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|During the course of its regular search efforts for near-Earth asteroids the LINEAR program based at White Sands Missile Range in New Mexico discovered on September 27 an "object" with an unusual motion, which CCD observations obtained elsewhere indicated was a faint comet. Orbital calculations by Brian Marsden at the Central Bureau for Astronomical Telegrams soon indicated that the comet was located at a rather distant 3.9 Astronomical Units (AU) (360 million miles, or 580 million km) from the earth and 4.3 AU (400 million miles, or 640 million km) from the sun. (1 AU = the average distance between the earth and the sun, or 93 million miles or 150 million km.) What makes this comet interesting, however, is that according to the preliminary orbit the comet is destined to come much closer to the sun and earth; Marsden's calculations indicate that it will be at perihelion (its closest point to the sun) on July 18, 2000, at a distance of 0.72 AU (67 million miles, or 108 million km) from the sun, and will be closest to the earth the preceding day, located only 0.37 AU (35 million miles, or 56 million km) away.
If one takes this orbit at face value one finds that this Comet LINEAR could possibly become a moderately bright naked-eye object during July. It will be well placed for observation from the northern hemisphere, being located in the northeast during the morning hours early in the month, and in the northwest during the evening hours late in the month. Around the 14th it passes between the earth and the sun, but will be well north of the sun and consequently will be visible both in the northwest during and after dusk and in the northeast during and before dawn. If the comet develops any kind of significant tail this placement could cause the tail to appear quite long in our sky. As an extra added bonus, moonlight won't be interfering very much with the comet's display; the moon will be in the evening sky early in the month and then, after full moon on the 16th, will be in the morning sky. (The eastern hemisphere will see a total eclipse of the moon on the 16th.)
The brightnesses of comets are notoriously unpredictable, and thus any forecasts of Comet LINEAR's brightness should not be taken very seriously at this time. An "average" forecast suggests that the comet could be about as bright as 3rd magnitude around the time of its closest approaches to Earth and the sun; this is about the same brightness as the "medium" stars in the Little Dipper and is what Comet Hale-Bopp exhibited in January 1997. Because it is traveling rapidly toward and then away from Earth during July its brightness may change fairly rapidly as well; forecasts suggest it might be about 5th magnitude (the faintest stars in the Little Dipper) both at the beginning and the ending of July. It is very possible that the comet could be significantly fainter, or brighter, than these forecasts, so prospective comet-watchers should be prepared for just about anything.
At this writing (early October 1999) Comet LINEAR is located in the constellation Auriga and is above the horizon throughout most of the nighttime hours. It is currently a very faint object -- about 16th magnitude -- and thus requires a relatively large telescope to be detected. Over the next few months it will move slowly into the evening sky and should gradually brighten, and by the time it disappears into sunlight around the middle of March 2000 it should be about 13th magnitude, i.e., bright enough to detect with larger backyard telescopes. It reappears in the morning sky around the end of May, and after making its passage by the earth and sun will be visible from the southern hemisphere during August, perhaps still bright enough to be detectable with binoculars. It will again be visible in the southern sky beginnning around November 2000 but by then should be quite faint.
This page will be updated as new information becomes available, and images of it may be posted once the Southwest Institute's telescope and CCD camera system are operational. Brightness measurements for Comet LINEAR and other comets can be found at the Comet Observation Home Page and at the International Comet Quarterly's web site.
|November 12, 1999
The latest orbital calculations by Brian Marsden indicate that comet LINEAR will pass perihelion on July 26, 2000, at a distance from the sun of 0.767 AU (71 million miles, or 115 million km) and will be closest to Earth on July 22, at a distance of 0.373 AU (34.7 million miles, or 55.8 million km). It passes some 45 degrees north of the sun on July 19, and is far enough north of the sun that it will be circumpolar -- i.e., never setting but instead remaining above the horizon continuously -- from mid-northern latitudes for several days around that date. Prior to July 19 it is better viewed in the northeast morning sky before dawn, and afterward is better viewed in the northwest evening sky after dusk.
Although still predicted to be quite faint, Comet LINEAR has as of this writing reached 14th magnitude, which is bright enough to be visible in large backyard telescopes. I've seen in on several occasions since the beginning of November. If the comet maintains this brightening trend up until perihelion at that time it could easily be brighter than the initial predictions given above. It may, in fact, reach 2nd magnitude, which is about the same brightness as Polaris (the north pole star) and the stars in the Big Dipper. If the comet does indeed get this bright and also develops a significant tail, it could become a rather impressive object. However, any predictions made at this point should be taken with a lot of caution, as the comet could do almost anything between now and perihelion.
|March 20, 2000
At this writing Comet LINEAR is entering into conjunction with the sun, and will remain invisible until it reappears in the morning sky around the end of May. My observations unfortunately indicate that the comet hasn't brightened at all since the beginning of 2000, and by the beginning of March it wasn't any brighter than the initial predictions for that time. Although the comet should still become a naked-eye object around the time of perihelion and closest approach to the earth, right now it seems unlikely that it will get any brighter than 4th or 5th magnitude (i..e., about the same brightness as the faintest stars in the Little Dipper). Still, anything can happen, and we should have a better idea of what to expect in about 2 1/2 months.
The most recent orbital calculations by Brian Marsden indicate that perihelion takes place on July 26, 2000, at a distance of 0.765 AU (71.1 million miles, or 114.5 million km) from the sun. The comet is closest to the earth on July 22, at a distance of 0.372 AU (34.6 million miles, or 55.7 million km). Marsden's calculations also seem to indicate that, unfortunately, Comet LINEAR is probably a first-time visitor into the inner solar system. Such comets, of which the infamous Comet Kohoutek of 1973-74 is the most notorious example, often have a tendency to be significantly less spectacular when close to the sun than are comets that have been around previously (such as Comet Hale-Bopp).
|CCD image of Comet LINEAR taken on January 28, 2000, by Marko Moilanen and Arlo Oksanen at the Nyrola Observatory in Finland.|
|June 4, 2000
Comet LINEAR has now reappeared in the morning sky, after being hidden behind the sun since March. It can be found in the constellation Triangulum, a couple of degrees west of the star Gamma Trianguli, and its brightness is near magnitude 10 1/2. The good news is that the comet has brightened quite a bit since it disappeared behind the sun in March, and in fact my observations show that it has already brightened noticeably since I first picked it up in late May. The bad news is that it is still quite a bit dimmer than expected (a little over one magnitude). Based upon what I'm seeing now, my prediction is that, while it should reach naked-eye visibility when nearest the sun and Earth in late July, it will almost certainly be nothing that could be considered a "Great Comet." Its peak brightness will probably be no brighter than 5th magnitude, i.e., the brightness of the faintest stars in the Little Dipper, which means that one will have to be in a fairly dark rural area and will have to know where to look in order to see it with the unaided eye. The conditions for visibility of the tail are quite good in late July, however, and if Comet LINEAR develops any kind of substantial tail its apparent length at that time could be quite long (20 degrees long or longer).
|June 26, 2000
With the moon now starting to clear out of the morning sky the next couple of weeks are prime viewing time for Comet LINEAR. It has continued to brighten rather nicely since early in June, and at this writing has reached a brightness of at least 9th magnitude. (I could see it in binoculars, despite fairly strong moonlight, over the weekend.) The comet is also starting to exhibit a moderately prominent tail, at least telescopically, although because this is still aimed almost directly away from us it is not especially long. Despite its continued brightening, however, the comet is still running quite a bit fainter than the original projections, so I still tend to think it won't get any brighter than 5th magnitude when it is brightest in late July. Although this is certainly bright enough for naked-eye visibility, this is nowhere near bright enough to where it could be called "conspicuous," and prospective comet-watchers will probably have to be located in dark rural environments and will have to know where to look in order to pick it up without optical aid.
Currently, Comet LINEAR is located in the far eastern region of the constellation Andromeda, a few degrees east of the star Gamma Andromedae. Over the next couple of weeks it will move to the northeast into the constellation Perseus, passing about 4 degrees northwest of Alpha Persei (Mirfak) during the second week of July.
|July 6, 2000
Although Comet LINEAR continues to brighten it has not done so as fast as we would have hoped, and as of this writing it has only brightened to 8th magnitude (easily visible, but not exactly conspicuous, as viewed in binoculars). At this rate, it is rather unlikely the comet will become any brighter than 6th magnitude (the limit of naked-eye visibility from a dark site) when nearest the sun and Earth later this month. The comet's tail has developed rather nicely, currently being about half a degree long (the diameter of the full moon) as seen in binoculars. Overall, the comet is a lovely object as seen through a telescope, but it may not become much more than that.
|July 18, 2000
Comet LINEAR is currently passing between the earth and the sun, although it is located far enough north of the sun such that it remains above the horizon all night as seen from north-temperate latitudes. Starting about now it is better viewed in the evening sky (in the northwest after dusk) than in the morning sky, which is fortunate because the moon has now cleared out of the evening sky. The comet has brightened to about 7th magnitude and is exhibiting a tail approximately one degree long, which is nevertheless far less spectacular than what we had originally expected; it seems unlikely that it will reach naked-eye visibility.
Several American comet scientists, including Alan Hale of the Southwest Institute, will be participating in an international comet conference being held in Esfahan, Iran, to coincide with the appearance of Comet LINEAR.
|July 24, 2000 (update written from Esfahan, Iran, at the International Scientific Conference)
Unless something unusual happens within the next week or so, Comet LINEAR is at its peak brightness. Unfortunately, it has not reached naked-eye brightness, and thus probably never will. Last night from outside Esfahan our group observed the comet as being perhaps slightly brighter than 7th magnitude, with a tail perhaps a degree long or thereabouts. (Other observers elsewhere in the world seem to be reporting about the same thing.) The comet has now passed its closest approach to the earth, and will be at perihelion (its closest approach to the sun) two days from now, and thus should start fading fairly rapidly. It is also traveling quickly southward, and those of us in the northern hemisphere will lose sight of it shortly after the beginning of August. It thus looks like our "Great Comet of 2000" (which, to be truthful, this object was never really expected to become) won't happen. Of course, there is still Comet McNaught-Hartley, which was originally expected to possibly reach faint naked-eye visibility around the end of this year, but according to the reports from the Southern Hemisphere this object also seems not to be brightening as has been expected. Anyone out there want to find the next bright comet??
|August 3, 2000
Comet LINEAR has pretty much disintegrated before our very eyes. Our first indication of this came in images taken with the Hubble Space Telescope in early July, which showed fragments starting to break off the comet's nucleus. By the last days of July the comet's central condensation, which had been quite prominent earlier, had split apart and existed as nothing more than a straight bar-like structure within the coma. (Some dramatic images of this are posted on the Comet Observation Home Page.) Even this has pretty much dissipated now, and the comet currently appears as little more than a diffuse, amorphous blob. There probably won't be anything to see before much longer.
Although this type of thing doesn't happen very often, such behavior in comets is not unprecedented. Oftentimes when something like this happens it occurs to a smaller fragment of a larger comet which has split up in the past. There is some speculation that Comet LINEAR might actually be such a fragment of a larger and brighter comet that may have passed perihelion centuries ago, although there apparently are no comets in our historical records which fit the bill. (This is not all that surprising, since after all the telescope was invented less than 400 years ago.)
Even without its apparent disintegration, as far as comet-watchers in the northern hemisphere are concernced Comet LINEAR is essentially gone. It is now very low in the western evening sky after dusk, and traveling southward quite rapidly; we'll lose it below our southwestern horizon before much longer. In addition, the moon is now moving into the evening sky, making observations even more difficult. Whether or not comet-watchers in the southern hemisphere will have anything to see of Comet LINEAR when the moon clears out later this month remains to be seen.
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