COMETS 411 - 420
|411. COMET 93P/LOVAS 1 Perihelion: 2007 December 17.35, q = 1.705 AU
Most people who know me personally know that I am nearsighted and have had to wear glasses since I was about 10 years old. My right eye, especially, is extremely nearsighted (approximately 20/400), and my left eye less so (about 20/50). Both eyes have been correctable to 20/20 and thus my nearsightedness hasn't presented too much of a problem in my life, and when it comes to visual observing through a telescope there hasn't been a problem at all, since all one has to do is adjust the focus accordingly. Earlier this year, however, I began to notice a distinct deterioration in my vision, especially in my right eye, to the point that I couldn't focus images in a telescope sharply no matter how much I adjusted it. A visit to my optometrist revealed that I had developed cataracts in both eyes, although significantly more severe in my right one.
A couple of centuries ago, such a condition might be a sentence to eventual blindness, but thanks to modern technology that is no longer the case; cataract surgery nowadays is a relatively quick and painless procedure. I successfully had cataract surgery on my right eye on September 4, and not only was the cataract removed, the lens implant has essentially corrected my earlier nearsightedness (I'm now seeing about 20/25 in that eye). That eye's vision through the telescope is now superb, and I can truthfully say that my overall astronomical vision is about the best it's ever been. I still have the cataract in my left eye, and should be having the necessary surgery within the next few months.
Thanks to the passage of the remnants of Hurricane Henriette over southern New Mexico, I had to wait a few days after my surgery before trying out my new right eye. On the first clear night I had afterwards, among other things I was able to add this faint comet to my lifetime tally. It was originally discovered in December 1980 by Miklos Lovas at the Konkoly Observatory in Hungary, the fourth of five comets (and first of two periodic ones) he discovered between 1974 and 1986. It currently has an orbital period of 9.2 years, and this year's return is the third predicted one since its discovery. At the discovery return it wasn't discovered until three months after perihelion passage and I didn't look for it then, but I observed it at both of the intervening returns, in 1989 (no. 132) and 1998 (no. 251). On the current return it was recovered on July 13, 2007 by the LINEAR program in New Mexico, on July 14 and 15 by "Countdown" mentor Vitali Nevski in Belarus, and on July 15 and 16 by Stas Korotkiy at the Crimean Observatory in Russia.
During both the 1989 and 1998 returns the comet was near opposition at the same time as perihelion, and reached a peak brightness between magnitude 12 1/2 and 13. The geometrical conditions aren't quite as favorable this year, with opposition taking place in early October a little over two months before perihelion, and thus it will probably remain somewhat fainter. It appeared as a tiny and dim object of 14th magnitude when I first picked it up on the morning of September 12, and it will probably reach a peak brightness between magnitude 13 and 13 1/2 during November before fading beyond visual range by about the end of this year. Throughout this time it will be traveling through northern Pisces and south central Andromeda and thus, although faint, is conveniently accessible for observation.
In mid-September I was attending the 1st Annual Southwest Night Sky Conference in Taos, New Mexico to give a talk about Earthrise. While preparing my presentation the night before, my laptop computer -- which, among other things, contains all the data for this web site -- experienced a catastrophic motherboard failure. (I ended up "winging it" during my talk the next day.) It took me three weeks before I could get the problem fixed, and during that time I managed to add this new comet to my tally -- which I guess goes to show that, no matter how dependent we might become on modern technology and how lost we are without it, at least the night sky is still there for us.
This comet has the potential to be a fairly bright and interesting one, and I hope a large number of Earthrise students are able to view it. It was discovered on March 19, 2007 by the Lowell Observatory Near-Earth Object Search (LONEOS) program based in Flagstaff, Arizona, a comprehensive sky survey program that became operational in 1993. Although perhaps not quite as prolific in discoveries as some of the other programs, LONEOS has nevertheless discovered quite a few near-Earth asteroids as well as several comets since then; this is the 7th LONEOS-discovered comet, and the fourth with the name "LONEOS," that I have observed.
At its discovery Comet LONEOS was a very faint object of 19th magnitude, and in fact didn't appear cometary on the initial discovery images (hence the name "LONEOS" as opposed to the actual person who discovered it). Its small perihelion distance made it an object of interest right away, but it remained faint and didn't brighten by much more than a magnitude by the time it disappeared into sunlight around mid-year. After being in conjunction with the sun in mid-September it began to emerge into the morning sky, and observers who began viewing it from high northerly latitudes reported that it was actually brighter than predicted. When I first picked it up on the morning of September 22 -- very low above the northeast horizon, in twilight -- it was almost as bright as magnitude 9 1/2, about 1 1/2 magnitudes brighter than the original expectation for that time.
If Comet LONEOS maintains this trend, we could be in for a pretty good show near the end of October. It is presently a morning-sky object (although still fairly low in the northeast near the beginning of dawn), but in mid-October it again goes through conjunction -- 30 degrees north of the sun -- and moves over into the evening sky. It then begins to head south fairly rapidly, and its elongation also decreases, to a minimum of 20 degrees right around perihelion (when it will also be nearest Earth, 0.72 AU). If the comet remains 1 1/2 magnitudes brighter than originally expected, it may be about magnitude 5 1/2 or 6 when it becomes an evening-sky object, and perhaps as bright as magnitude 3 1/2 to 4 at the end of the month.
At that time the comet is traveling southward at three degrees per day, and shortly after the beginning of November the northern hemisphere will lose it. From that point the southern hemisphere should have a reasonably good view of it as it recedes from the sun and Earth and (presumably) fades, although the elongation remains fairly small (being at a maximum of 34 degrees in late November). The comet enters southern circumpolar skies by early December, is in conjunction with the sun late that month, and may still be visually detectable in larger telescopes for perhaps the first few weeks of 2008.
Most of the comets I've listed in "Countdown" so far have been faint and unimpressive objects. Comet LONEOS, which has the potential of being a naked-eye object, should be a notable exception to that trend, and moreover will be conveniently visible in the evening sky when brightest. I encourage all potential "Countdown" participants to take advantage of this opportunity to view this visitor from the outer solar system.
Rob McNaught does it again! He discovered his 38th named comet on October 9, 2007, during the course of the regular program of the Siding Spring survey in New South Wales; it was quickly confirmed by several observers around the world during the subsequent hours, and the discovery was announced later that same day. I was able to observe it on the evening of October 9, less than 16 hours after Rob's discovery. (This is the 11th comet I've observed that he has discovered.) At the time of my observation the comet was located in southern Ophiuchus in the southwestern sky during the early evening hours, and was about magnitude 11 1/2.
At this writing, the available orbit for this newest Comet McNaught is very preliminary, and the "true" orbit could end up being quite a bit different. (We should know more within about a week as more positional information becomes available and the orbit gets better defined.) According to this preliminary orbit, the comet will be traveling towards the south-southwest and the northern hemisphere will lose it around the beginning of November, by which time it may be two to three magnitudes brighter than it is now. Around the time of perihelion the comet will be in conjunction with the sun, about 18 degrees directly south of it; since it may be around 5th or 6th magnitude then observers in the southern hemisphere may still be able to follow it. After perihelion the comet comes back north, and becomes visible to the northern hemisphere again (in the morning sky) by early December; depending upon how it fades it could remain visually detectable until sometime in January or February 2008.
Over the years I've noticed, though, that for comets with this small a perihelion distance, brightness "predictions" don't necessarily mean all that much. It is entirely possible that Comet McNaught could end up becoming much brighter than this (perhaps as a result of splitting of its nucleus) or, on the other hand, it could disintegrate and fade away entirely by the time it passes perihelion. Indeed, there is already some indication that its brightness isn't behaving "normally;" based upon the brightness it is currently exhibiting it should have been discoverable by the various operating surveys for the past few months but, for some reason, wasn't detected. On the other hand, as I've indicated above the orbit we currently have available may not be correct, and the comet's brightness behavior may be more mundane. This is one of those cases where all I can say is, "stay tuned!"
As for what's going on around here, well, autumn definitely appears to have arrived in the southern New Mexico mountains; there is a definite crispness in the air, and both the days and the nights have been quite beautiful lately. (This has always been my favorite time of the year.) I'm gearing up for the expected decent display of Comet LONEOS C/2007 F1 later this month, and will be conducting some "Countdown"-related teacher workshops and observing sessions as that object makes its appearance. I'm also preparing the exhibit I'll have at the Wirefly X-Prize Cup's Education Day activities a little over two weeks from now. From a purely personal standpoint, I've happy that my favorite football team, the Dallas Cowboys, won an exciting game earlier this week, although they've got a very big and difficult game coming up next weekend. Cloudcroft High School, which my son Tyler attends, is having its homecoming football game this weekend, and Tyler has been nominated for sophomore homecoming prince. He actually won the voting for freshman homecoming prince a year ago, and we'll have to see if he can repeat the feat this year. (We won't know the voting results until the game on Saturday.)
A piece of meaningless trivia: I commented in an earlier entry that, in the new comet discovery designation scheme that was introduced at the beginning of 1995, the letter "G" (i.e., discovery in the first half of April) is the only letter for which I have yet to observe a comet. By contrast, the letter "T" (discovery in the first half of October, directly opposite to "G") is my most "successful" letter so far: this Comet McNaught is the 16th comet I have observed to be assigned the letter "T" in the new scheme. Furthermore, 2007 is the 7th year in a row (and 10th year of the past 11) which has produced at least one "T" comet that I've observed. While there are perhaps a few minor selection effects operating (e.g., weather conditions at the main discovery sites, etc.) such "clumpiness" is nevertheless consistent with an overall random distribution.
UPDATE: A new orbit has now been calculated for Comet McNaught, and perhaps not too surprisingly, it differs drastically from the early preliminary orbit. It also makes for a much less interesting comet, especially for those of us in the northern hemisphere. The comet continues heading south, and we northerners will probably lose it, perhaps for good, in early November. It is in conjunction with the sun in early December, and by the end of the year is in southern circumpolar skies, and near its peak brightness of perhaps 10th magnitude. At the beginning of February 2008 it travels as far south as declination -87.5 degrees before heading back north, and not until March does it come far enough north to be accessible again to observers at my latitude. It might possibly be 12th or 13th magnitude then, but it will probably fade from view not too long thereafter.
UPDATE: After perihelion and conjunction with the sun, Comet McNaught was an unexpectedly bright 8th magnitude when it became visible in the southern hemisphere's morning sky near the beginning of 2008. After its journey through southern circumpolar skies it became accessible again from my latitude near the end of February, still at a moderately bright 11th magnitude. It will probably remain visible for perhaps another month or so.
On Wednesday morning, October 24, I had arisen early in order to travel to Las Cruces, New Mexico to attend the International Symposium on Personal Spaceflight (about a two-hours' drive). Just before I planned to leave I decided to check my e-mail, and there were some postings on the Comet-Images Yahoo! group (of which I'm a member) about a large outburst of this comet, up to 7th magnitude. Since it was still dark here I decided to check it out -- and wow! The comet was even brighter (about 4th magnitude) and easily visible to the naked eye. I ended up being about an hour late for the conference, which was OK since I was simply an attendee and not speaking -- and I was able to make one of the most unique cometary observations I've ever made.
This comet was discovered back on November 6, 1892 by a British amateur astronomer, Edwin Holmes, who was observing from London -- probably not possible much these days. The comet was a naked-eye object of 4th magnitude located near the Andromeda Galaxy M31, and it soon became apparent that Holmes had discovered it shortly after the onset of a major outburst. It retained its brightness for a few weeks, gradually expanding in size until its coma spanned a full thirty arcminutes (half a degree) across by the end of November. It then began to fade rapidly in early December, but underwent another large outburst (at least five magnitudes) in mid-January 1893. Spectra taken at the time indicate that the coma (and thus the outburst events that produced it) was made almost entirely of dust.
Comet Holmes was found to have an orbital period of approximately 7 years (currently, 6.9 years) but has remained faint ever since then; in fact, it was "lost" following its return in 1906. As a result of a detailed 1963 study by then-Yale University graduate student (now Director Emeritus of the Minor Planet Center) Brian Marsden, Comet Holmes was finally recovered at its 1964 return by Elizabeth Roemer at the U.S. Naval Observatory's station in Flagstaff, Arizona. It remained a very faint object of 19th magnitude during that return, and while it has since been recovered at every subsequent return, it has never appeared any brighter than 17th or 18th magnitude.
On its return this year Comet Holmes was recovered on May 13 by two Italian astronomers, Ernesto Guido and Giovanni Sostero, utilizing a remotely-controlled telescope in Mayhill, New Mexico. They reported it as being about 15th magnitude (with other observers subsequently reporting something similar), which was bright enough to suggest it might be visually detectable; I tried on a few occasions, but never saw anything convincing. Since the comet was already past perihelion it has gradually faded since then, and recently wasn't any brighter than about 17th magnitude.
Early on October 24 a Spanish astronomer, Juan Antonio Henriquez Santana, reported the comet as undergoing a major outburst, which was quickly confirmed by several other Spanish astronomers (Gustavo Muler, Ramon Naves, and Montse Campas) -- as I've indicated above, they all reported it as being about 7th magnitude. By the time I saw it a few hours later, it had brightened an additional three magnitudes, and it still wasn't done; several observers to my west reported it as continuing to brighten, and when I saw it late that evening (after my return from Las Cruces) it had almost reached magnitude 2 1/2, and was easily visible to the naked eye despite the almost full moonlight. At this writing the brightening seems to have stabilized, although it's still pretty early yet. Even at this point, though, this appears to be the largest cometary outburst ever observed -- an increase in brightness by a factor of over 600,000.
When I first observed the comet on the morning of the 24th it appeared entirely stellar, even in a telescope. As of a day later it is exhibiting a small, but very bright and sharp coma that is expanding by the hour; during the course of the night of October 24-25 I saw it grow from 1.2 arcminutes in diameter to 1.5 arcminutes. If, as seems fairly likely, we are seeing some sort of repeat of the 1892 outburst the coma will likely continue expanding over the next two to three weeks, and with the moon's leaving the evening sky within a few days the comet itself should remain an easy naked-eye object for some time.
The comet is currently located in central Perseus, about 4 1/2 degrees east of the bright star Alpha Persei, or Mirfak. It is traveling very slowly almost due westward, and is at opposition in mid-November. It remains in this part of Perseus for some time, and passes about 20 arcminutes north of Alpha Persei itself on the night of November 18-19. It's hard to know what to expect; if we do get a repeat of the 1892 activity it should remain visible to the unaided eye for at least another two to three weeks, perhaps longer. We should perhaps keep in mind that there was a second outburst at P/Holmes' discovery return; if that were to happen again this time then perhaps that outburst would occur near the end of this year. The comet will still be in Perseus then, in the western part of the constellation about 2 1/2 degrees west of the star Kappa Persei and four degrees north-northwest of the "demon star" Algol.
Happenings like this outburst of 17P/Holmes are a large part of the charm and mystique of comet observing, and are what keep me observing these things year after year after year. I couldn't be more pleased with the timing; the Wirefly X-Prize Cup is this weekend, and Earthrise will have an exhibit (which, among other things, will include a Starlab portable planetarium), and we will definitely be including Comet Holmes, and "Countdown," as a part of that. The X-Prize Cup is at Holloman Air Force Base this year -- practically right on my doorstep -- and in any event it feels very satisfying to be a part of such a celebration of humanity's future potential.
UPDATE: As of early November Comet Holmes' brightness has pretty much stabilized for the time being, between magnitudes 2 and 2 1/2. It has continued to expand, with an inner coma now about 15 arcminutes in diameter, and an outer "halo" well over half a degree across. Depending upon what types of instruments are used to examine it, the comet shows a variety of structure over both large-scale and small-scale distances, from "dust stream" detail within the innermost regions of the coma, to a wide series of "tails" extending from the outer halo.
There has, certainly, been a lot of speculation as to what has caused this incredible outburst of Comet Holmes (and keeping in mind the fact that it underwent a similar event at its discovery in 1892). Comet scientist Zdenek Sekanina (based at the Jet Propulsion Laboratory in California) has proposed that the outburst may have been due to a companion nucleus being jettisoned from the primary nucleus, and then undergoing a "cataclysmic" disintegration. We'll have to see how well this explanation (or any other) holds up as time goes by and the comet's activity unfolds.
UPDATE: On November 15 the Space Telescope Science Institute released some images of the central coma of Comet 17P/Holmes that have been taken with the Hubble Space Telescope. We've included one of these images in our image gallery, and additional images and information are available at the official Hubble site.
The comet continues to be a conspicuous naked-eye object, although it has faded by perhaps half a magnitude from its peak brightness early in November. The inner coma is now up to 30 arcminutes in diameter (the apparent size of the full moon) and the outer halo (now very faint) is over a degree across. The comet's overall evolution since its outburst is quite similar to that it exhibited during its 1892 outburst.
With all the current hoopla going on over Comet 17P/Holmes, it is easy to forget that there are other comets in the sky. This one in particular, though, is worth keeping an eye on, because it will likely become an interesting and noteworthy object in its own right within a couple of months. I first saw it on Halloween evening (October 31), during the last hour of the month of October; at that time it was a dim and somewhat difficult object near magnitude 13 1/2, but it won't be staying this faint for much longer.
This comet was discovered in January 1858 by Horace Tuttle, an American astronomer then based at the Harvard College Observatory in Massachusetts. Tuttle discovered several comets during the 1850s and 1860s, including four numbered periodic comets (all of which I've observed at least once), and later went on to have a colorful career in the U.S. Navy during the American Civil War and subsequently surveying the American West with the U.S. Geological Survey. The comet was soon found to be periodic, and in fact was found to be identical to a comet discovered in January 1790 by the French astronomer Pierre Mechain, a friend and sometimes competitor of Charles Messier (who compiled the catalogue of Messier deep-sky objects that is so familiar to astronomers today).
Tuttle's comet has an orbital period of slightly under 14 years (currently, 13.6 years), and its orbit has an unusually steep inclination of 55 degrees. Since its discovery by Tuttle in 1858 it has been recovered at every return except one; including Mechain's return in 1790 the current return is the 12th at which it has been observed. It is the parent comet of the Ursid meteor shower that peaks around December 22 every year; this is normally a weak shower producing about 10 meteors per hour, but on occasion has produced brief but significantly stronger displays.
I've seen this comet once before, during its return in 1980 (no. 40). That happened to be a very favorable return, as it passed 0.49 AU from Earth in early December and reached magnitude 6 1/2 when near perihelion near the middle of that month. I vividly remember that return, in part because of the display it put on -- during my final observation, just before it disappeared below my southern horizon, it was a striking object with a degree-long tail in binoculars -- and in part because of what I was going through in my life at the time. Earlier that year I had graduated from the U.S. Naval Academy, and during the summer I had purchased a 20-cm (8-inch) Meade reflecting telescope as a graduation present to myself. (I still have this telescope, by the way, and still use it on occasion.) During that fall I was attending Surface Warfare Officer's School (SWOS) at the Naval Amphibious Base in Coronado, California, and I would regularly drive into the mountains east of San Diego to observe with that instrument -- an escape, of sorts, from the emotional turmoil I was experiencing with my day job. Comet Tuttle is one of the first comets I showed my then-girlfriend now-wife Eva, and is also one of the two comets I observed the night that John Lennon was murdered. (Like many Americans, I had learned of Lennon's death while watching the Monday Night Football game that evening, and I can still remember the almost surreal atmosphere in my car as the radio station I was listening to played nothing but Beatles and John Lennon songs during my drive up to the mountains and back.)
Comet Tuttle also returned to perihelion in 1994, but this was an extremely unfavorable return (being in conjunction with the sun when at perihelion) and very few observations of any kind were made. I attempted it on a couple of occasions but was not successful in seeing it.
On the current return P/Tuttle was recovered on April 22, 2007 by Carl Hergenrother with the 1.5-meter telescope at Catalina Observatory in Arizona. It was then very faint (20th magnitude) and has brightened very slowly since then. For the past few months it has remained high in the northern circumpolar sky -- passing only a degree and a half from the north celestial pole in mid-October -- and when I first saw it on Halloween night was still at a declination of +86 degrees, being located 2 1/2 degrees from Delta Ursae Minoris (the first star in from Polaris in the "handle" of the Little Dipper). It remains north of declination +80 degrees until early December, by which time it should have brightened to perhaps 9th magnitude.
During December Comet Tuttle races rapidly southward through the constellations of Cassiopeia and Andromeda, and on New Year's Day 2008 it passes 0.25 AU from Earth -- by which time it will be in Pisces, traveling southward at four degrees per day, and (based upon its brightness in 1980) a dim naked-eye object between 5th and 6th magnitude. As it pulls away from Earth it will probably begin fading; meanwhile it continues its rapid southward trek, becoming invisible from my latitude by perhaps early February, and entering southern circumpolar skies by mid-March. Southern hemisphere observers may be able to follow it until April or perhaps May.
So, I have another good return of P/Tuttle to look forward to, similar to -- even somewhat better than -- that return I remember so well from 1980. While I don't want to speculate too much right now, it is conceivable that this return could also see some interesting developments in my personal life -- to an extent, possibly bookending some of those that came with that first return. We'll see what happens . . .
Since the appearances of comets in our skies are random, it sometimes happens that two or more periodic comets will be making favorable returns at around the same time. A case in point is this object, which is having a good return at the same time as the above comet; it won't be quite as bright but it nevertheless should be an easy object to observe around the time of perihelion passage.
Comet 46P/Wirtanen was discovered in January 1948 by Carl Wirtanen, an astronomer based at the Lick Observatory in California. (This was the first of three comets he discovered that year, and overall there were 11 new comet discoveries in 1948 -- a record for the time.) At that time the comet had an orbital period of 6.7 years and a perihelion distance of 1.63 AU, however some intervening close approaches to Jupiter (0.28 AU in 1972, and 0.47 AU in 1984) have shortened both of these quantities dramatically. The current orbital period is 5.4 years. Incidentally, this was the originally planned destination of the European Space Agency's Rosetta mission, however because of some difficulties with the Ariane 5 launch rocket the Rosetta launch was delayed for a year; this successfully took place in March 2004, and Rosetta's current destination is Comet 67P/Churyumov-Gerasimenko (which, incidentally, I've seen on three returns).
Following its 1984 approach to Jupiter, 46P/Wirtanen has become bright enough to be visually observable at every subsequent return, and in fact I have seen it at each of those: in 1986 (no. 92), 1991 (no. 162), 1997 (no. 224), and 2002 (no. 316). The returns have alternated between being visible in the evening sky (1986, 1997, and the current return) and the morning sky (1991 and 2002). Curiously, during each of the evening-sky returns it has had to share the sky with a bright naked-eye comet; in 1986 it was 1P/Halley 1982i (no. 85), in 1997 it was Hale-Bopp C/1995 O1 (no. 199), and of course this time it is with 17P/Holmes (no. 414).
This is thus the fifth return I have seen of 46P/Wirtanen, and it becomes only the fourth comet I have seen on five returns (after 2P/Encke, 81P/Wild 2, and 41P/Tuttle-Giacobini-Kresak). It was recovered on August 4 and 5, 2007 by Luca Buzzi and Federica Luppi at the G.V. Schiaparelli Observatory in Italy, and independently by Australian amateur astronomer David Herald in Kambah, A.C.T. on August 6. I first suspected it on the evening of November 1 as a very faint and diffuse object, that unfortunately was located close to a bright star which made verification difficult; I successfully confirmed it the following night at slightly fainter than 13th magnitude.
The comet is currently located fairly low in my southern sky, in the constellation Piscis Austrinus at a declination of -31 degrees. Over the coming weeks it gradually moves north and east, and also brightens; by the end of this year it will be located in Aquarius and perhaps as bright as 10th magnitude. It remains near an elongation of 67 degrees in the evening sky throughout all of January and most of February, moving northward the whole time; when at perihelion it will be in Pisces and probably at least 9th magnitude, possibly 8th. It is closest to the earth (0.92 AU) in mid-February, and after that should begin fading, all the while continuing its northward trek (to a maximum northerly declination of +35 degrees in early April). I should be able to follow it for at least that long, possibly into late April or early May.
This turns out to be the most favorable return of 46P/Wirtanen ever since its original discovery. The next return, in 2013 (perihelion in early July), is very unfavorable and the comet probably won't be visually detectable, however the return after that, in 2018 (perihelion mid-December), is excellent; it passes 0.078 AU from Earth that month and may become as bright as 4th or 5th magnitude. We won't quite see anything like that from this comet again, and in 2042 it again passes close to Jupiter (0.56 AU) and its orbital period increases to 5.8 years and its perihelion distance to 1.22 AU. Let's enjoy the show while it lasts!
And the comets keep coming . . . The addition of three comets to my tally within a span of four nights (and four within a span of a week and a half) is unusual but not unprecedented; I once added three comets to my tally within the course of a single night. I first picked up this comet on the morning of November 4, as a very faint object of 14th magnitude.
Unlike the other recently-added comets, this one is a long-period object -- its orbital period being almost exactly 1000 years -- although its orbital inclination of 10 degrees is unusually low for a long-period comet. It was discovered back on September 28, 2006 by Rik Hill with the Catalina Sky Survey in Arizona. This is the fourth of six comets that he has discovered (or, at least, have been named for him) so far, including another comet (a very faint periodic object, P/2006 S6) that he discovered on the same night. I have successfully observed one of his other comets, LONEOS-Hill P/2005 XA54 (no. 386).
This is probably going to remain a rather faint comet, however it will at least be favorably placed for observation for the next few months. It is currently an early morning-sky object located in Gemini a little over four degrees south of the bright star Pollux and, a little curiously, only about 15 degrees east of Mars, which is now getting poised for a favorable opposition next month. It remains in this same part of the sky for the next several weeks, initiating its apparent retrograde (westward) motion in mid-December and being at opposition in mid-January 2008. The comet should be brightest during the first half of January, being perhaps a half-magnitude brighter than it is now (i.e., between magnitudes 13 and 13 1/2). It will presumably begin fading after that and should remain visually detectable until perhaps sometime in February.
Although the comet activity is high right now, things have otherwise settled down for me a bit now that the Wirefly X-Prize Cup is over. The biggest challenge for me at the moment is fundraising, since Earthrise has until the end of this year to meet the $100,000 matching grant challenge that was presented to us by Anousheh Ansari. We've got a couple of events planned over the coming weeks and are working on others; if we are successful in this challenge then that means we should be able to begin development of our dark-sky site (which will include, among other things, a fully-operational telescope that can be used for imaging "Countdown" comets and, hopefully, a large telescope for our PlanetQuest collaboration) as well as Earthrise Radio and all the other great things I've been envisioning for Earthrise.
The busy autumn of 2007 comet-watching continues, with the addition of this rather faint comet that I had thought I might see, but was starting to have my doubts. It was originally discovered in October 1951 by Sylvain Arend in the course of a photographic patrol program being conducted at the Royal Observatory in Uccle, Belgium; this was the second of three comet discoveries by Arend, who also found another periodic object (49P/Arend-Rigaux, which I've observed at two returns and may possibly add again during "Countdown" during its return in 2011) and Comet Arend-Roland 1956h, which became a conspicuous naked-eye object during the first half of 1957.
The discovery return in 1951 was a very favorable one from a geometric standpoint, and it was reported as being about 14th magnitude. Subsequent returns were less favorable, and a distant encounter with Jupiter in 1969 placed it into an orbit with a period of exactly 8 years that continuously brought it to perihelion when on the far side of the sun from Earth, thus keeping it a distant and faint object that was difficult to observe. Finally, another distant encounter with Jupiter in 1993 increased the orbital period to 8 1/4 years and also increased the perihelion distance somewhat, but on the other hand took the comet out of that repetitious situation and created the possibility that I might be able to detect it visually someday. The extremely favorable geometry in 2007, with opposition taking place in late October just prior to perihelion, seemingly presented such an opportunity.
Comet 50P/Arend was recovered on July 16, 2007 by Italian astronomers Ernesto Guido and Giovanni Sostero, utilizing a remotely-controlled telescope in Mayhill, New Mexico. I began trying for it in early October, but all my attempts were unsuccessful up through the time of perihelion passage, leading me to think that I probably wouldn't see it after all. However, on the evening of November 11 -- my brother Barry's birthday, incidentally -- I successfully picked it up as a very faint object slightly fainter than 14th magnitude.
The comet is currently located in eastern Andromeda, three degrees north of the prominent double-star Gamma Andromedae (or Almach), and is moving towards the northwest. Theoretically, it is as bright as it is going to get, however it is conceivable that it might exhibit some asymmetry in its light curve with respect to perihelion, a feature seen in some other periodic comets (notably 6P/d'Arrest, 10P/Tempel 2, and 26P/Grigg-Skjellerup -- the first and last of these will be returning to perihelion in 2008 and will almost certainly be included within "Countdown"). If this happens, 50P/Arend may be visible for another month or so before it begins fading away; if not, then another observation or two this week will probably do it for me. In any event, it is rather rare for me these days to observe an already-numbered periodic comet that I haven't seen on an earlier return, and I'm glad that I was able to add this particular comet to that tally.
I knew that this fall would be a busy time for comet-watching. There were quite a few inbound comets that I expected to pick up around this time, and several of the recently added comets are in this group; there have also been a few surprises, including Comet 17P/Holmes, which at this writing continues to be a conspicuous naked-eye object. It has helped that the weather here has been especially clear and dry during recent weeks, a rather distinct reversal from what we've had earlier this year.
This comet is one of the surprises, and is one I never expected even to look for, let alone see. However, even for the comets that I don't expect to observe I keep a watch on the published CCD magnitudes on the weekly "Observations of Comets" Minor Planet Electronic Circulars (MPECs) published by the Minor Planet Center (such as this recent one), and occasionally I will notice magnitudes that are bright enough to suggest that a particular comet might be worth attempting. Such was the case with this object.
The comet was discovered on July 10, 2007, by Rob McNaught during the course of the Siding Spring survey in New South Wales; initially it was a seemingly nondescript 18th magnitude object. It was soon found to be periodic, with an eventually determined period of 6.6 years. Following this, Syuichi Nakano in Japan determined that McNaught's comet is identical to a previously-unreported comet that appeared in images taken by the Near-Earth Asteroid Tracking (NEAT) program's Haleakala (Maui), Hawaii telescope in August and November 2000; the LONEOS program in Arizona also recorded images in August 2000, and amateur astronomers Maik Meyer in Germany and Reinder Bouma in The Netherlands later identified the comet in additional NEAT images taken in September and December 2000, and in images taken by the LINEAR program in New Mexico and by the NEAT Palomar telescope in January 2002. This comet (which passed perihelion in January 2001) has retroactively been assigned the designation P/2000 P3, and meanwhile the identification allows the comet to be assigned the periodic comet number 191P.
The comet was at opposition in early November, and since it is already two months past perihelion it is theoretically about as bright as it is going to get. After noticing the recent CCD magnitude measurements I decided to try for it on the evening of November 11, and did suspect something; however, it was located in a poor star field and I wasn't able to confirm (or refute) this potential observation. Two nights later, under excellent sky conditions I clearly saw the comet, including distinct motion over a one-hour interval, which confirms the suspect I had on the 11th. The comet was a very faint object of magnitude 14 1/2; like with the previous comet, I very possibly may never have been able to have seen it if I hadn't have had the recent cataract surgery I underwent back in September.
Comet 191P/McNaught is currently located in northeastern Cetus, about three degrees southeast of the star Gamma Ceti, and is accessible all night. It is moving slowly towards the west-northwest, reaching its stationary point and resuming direct (eastward) motion in mid-December, and thus remains in this section of Cetus through the remainder of this year. Unless it exhibits a distinct asymmetry in its brightness behavior, I probably won't be following it for very long; this week's observations might very well be the only ones I obtain.
The confirmation of my suspected observation of this comet on the evening of November 11 means that I successfully added two comets to my tally on that night. This is the first time since February 2004 that I have added two comets in the same night, and the 16th time overall that I have accomplished this feat (in addition to the one occasion in December 1993 when I added three comets in one night). I have also added six comets to my tally within the past three weeks, which makes the recent past one of the busiest such intervals I've ever had. (My record for "busiest comet adding interval" was a six-week period in the late summer of 2002 when I added nine comets to my tally.) Meanwhile, there are still a few inbound comets that I might potentially add within the not-too-distant future, so the current busy period may not quite be over yet. Considering that a year ago I went over 3 1/2 months without adding any comets to my tally, this illustrates yet again that the appearances of comets in our skies are random.
Yet another comet! And another Comet McNaught! This is the 13th comet I've observed that carries Rob McNaught's name, which currently ties him for 5th place among the names that appear most often on my tally. (His overall discovery total, incidentally, still stands at 38 as of this writing.) Unlike the previous comet, I was expecting this one, in fact, this is one of the comets I was referring to in an earlier entry when I remarked that there were still inbound Comets McNaught I was expecting to see at some point. As of right now there aren't any additional McNaught comets that I have expectations of observing, but of course Rob continues to remain very active and I have little doubt that I will continue to see his name from time to time in my tally.
Rob discovered this comet as part of the regular program of the Siding Spring survey in New South Wales as long ago as August 20, 2006 -- less than two weeks after his discovery of the spectacular comet C/2006 P1 (no. 395). At that time the comet was 6.8 AU from the sun and almost two years away from perihelion, and a relatively dim object of 18th magnitude. It was at opposition in early December 2006, and earlier this year I made a few visual attempts for it; while these were unsuccessful, I did succeed in recording it on a couple of CCD images I took in early March. After being in conjunction with the sun in late June it has begun emerging into the morning sky over the past couple of months, although at a fairly high southerly declination that has made it a rather difficult object to access from mid-northern latitudes. It has now finally emerged high enough that I could try for it, and on the morning of November 15 (when its declination was -42 degrees) I successfully observed it as a 13th magnitude object when it was directly above my southern horizon.
Intrinsically, this comet is a bright one, but its large perihelion distance will keep it from becoming a bright object in our skies. It is currently located in the constellation Vela and is traveling towards the southwest, and the increasing southerly declination will continue to make it a difficult object to observe from the northern hemisphere (although it will be easily accessible from the southern). It travels to as far south as declination -51.7 degrees in late January 2008, and when at opposition in mid-February will still be at -50.5 degrees. After that the comet begins to head more northward, and those of us in mid-northern latitudes should have our best views between April and June (when its declination goes from -38 degrees to -9 degrees). It should also be at its brightest around this time, about 11th magnitude.
After that we will begin to lose the comet in the evening twilight, and it is in conjunction with the sun in mid-October. If it maintains its brightness it's possible we'll be able to see it again near the end of the year when it emerges into the morning sky (now at a more convenient declination of +4 degrees), and we may be able to follow it for the first few months of 2009. Conceivably, the comet could still be about 14th magnitude when at opposition in late May, but it will probably begin to fade fairly quickly after that. In any event, this could well turn out to be another comet that I end up following in excess of one year.
Comet McNaught is not the only current interesting morning-sky southern object. On the same morning that I first picked it up I also obtained my first observation of the new Nova Puppis 2007, which had been discovered the previous day, and which was located 15 degrees to the northwest of the comet. Although the initial reports indicated that the nova was as bright as magnitude 6 1/2, when I saw it it had already faded to magnitude 8. This appears, then, to be a rather fast nova -- somewhat in contrast to the other transient celestial object in the southern morning sky.
UPDATE: Pretty much as expected, I picked up this comet in the morning sky in late December 2008, and it appeared at about 13th magnitude -- consistent with the scenario described above. It is indeed possible that I may be able to follow it until perhaps May 2009, although probably not much beyond that.