COMETS 401 - 410
|401. COMET LINEAR C/2006 XA1 Perihelion: 2007 July 21.90, q = 1.804 AU
I began my fifth "century" of comets by picking up this object on the evening of March 9, two days after I turned 49. Because of a slow-moving rainstorm (which brought needed moisture to our mountain environment) I wasn't able to confirm this observation until four nights later. (I had successfully imaged the comet a week earlier with the Earthrise Institute's CCD system, and I had reason to suspect it would be detectable visually.) I doubt if too many people will see this comet; it is an extremely faint and difficult object, even in the 41 cm telescope, and it probably won't get much brighter before we lose it in evening twilight.
The comet was discovered on December 9, 2006, by the LIncoln Near-Earth Asteroid Research (LINEAR) program that is run by MIT's Lincoln Laboratory and which utilizes two 1-meter GEODSS telescopes based at White Sands Missile Range in New Mexico. LINEAR was the first of the comprehensive sky surveys to become operational, going on-line in early 1998, and for the next few years it made an overwhelming number of discoveries of comets and near-Earth asteroids. Because of additional survey programs that have become operational within the recent past, LINEAR is perhaps not quite the dominant force it was earlier this decade, but it still contributes its share of discoveries. Overall, LINEAR has as of this writing discovered 177 comets (including three which were re-discoveries of long-lost periodic comets and which did not have the name "LINEAR" assigned to them); C/2006 XA1 was the 175th such discovery, and the 47th comet I have observed with the name "LINEAR."
As its "asteroidal" designation implies, C/2006 XA1 wasn't recognized as a comet at the time of its discovery, and in fact it was "lost" until it was re-discovered by LINEAR on January 8, 2007. At that time several observers reported it as being cometary. It is traveling in an almost-parabolic orbit with an approximate orbital period of 4000 years, that is inclined 30 degrees with respect to the ecliptic. At this writing it is in the northwestern evening sky in the constellation Perseus near the star Nu Persei, and about 14th magnitude; it is traveling to the east-southeast, and over the next two months it will traverse Perseus and Auriga (remaining in rich Milky Way fields) and perhaps may brighten by about one magnitude. After about mid-May its elongation will become too small for it to be accessible; at perihelion it is on the far side of the sun from Earth and will not be visible. After being in conjunction with the sun at the end of August it will emerge into the southern hemisphere's morning sky towards the end of this year, but will probably be too faint to be visually detectable.
This is one of the best-known comets, and the story of how the German mathematician Johann Encke identified comets observed in 1786, 1795, 1805, and 1818 as being the same object and successfully predicted its next return in 1822 can be found in almost any comprehensive book about comets. Since Encke's prediction it has been observed at every return except for that of 1944 (when it was very badly placed for observation, and the world's astronomers were preoccupied with World War II). The present return is the 60th at which it has been observed.
Comet 2P/Encke has the shortest orbital period (3.3 years) of any known comet. It has, for obvious reasons, been one of the most scientifically studied of comets, and much of what we know about comets has come from studies of this object. It was the first comet that was seen to exhibit the motions now described under the term "non-gravitational forces," and in part it was an attempt to account for these that Fred Whipple developed his "icy conglomerate" (more popularly known as the "dirty snowball") model for a comet's nucleus in the early 1950s -- a model which has since been completely verified. At its 1971 return 2P/Encke became the first short-period comet to be observed from space (by the Orbiting Geophysical Observatory 5 (OGO-5) spacecraft, which detected the large ultraviolet cloud of hydrogen now known to accompany almost all comets in the inner solar system), and at its 1980 return it became the first comet to be detected via radar, in experiments conducted by MIT student Paul Kamoun with the 300-meter Arecibo radio telescope in Puerto Rico. It was photographed when at aphelion in 1972, and has been an "annual" comet ever since.
This is my 10th observed return of 2P/Encke. I have observed it at its returns in 1971 (no. 4 -- my first periodic comet), 1974 (no. 12), 1980 (no. 39), 1984 (no. 65), 1990 (no. 145), 1994 (no. 181), 1997 (no. 231), 2000 (no. 280), and 2003 (no. 343). (In 1977 it was very badly placed for observation, and I wasn't in a position where I could have attempted it anyway; the 1987 return was primarily visible only from the southern hemisphere, although I nevertheless did try for it a couple of times). Throughout its various returns it has been around for some of the interesting times in my life: when I first saw it in late 1970 I was 12 years old, entering adolescence and starting to discover girls; in 1980 I was in the U.S. Navy and stationed in southern California, and it was one of the first comets I showed my then-girlfriend now-wife Eva (who was a bit underwhelmed); in 1984 I had just started working at JPL and was observing regularly with Charles Morris (owner of the Comet Observation Home Page); in 1990 I was a graduate student at New Mexico State University and working hard on finishing my doctoral thesis; in 1997 I observed it from Australia while in that country to observe Comet Hale-Bopp and give a series of public talks; and in 2000 I had just returned home from my second trip to Iran.
For the northern hemisphere, the present return of 2P/Encke is rather unfavorable. When I first picked it up on the evening of March 13 (after some earlier unsuccessful attempts) it was in western Pisces, low in the evening sky only 27 degrees from the sun, and appeared as a dim diffuse object only slightly brighter than 12th magnitude. It is traveling towards the east-northeast (entering Aries by the end of March) and remains at a small elongation. Since it is brightening as it approaches perihelion it may remain accessible through the first couple of weeks of April, although its elongation will drop below 20 degrees after the 16th (by which time it might be 7th or 8th magnitude). After passing perihelion it will spend a few days in the field of view of the LASCO C3 coronagraph aboard SOHO at the end of April, and then it emerges into the southern hemisphere's morning sky in early May. The view from the southern hemisphere should be relatively good, as the comet passes 0.51 AU from Earth in mid-May, although it will probably fade beyond visual range not too long thereafter.
The 2010 return of 2P/Encke (perihelion passage in early August) is extremely unfavorable, being similar to those of 1944 and 1977, and it is quite questionable that I'll be able to observe it (although I will probably at least attempt it). The return after that, in 2013 (perihelion in late November) is, on the other hand, very favorable for the northern hemisphere, and it should be an easy object to observe then. By that time it is distinctly possible that I will have achieved comet no. 500.
UPDATE: On April 20 Comet 2P/Encke encountered a massive coronal mass ejection event from the sun, which (temporarily) completely ripped its tail away. An October 1, 2007 NASA press release describes this event in detail, and displays it in a dramatic movie utilizing images taken with the Heliospheric Imager instrument aboard the STEREO spacecraft.
UPDATE: Perihelion passage during the 2010 return of P/Encke was on August 6, and as I indicated above this return was very unfavorable, at least for the northern hemisphere. The maximum elongation from the sun, 25.4 degrees, took place in mid-June when the comet was too faint to attempt, and while there was a brief "window" in late June and early July when it might have theoretically been detectable, moonlight and the summer monsoon in these parts conspired to keep me from attempting it during that time. This thus becomes the third return of P/Encke that I have failed to observe during the four decades that I have been following comets.
After spending a few days in early August in the field of view of the LASCO C3 coronagraph aboard SOHO P/Encke began emerging into the southern hemisphere's evening sky shortly after the middle of that month as an object around 8th or 9th magnitude. Historically this comet tends to fade and diffuse out fairly rapidly after perihelion, and since it remains on the far side of the sun from Earth (the closest approach to Earth being a relatively distant 1.11 AU at the end of August) it will probably remain visible for at most two to three weeks. During this time it travels from southeastern Leo into Virgo and across the southern regions of that constellation, passing 15 arcminutes south of the "Sombrero Galaxy" M104 on August 30.
As I also indicated above, I now have the very favorable return of 2013 to look forward to -- and, barring anything very unusual happening, I should be well past comet no. 500 by then.
When I celebrated my birthday ten days ago my comet tally was at 400, and I had only added one comet to that list over the previous 4 1/2 months. Now, in just ten days I've added three more -- which just goes to show that the appearances of comets in our sky can be rather random.
It's St. Patrick's Day, and springtime is coming to the New Mexico mountains. My older son Zachary (a sophomore in college) is on spring break this week, and will be spending a few days home with us later in the week. Meanwhile, I'm getting ready to attend a concert by the rock band Evanescence in a couple of days.
This comet was discovered on March 13, 2007, by Gordon Garradd, who works with the Siding Spring survey based in New South Wales. This program went on-line in 2004 and is the only comprehensive survey in the southern hemisphere. It has found a fairly large number of comets and near-Earth asteroids since then, probably the most dramatic of which was Comet McNaught C/2006 P1 (no. 395) which became a daylight comet earlier this year. This is Gordon's fourth named comet that he has found while working with the survey, and the second of his I have seen (the other being C/2006 L1 (no. 398)). I consider Gordon a personal friend, and have observed with him both at his residence in Loomberah, New South Wales and at my residence in Cloudcroft, New Mexico. He provided me with some very helpful advice as I was beginning to get my imaging program underway.
When I observed Comet Garradd this morning it was a dim and diffuse object only slightly brighter than 14th magnitude. It is presently located near the star Sigma Librae, and is moving to the west-northwest in an orbit that is almost exactly retrograde to Earth's. Consequently it is rapidly approaching both opposition and our planet, and will be at opposition at the end of this month before passing 0.49 AU from Earth in early April. It should be near its brightest at that point which, based upon my observation this morning, should be somewhere around 12th magnitude. It then moves over into the evening sky, and although still approaching perihelion it will likely fade rapidly as it recedes from Earth. By the latter part of May it will probably have faded beyond visual range, and will also be entering evening twilight.
After observing Comet Garradd this morning I also grabbed my first observation of the new Nova Cygni 2007, which is currently about 8th magnitude. This object was discovered on March 15, 2007 by Japanese amateur astronomer Akihiko Tago, who was one of the discoverers of Comet Tago-Sato-Kosaka 1969g, my very first comet. He had discovered another comet the previous year, and since then has discovered several novae as well as one additional comet, Comet Nishikawa-Takamizawa-Tago 1987c (no. 98). That particular comet was discovered three days after Zachary's birth, and was the first comet I added to my tally after that rather momentous occasion in my life. I am happy to see that Akihiko is still active and making discoveries after all these years.
UPDATE: Comet Garradd appears to be in an intermediate-period orbit of a few centuries; the most recent calculations indicate an approximate orbital period of 525 years. It has also brightened dramatically as it has approached perihelion (a behavior not unprecedented in intermediate-period comets); in early April, when nearest Earth, many observers were reporting it as being between 9th and 10th magnitude. Theoretically, this is about as bright as it will get, but it is conceivable that it may continue to brighten further as it approaches the sun.
With all the comprehensive surveys that are operating these days, it is quite rare now for a comet discovery to be made by an amateur astronomer -- but that is precisely what happened with this comet. The discovery was made on March 15, 2007 by Terry Lovejoy, an amateur astronomer residing in Thornlands, Queensland. Terry has been an active visual comet observer for over 20 years and has made a number of important and interesting observations. I had the pleasure of meeting him ten years ago when I was in Brisbane to give a public talk.
This turns out to be the first comet ever to be discovered with a digital SLR camera. Terry began searching for comets via this method in 2004, and had a couple of near-misses before making this discovery. He writes that the discovery took place on only the second morning he had searched for comets during 2007; his discovery images are posted here.
When discovered Comet Lovejoy was about 10th magnitude, located in the morning sky in the constellation Indus (southeast of Sagittarius), and visible only from the southern hemisphere. It is traveling in an orbit that is almost perpendicular to Earth's, and thus is moving almost due north; it has now become visible from the northern hemisphere as well. When I picked it up on the mornings of April 9 and 10 it was in eastern Sagittarius and was about 9th magnitude, although somewhat more difficult to see than that would suggest due to the nearby bright moon. Although now past perihelion it is still approaching Earth, and comes to within 0.44 AU of our planet in late April; by that time it will have crossed the constellation of Aquila and have entered Hercules, and should be perhaps half a magnitude or so brighter than it is now. The comet continues its northward trek after that, and by mid-May enters northern circumpolar skies; it will probably be fading by then but should remain visually detectable until perhaps July.
UPDATE: On May 26, 2007, Terry Lovejoy discovered his second comet, C/2007 K5, only a little over two months after his first discovery, and again with a digital SLR camera. The new comet was in the constellation Lepus in the evening sky approximately 45 degrees southeast of the sun, and was near 13th magnitude. This is the first incidence in over 11 years of an amateur astronomer's discovering two comets in such a short period of time, and is an especially remarkable feat in this era of comprehensive sky surveys. According to his account this discovery came about after only 20 hours of searching since his earlier discovery.
Unfortunately, it does not appear I will be able to observe this new Comet Lovejoy. According to the most recent orbital calculations it had already passed perihelion in early May and is receding from both the sun and the earth; it will remain at a small elongation from the sun in a region of the evening sky that is inaccessible from my latitude. You win some, you lose some . . .
UPDATE: Even from the southern hemisphere, Comet C/2007 K5 remained an elusive object, and very few visual observations were made. Meanwhile, orbital calculations have now revealed that the comet is traveling in an intermediate-period orbit, with the most recent calculations indicating an approximate orbital period of 345 years.
By any standard, this object is one of the most interesting and unusual periodic comets that we know about. It was originally discovered on May 12, 1986 by California amateur astronomer (and personal friend) Don Machholz; together with Charles Morris, I had the privilege of officially confirming his discovery the following morning (no. 93 -- incidentally, the last comet I would add to my tally before leaving California and moving back to New Mexico). Its unusually small perihelion distance made it an interesting comet almost right away, but the determination that it was in a short-period orbit (period only 5 1/4 years) was what really called attention to it. It has the smallest perihelion distance of any known periodic comet.
The comet's orbit is unusually highly inclined for a short-period comet (60 degrees) and has apparently been stable for several millennia. Its perihelion distance is gradually shrinking and, if the comet survives, the orbit will almost become "sungrazing" within a few centuries. There has been much speculation that P/Machholz 1 may be related to some other interesting inner solar system phenomena, including some meteor streams (such as the prominent Quadrantid shower along with some weaker and lesser-known showers) as well as the Marsden and Kracht comet groups that have been identified in SOHO LASCO coronagraph data during the past several years.
This is the fourth return I have seen of P/Machholz 1; in addition to the discovery return I also observed it in 1991 (no. 161) and 2002 (no. 300). The 1996 return was very unfavorable, and while the 2002 return (during which it put on a spectacular show in the SOHO LASCO coronagraphs) was also quite unfavorable, I managed to see it twice when at a small elongation. Meanwhile, this was the third comet discovery for Don, a pursuit he began in 1975. To date he has discovered ten comets (his most recent being C/2004 Q2 (no. 355), which became a bright naked-eye object for a few months in late 2004 and early 2005); I have observed all ten of these, and with the various returns of this comet as well as his other periodic comet (141P/Machholz 2) his name now appears 15 times in my tally, which ties him for third place.
P/Machholz 1 was observed around aphelion following its discovery return, and thus is considered an "annual" comet. To my knowledge, there were no observations obtained around the most recent aphelion, and the earliest observations of the current return of which I'm aware came when it appeared in SOHO SWAN images beginning March 13, 2007. Around the time of perihelion it was easily visible in LASCO C3 images from SOHO, and was a rather spectacular object in the HI1A SECCHI images obtained from the STEREO spacecraft. The first ground-based observations were obtained around April 9, when it was perhaps 7th magnitude. Because of some poor weather (including a mid-April snowstorm!) my first observations were somewhat delayed; it appeared at about 8th magnitude when I finally saw it on Saturday morning, April 14.
Over the coming few weeks the comet's placement in the morning sky grows substantially better, and between now and the end of April it crosses almost due westward across the "Great Square" of Pegasus. (On the morning of April 27 it passes just north of the star 51 Pegasi, the first sun-like star around which a planet was discovered, in 1995.) Historically the comet has tended to fade fairly rapidly as it recedes from perihelion, and thus will probably be around 11th magnitude near the end of April and will be near the end of visual detectability by about mid-May.
The comet's next return in 2012 (perihelion in mid-July) is moderately favorable (being quite similar to that in 1991) and thus it will probably show up again in my tally between now and comet no. 500. The two subsequent returns, in 2017 (perihelion late October) and 2023 (perihelion late January) are relatively unfavorable, but during the return after that, in 2028 (perihelion mid-May), the comet passes just over 0.3 AU from Earth after perihelion and should be easily visible from the northern hemisphere.
I am a member of our local theatrical troupe (the Cloudcroft Light Opera Company, or CLOC) and this weekend I am part of the cast that's staging a Murder Mystery production at The Lodge in Cloudcroft. On another personal note, my younger son Tyler (currently away in San Antonio, Texas on a high school band trip) just celebrated his 15th birthday a few days ago. For a point of reference, at the time of my 15th birthday my comet tally stood at 8, and although I couldn't have known it at the time, Comet Kohoutek 1973f (no. 10) was discovered on that very day. While it didn't quite become the "Great Comet" that many of us might have hoped for and expected, I still rank Comet Kohoutek among the best ten comets that I've ever observed.
UPDATE: As interesting and unusual as this comet is, observations obtained during this return suggest it might even be more unusual than previously thought. A photometric study by David Schleicher at the Lowell Observatory in Arizona indicates that it has a very unusual chemical composition, possibly suggesting that it might have come from interstellar space (i.e., originally from another solar system). This scenario is discussed quite extensively in a recent press release from Lowell, although it should be kept in mind that other explanations for the comet's unusual composition exist (discussed in this recent article).
As I mentioned above, P/Machholz 1's next return in 2012 is moderately favorable, and we can be sure it will be extensively studied then!
Once again the LINEAR program in New Mexico makes an appearance on my "observed comets" list. This is the 48th comet I have observed which contains the name "LINEAR" -- by far, the most of any discovering entity. My first "Comet LINEAR" was C/1998 K2 (no. 243) -- LINEAR's second comet discovery -- which I added in late May 1998, just a couple of months after LINEAR went fully on-line. While many of the LINEAR comets have been rather faint objects, I've observed three of them with my unaided eye: C/2001 A2 (no. 290), C/2000 WM1 (no. 295), and C/2002 T7 (no. 338).
This particular Comet LINEAR was discovered on November 13, 2006. It was not immediately apparent that it was a comet, however its orbit (which is retrograde) was highly suggestive of its being cometary, and in early December Carl Hergenrother, utilizing the University of Arizona's Kuiper reflector on Mount Bigelow, obtained images that showed that it is indeed a comet. After being in conjunction with the sun earlier this year it emerged into our morning sky towards the end of March, and I made my first (unsuccessful) attempts for it during mid-April. Following the recent full moon I began making new attempts this past weekend, although due to a significant amount of recent rain -- what could almost be considered an early monsoon season -- the sky conditions here haven't been very good. On Saturday morning, May 12 -- right after I had observed Comet 96P/Machholz 1 (no. 405) on the 21st anniversary of its discovery -- I suspected "something" in Comet LINEAR's location. Under somewhat better conditions the following morning my suspicions were strengthened, and on Monday morning, May 14, under good sky conditions I was able to confirm the observations of the previous two mornings. The comet currently is a rather faint object near magnitude 13 1/2.
For the time being this Comet LINEAR is strictly a northern hemisphere object. It is currently located north of the "Great Square" of Pegasus, and is moving almost directly northward. It turns toward the northwest by the middle of June, and crosses the constellations of Lacerta and Cepheus before entering Draco. It reaches its maximum northerly declination of +69.5 degrees in early July, at which time it is also near opposition; based upon its current brightness it may be as bright as 9th magnitude then. The comet then starts heading southwestward and makes a rapid descent into the evening sky, passing 0.58 AU from Earth in mid-July when it may be near a peak brightness of magnitude 8. By the end of July it becomes primarily a southern hemisphere object, and may still be as bright as 11th magnitude when it disappears into evening twilight around mid-September.
For a completely meaningless bit of trivia, this is the first comet I've seen that contains the letter "Z" as part of its discovery designation. In the old designation scheme that was utilized prior to 1995 (whereby the first comet discovered or recovered in a given year was assigned the letter "a," the second "b," and so on) four years made it as far as "z"; I attempted three of these comets, all unsuccessfully. In the new scheme that was introduced at the beginning of 1995 (where the initial letters refer to half-months of the year), there is no room for "Z," since "Y" indicates the second half of December. The only way a comet can now contain "Z" within its designation is if the "Z" is the second letter of an originally assigned asteroidal designation, as is the case with this comet. This is the fourth discovered comet which contains a "Z" in this manner, but the first three were very faint objects that I didn't attempt.
It turns out that "z" was the only letter I failed to observe in pre-1995 comets. The only (initial) letter I have failed to observe so far in the post-1994 scheme is "G" (i.e., discovery in first half of April), although I have attempted several such comets and have even imaged two via CCD. (I did observe one pre-1995 "G" comet that was retroactively assigned such a designation after the new scheme was implemented, and have observed one post-1994 comet where "G" was the second letter of an asteroidal designation.) This dearth of "G" comets shouldn't last forever, and in fact there's a reasonable chance that Comet C/2007 G1 -- another LINEAR discovery -- will become visually detectable by about this time next year.
This was almost "the comet that got away." Fortunately, I had good weather at the right time, and was able to grab a glimpse of this apparently small and/or weakly active comet, and it will probably end up as a "one-time wonder."
As was the case with two of the above comets, and as its "asteroidal" designation indicates, this object wasn't recognized as a comet at discovery. That event took place on November 20, 2006, and the discovery was made by Alex Gibbs with the Mt. Lemmon survey going on in Arizona. (The Mt. Lemmon survey has been operational since late 2004 and is an arm of the Catalina Sky Survey going on in the same state.) Although its initial appearance was completely asteroidal, its orbit (retrograde, with a small perihelion distance) made it a prime candidate for being a possible comet. Numerous observations up through the end of 2006 revealed no cometary activity, however, although observations obtained at Mauna Kea Observatory in Hawaii in late December suggested that its image was slightly larger than that of stars.
Following that, there were no further reported observations for several months, although I did unsuccessfully look for it both visually and via CCD in mid-February before it entered solar conjunction. It emerged into the southern hemisphere's morning sky near the end of April, and at that time two Italian astronomers, Ernesto Guido and Giovanni Sostero, utilized a remote-controlled telescope in Queensland which revealed that the object was accompanied by a faint coma with a total brightness of about 14th magnitude. Its stay in the morning sky was brief, and shortly after mid-May it went through inferior conjunction, passing 0.26 AU from Earth on May 21.
The comet has now emerged into the evening sky, and is rapidly climbing higher in the sky each night as it recedes from Earth. I managed to spot it on Wednesday evening, May 23, when it appeared as a very faint and "soft" object of 13th magnitude, that traveled across the entire telescope field of view during the half-hour that I watched it. It will probably fade quite rapidly and be beyond the range of visual observability within a few days; meanwhile, the bright moon (already at its first-quarter phase at the time of my observation) will make any observation attempts even more difficult.
Part of the reason that I probably won't see this comet again is that I am leaving tomorrow for the International Space Development Conference in Dallas, Texas, where among other things I will be speaking. By the time I return next week the nearly full moon will preclude any visual observations (although it's possible I might be able to image the comet with CCD). Then, by the time we have a dark evening sky again, the comet will almost certainly be too faint to be detected visually. While I try to avoid having "one-observation" comets whenever possible, in some cases there's not much that can be done about it, and I'm actually quite fortunate that I was able to obtain an observation of this particular comet during its very brief visit to our skies.
As much as I enjoy observing bright comets, it turns out that a significant fraction of the comets that I do end up observing are very dim objects that are difficult to detect. Such is the case with this distant comet; I suspected it at 14th magnitude on the morning of June 8, but poor weather (our continuing early monsoon season here in New Mexico), travel (I spoke at the North American Jules Verne Society conference in Albuquerque over the weekend), and the fact that the comet has been in some very poor star fields, prevented me from confirming this observation for almost a week. Finally, on the night of June 13-14 I was able to detect the comet both visually and via CCD imaging, thus verifying my earlier sighting.
This comet was discovered as long ago as June 3, 2005 -- over 2 1/2 years before perihelion passage -- by Rob McNaught in the course of the Siding Spring survey based in New South Wales. Rob has been a very active astronomer for well over two decades, and I consider him to be one of the top observing astronomers in the world. Prior to the current Siding Spring survey he worked with an earlier survey program at Siding Spring that was piggy-backed onto a Schmidt photographic survey, and he has also carried out survey programs on his own time. In addition to numerous discoveries of supernovae and near-Earth asteroids, Rob has (as of this writing) discovered 34 comets going back to 1987 -- the most named comet discoveries for any human being, ever. His best discovery, certainly, was the spectacular Comet McNaught C/2006 P1 (no. 395) which was visible in broad daylight in early 2007. Comet C/2005 L3 is the 9th comet I have observed which carries his name, and there are two inbound Comets McNaught which I have some reasonable expectation of adding to my tally within the not-too-distant future; I've already imaged one of these with CCD.
I should add, incidentally, that I consider Rob a personal friend, and I have dined with him both here in New Mexico and in New South Wales.
This Comet McNaught is presently near opposition and is about as bright as it will get. It is currently located in Ophiuchus near the star Zeta Serpentis, and is moving slowly towards the northwest. It should remain visible for another month or two before its motion away from Earth renders it too faint to be detected visually. After being in conjunction with the sun in early December it is at opposition again in late May 2008 and should be about as bright then as it is now, and should again be visually observable for two to three months. There is thus a reasonable possibility that this comet will end up being among the approximately 5% of the comets on my tally that I've followed for over one year.
Of all the comets I've observed, Comet C/2005 L3 has the sixth-largest perihelion distance, and the second-largest perihelion distance of any long-period comet (behind only Comet Skiff C/1999 J2 (no. 277) at 7.11 AU). When I first began observing comets in early 1970 no known comets had a perihelion distance this large; the largest-known was for Comet 29P/Schwassmann-Wachmann 1 (then varying between 5.4 and 5.5 AU) and the largest-known for a long-period comet was 4.71 AU. With the improved observational techniques and detection capabilities we have nowadays it is not too unusual for comets to be discovered out at these distances, but we are still probably only discovering a small fraction of the comets that are in this part of the solar system. (Comet C/2005 L3 is, intrinsically, a very bright comet, and would be a conspicuous naked-eye object were it to have a perihelion distance near or within 1 AU.) At this writing the largest perihelion distance of any known comet is 11.79 AU for the Centaur comet 167P/CINEOS (discovered in 2004) and the largest for a long-period comet is 11.43 AU for the Spacewatch discovery Comet Gleason C/2003 A2.
On a personal note, according to the most recent orbital calculations Comet C/2005 L3 passes perihelion on my son Zachary's 21st birthday. The only other comet on my tally that has passed perihelion on this date was Comet 85P/Boethin 1985n (no. 89), which did so exactly one year before he was born.
UPDATE: After it had been hidden behind the sun for the previous few months, I picked up Comet C/2005 L3 in the morning sky in mid-February 2008. It seems to be slightly brighter than it was last year, and if this trend continues it may become as bright as magnitude 13 1/2 when it goes through opposition in late May.
UPDATE: Perhaps a little bit surprisingly, Comet C/2005 L3 is still bright enough to be visually detectable (14th magnitude) in December 2008, after emerging into the morning sky following its recent conjunction with the sun. Over the coming months it tracks across northern Bootes and eventually enters Canes Venatici, and is at opposition in late April 2009. I do expect the comet to fade slowly, but it may remain observable for perhaps several more months.
With these latest observations, Comet C/2005 L3 becomes the 11th comet that I have followed for over 18 months. (Two of these are "returns" of Comet 29P/Schwassmann-Wachmann 1.) It is conceivable that I may still be able to observe it past the two-year anniversary of my first observation; if that happens, this would be only the 5th comet that I will have followed for that long a period of time.
I indicated in the previous entry that there were two inbound Comets McNaught that I had expectations of adding to my tally at some point in the future; this is one of them. It was discovered by Rob McNaught on April 17, 2007 during the course of the Siding Spring survey, at which time it was about 16th magnitude. This is the 10th comet I have observed with Rob's name on it, and since the previous entry he has discovered two more comets, bringing his lifetime discovered total to 36.
This is another very faint comet, being only 14th magnitude when I first observed it on the morning of July 19. As is often the case when I first pick up comets that are near the limit of my telescope's capability, I waited until I could obtain confirming observations on subsequent nights (in this case, on both of the next two subsequent mornings) before adding it to my tally. Fortunately, over the past few days we have had a bit of a respite from the stronger-than-usual monsoon season we've had this year in New Mexico, and I was able to have the clear mornings necessary to perform the confirmation observations. (That respite may be coming to an end as I write this, as it has already rained once today.) Curiously, despite the fact that July and August are usually the cloudiest months of the year in New Mexico, I have had unusual success in adding comets to my tally during those months; ever since my return to New Mexico back in 1986 only once have I failed to add at least one comet to my tally during the month of July, and with the addition of this comet I'm able to maintain that string for at least another year.
This latest Comet McNaught is presently a morning-sky object, located in southern Pisces and traveling slowly southward. By the latter part of August it enters western Cetus, where it remains for the next few months. It may get about a half-magnitude brighter than it is now during the latter half of September when it is near opposition, and will then probably fade beyond visual range within about a month or so after that.
According to the most recent calculations the comet has an orbital period of 7.02 years, which suggests that it should have been visually detectable, or at the very least discovered by one of the comprehensive sky surveys like LINEAR, during its previous return. However, it appears that the comet had a moderately close approach to Jupiter (0.57 AU) in January 2004, and prior to that it was in a larger orbit (period 7.8 years, perihelion distance 2.8 AU) than it is in now. The previous perihelion passage would have been in very late 1999, when it was poorly placed for observation; all the returns prior to that took place before the comprehensive surveys came on line. Meanwhile, the next return, in 2014, will be very similar to this year's, and if the comet maintains the same brightness I may very well be adding it to my tally then. (I will most likely be up to 500 comets by that time, I would think.)
On the personal front, as I indicated in an earlier entry I am a member of our local theatrical troupe (the Cloudcroft Light Opera Company, or CLOC) -- in fact, my entire family are members. During the summer months CLOC stages melodrama performances, and my younger son Tyler is a cast member of the current melodrama, entitled "Treachery at Cartilage Creek." Tonight is the final performance of the play, and since traditionally final performances are "gag night" when cast members play tricks on each other, I'm rather curious to see what they have in store this evening. My older son Zachary is home for the weekend, in part to see his brother's performance, so for the time being the entire family is together again.
We've just had another (brief) respite from our seemingly never-ending monsoon season here in the New Mexico mountains, and I've been able to add another comet to my tally -- continuing the surprising dominance that the monsoon months of July and August have had in this process. I first picked it up early in the morning of August 8 as a very faint object of 14th magnitude; just prior to my visual observation I had successfully imaged the comet with the Earthrise CCD system, and this was able to provide confirmation of my visual sighting.
While for the time being this is another of the very faint comets I've been adding lately, Comet Broughton won't stay that way, as it is still over a year away from perihelion passage, and should brighten substantially during the intervening time. This is only the seventh comet that I have observed in excess of one year before perihelion (a list that includes two returns of Comet 29P/Schwassmann-Wachmann 1) and is only the third long-period comet that I have so observed.
The comet was discovered via CCD back on July 17, 2006 by John Broughton, an amateur astronomer who resides and maintains a private observatory in Reedy Creek, Queensland. He has conducted his own survey program for several years, during which time he has discovered several hundred asteroids, among these being the "potentially hazardous" near-Earth asteroids 2004 GA1 and 2006 LD1. (I'll also add that several of the names he has given to his discovered asteroids are names that I, as a rock 'n roll music fan, can appreciate.) John has also discovered one earlier comet, a faint periodic object he found in October 2005 which was too faint for me to observe. At the time of his discovery Comet C/2006 OF2 did not appear cometary (hence its "asteroidal" designation), but its obvious long-period orbit suggested that it very likely is a comet, and in late September 2006 Carl Hergenrother utilized the 1.54-meter telescope at Catalina in Arizona to obtain CCD images which revealed its cometary nature.
Comet Broughton appears to be making its first visit into the inner solar system from the Oort Cloud. Gravitational perturbations from the planets have nudged it into a slightly hyperbolic orbit, and it is consequently being ejected from the solar system. This is thus the only visit that it will ever make to our corner of the universe.
The comet is presently near opposition, and is located in northern Capricornus, moving slowly towards the west. It crosses northward into Aquarius during early September and remains there for the rest of 2007; by the time we lose it in the dusk sky in January it may be a magnitude brighter than it is now. After being in conjunction with the sun in March it emerges into the morning sky by the latter part of May, being perhaps 11th or 12th magnitude then. Throughout the remainder of 2008 it should be an easy object to observe from the northern hemisphere, being located slightly north of declination +60 degrees and perhaps near 10th magnitude when nearest Earth (1.77 AU) in early December. After being in opposition late that month the comet should remain visible for the first few months of 2009, until we finally lose it due to faintness and location in the dusk sky around June.
I thus have the potential of following Comet Broughton for almost two years, a period of time roughly comparable to the intervals over which I followed Comets 1P/Halley 1982i (no. 85) and Hale-Bopp C/1995 O1 (no. 199). As we all know, and as was demonstrated by those two objects, a lot can happen, both in one's personal life and in the wider national and international arena, over that kind of time frame. I find it interesting to think about what all might happen between now and the time I am finished observing this comet, and in fact I can already envision what some of those things (including in my personal life) might be. As always, I'll comment on these as I (hopefully) continue to add comets to my tally during these next two years.
UPDATE: After Comet Broughton disappeared into evening twilight in early January 2008 I finally picked it up again in the morning sky near the end of May; it appeared about 13th magnitude, which is somewhat fainter than I had expected it to be. While it is probably still a bit too early to tell for sure, it appears that the brightness scenario I outlined above for the 2008-09 opposition may be a little optimistic; a peak brightness near 11th or 12th magnitude may be more reasonable.