoverable" comet, and accordingly it was recovered on the current return by Luca Buzzi and Federica Luppi at the G.V. Schiaparelli Observatory in Italy on December 19, 2007. The geometry at this return is somewhat similar to that of the favorable return in 1977, but because the perihelion distance is larger now the comet doesn't come anywhere near as close to Earth (the closest approach being 0.56 AU around the time of perihelion in late March).
During many of its previous returns Comet P/Grigg-Skjellerup has exhibited a distinct asymmetry in its brightness behavior with respect to perihelion, i.e., it has tended to remain faint until just before perihelion passage, then it has brightened very rapidly and then gradually faded away. (A handful of other periodic comets also exhibit this same basic behavior.) Based upon the brightness it has exhibited at previous returns, I expected P/Grigg-Skjellerup to reach a peak brightness of perhaps 12th magnitude this time around. But apparently that didn't happen; after several unsuccessful attempts beginning in early March, I didn't see the comet until finally, on the morning of April 6, I picked it up as a very faint and vague object of 14th magnitude. (The rich Milky Way star fields that the comet has been traveling through certainly haven't helped in trying to observe it.) Perhaps the larger perihelion distance didn't bring the comet close enough to the sun to "trigger" the rapid brightening it has undergone in the past.
At present the comet is a morning-sky object located in southwestern Aquila, and it is moving moderately rapidly towards the northeast, remaining in Aquila throughout the rest of April. Unless there is some kind of "delayed" brightening, it will likely begin fading fairly rapidly within the near future, and I will probably only obtain a handful of observations of it. Indeed, I feel rather fortunate just to have been able to observe it at all.
Comets like this one have served to illustrate the passage of time in one's life. When I first observed P/Grigg-Skjellerup I was 19 years old and in my first year of (sort-of) "college;" during the most recent return in which I've observed it my older son Zachary was just a few months old; and as I observe it now Zachary is 21 years old and a college student himself. Because of the comet's increased perihelion distance and its non-integer orbital period, it will likely be a long time before I see this comet again; the next return during which visual observations are feasible probably won't be until that of 2029, when it again returns under conditions similar to this year's, and because of a slightly smaller perihelion distance (1.08 AU) may be slightly brighter. By that time I will be 71, Zachary will be 42 (and his brother Tyler will be 36) and I will most likely have grandkids -- and who knows what else might happen between now and then?
I have written in some of the recent entries about some changes in my personal life that are currently underway. Things are still very much in a state of flux right now, and probably will be for a few more months; until then, I don't really feel comfortable writing about them in this space. That being said, it is conceivable that my observations of this particular comet will be associated in my mind with some of these changes, and if that turns out to be the case I will write about it at the appropriate time.
This comet was discovered on the morning of May 2, 2008, by Andrea Boattini during the course of the Catalina Sky Survey in Arizona. This is Andrea's second comet discovery; his first was C/2007 W1 (no. 427), which at this writing is rapidly becoming a bright and interesting object in our evening skies. I successfully observed this newer Comet Boattini on the following morning, as a rather dim object of magnitude 13 1/2 which exhibited detectable motion over the course of a half hour or so.
Curiously, this comet's perihelion passage is only 4 1/2 days after that of the other Comet Boattini (according to the orbit available at this writing, which could be subject to change although probably not by much), but it will very probably not be a bright and interesting object like its namesake. It is presently located in eastern Delphinus about six degrees west of the globular star cluster M15 and, in an orbit inclined 60 degrees with respect to the ecliptic, is traveling towards the north-northeast, gradually turning more and more towards due north; it crosses into western Pegasus within a few days, then into Cygnus by the end of May and into Cepheus by the end of June. The comet is closest to Earth (1.50 AU) shortly after mid-June, and if it brightens normally it should reach a peak brightness of magnitude 12 1/2 throughout most of June and into July. Beginning in early August it passes north of declination +80 degrees where it will remain for the next three months (reaching a peak northerly declination of +84 degrees in early September) and it will probably fade from view sometime during that period.
I've written in earlier entries that I'm a member of our local acting troupe, the Cloudcroft Light Opera Company, or CLOC. During the summer we stage melodrama performances, and we are putting on such a play over the Memorial Day holiday weekend (three weeks from now) and again three weekends later. I'm in the cast of this particular play, in fact, I'm the villain! (a part I've always wanted to play in one of these things). We're in the midst of a fairly busy rehearsal schedule right now, and I've already attended a rehearsal today. Hopefully I'll have all my lines down by opening night . . .
UPDATE: The newest orbit calculations indicate a perihelion passage in mid-July (thus three weeks, not 4 1/2 days, after the brighter namesake comet). The overall scenario outlined above doesn't change drastically, although the northward climb is a bit faster. The comet is still closest to Earth (1.46 AU) shortly after mid-June and the peak brightness should still be magnitude 12 to 12 1/2 between early June and mid-July. It passes north of declination +80 degrees in late July and remains there until late November; in late October the comet passes within 20 arcminutes of the north celestial pole. As was true with the earlier scenario we will probably lose it sometime during this period.