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The Great Christmas Comet of 2011, 2011 W3 (Lovejoy)
Mongo
post Dec 27 2011, 02:54 AM
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Comet-ml post #19122 by Vello Tabur

QUOTE
Hi,

I concur with the descriptions provided by others this morning. Although the comet has faded significantly, it still remains an easy naked eye object. From a dark-sky site near Boorowa, NSW, the tail was fainter than the nearby Milky Way and is now only slightly brighter than the SMC. There is no sign of the ion tail and the dust tail appears slightly narrower than on my last observation 2 days earlier. Visually, I could only trace the tail to the same altitude as midway between alpha/beta Centuri but, the wide-field image below hints at a continuation toward Crux, as noted by David S.



Vello
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Mongo
post Dec 27 2011, 05:49 PM
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From comet-ml post #19128 by Michael Mattiazzo:

QUOTE
The tail is noticeably fainter than 2 mornings ago, however it is still growing as the comet approaches Earth. Closest on Jan 8 at 0.5AU. The tail is seen visually for 30 degrees, extending to near Beta Centauri. This photo shows a fainter extension out to 38 degrees! The first 10 degrees of tail is still relatively bright, comparable to the norma starcloud.

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Mongo
post Dec 27 2011, 08:02 PM
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A spectacular image hosted on Gary Kronk's Cometography website. Photo taken by Gordon Garradd on December 22:

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Mongo
post Dec 29 2011, 02:00 AM
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Comet-ml post #19131 by Andrew Pearce:

QUOTE
Hi all

I finally observed this wonderful comet from a very dark sky site in northern Victoria (Lockington) Australia. The tail now extends almost to the Coalsack nebula. I measured it as 30.0 degrees on Dec 28.74UT. What is most striking about it is it's extreme straightness. For all the long tailed comets I've observed there always appears to be some degree of curvature but not so with C/2011W3. The surface brightness is fainter now and would be a struggle to see much in a light polluted area but it is very impressive from my current dark sky site. To the naked eye, the head of the comet is virtually non existent and I'm not sure there's a lot of value in a coma total magnitude estimate.

Regards
Andrew Pearce
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Mongo
post Dec 29 2011, 11:02 PM
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Comet-ml post #19142 by Andrew Pearce

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Hi All

The tail surface brightness is decreasing every day and as Rob mentioned, whilst it is visible with direct vision it is not easy. With averted vision however it is quite distinct. On Dec 29.73UT I measured the tail length as 32.0 degrees. It now extends almost to Alpha Crucis and can be faintly seen crossing the southern edge of the Coalsack nebula. It would be difficult to observe a longer tail than that visually as the line of the tail past Alpha Crucis extends into an area of the Milky Way which is very bright and the tail would be difficult to discern in this area and that will probably be the case over the next few mornings. The last 10 degrees or so of the tail is quite vague and ill defined in comparison to the first 20 degrees which is still quite narrow and very straight.

I'm leaving the dark country skies today so this will be my last observation but it's been a fascinating last week!

Regards
Andrew Pearce
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Mongo
post Dec 31 2011, 01:13 AM
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Comet-ml post #19150 by Chris:

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Hi all,
I observed this morning from 20kms East of Walcha, i also tried around 10:30pm on the evening of 30th Dec but moonlight washed out the tail in the background sky.

The tail was dimmer than SMC and slightly fainter than the Milky Way area just below the Pointers, i traced the tail to 22 degrees with the naked eye, which was just past Beta Cen, the eastern side of the tail end seemed to curve slightly to the East, the Western side appeared realtively straight.

There was a gap between the Milky way and the tail mid section which helped locate it with naked eye.

With 7x50 B's the head of the comet was 15' in dia, the width of the tail in the mid section was around 2 degrees, and fanned out to around 3.5 to 4 degrees at the end.

I did get a mag estimate but need to get to my program which is at work.

Cheers,
Chris W
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Mongo
post Dec 31 2011, 02:15 PM
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From comet-ml post #19154 by Michael Mattiazzo

QUOTE
The visual tail length with the unaided eye has reduced to 17 degrees, traceable to Alpha Circinus and photographically about 25 degrees. The bright milky way is interfering with the view.

The tail is continuing to fade with each passing morning and is now of similar surface brightness to the SMC.

Thus probably not observable from light polluted city skies.

Whether the reduced tail length is real or not, we will need to wait a few more days for the comet to move away from the milky way.
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Mongo
post Jan 1 2012, 06:39 PM
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Comet-ml post #19169 and #19174 by David Seargent

QUOTE
Hi All,

The tail has cleared the brightest part of the MW and this morning (Dec. 31. 1600 UT) I'm sure that I could trace it with averted vision into Carina; a length of (wait for it!) 45 degrees! The sky was very clear with a limiting naked-eye magnitude of around 6.5 or better.

Cheers,
David


QUOTE
Hi Rob and all,

Yes, I did put down a couple of wrong numbers (lack of sleep I guess). Still, it does not make a very great difference. The revised length comes out at 39 degrees ... and this time I checked the numbers! The end appeared to be near Theta Carinae, visible with averted vision only in "flashes". Perhaps it was averted imagination, but I think it was real.

Cheers,
David
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Mongo
post Jan 1 2012, 06:43 PM
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Comet-ml post #19176 by John Bortle:

QUOTE
By physical necessity and as I've pointed out previously, the dust tail of 2011 W3 SHOULD be continuing to lengthen...at least until the surface brightness of the outermost portions drop completely below the detection limits of the method being employed. For the unaided eye I'm afraid that this will occur fairly soon. However, for appropriately long exposed, highly processed, fairly small-scale images this interval should be considerably extended.

If astro-imagers familiar with the sorts of image processing done to bring out the absolute threshold details in such objects as galaxies apply their techniques to appropriate images of the comet I see no reason for the ultimate length of the tail not turning out to be something in the order of 50-60 degrees by mid January. I know that years ago when I dabbled in this area I could bring out details far beyond what I ever imagined were in the original images (although the pictures no longer were very pretty to look at!)

J.Bortle
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nprev
post Jan 2 2012, 03:28 AM
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Just heard from my stepdaughter, who returned today from a holiday hiking vacation in southern Chile. Although she's not an astronomy buff, she said that the tail very much resembled a searchlight beam a few days ago so it must have been quite spectacular. One of her fellow travelers apparently acquired a great shot, so hopefully I'll get a copy & be able to post it in a few days.


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Mr Valiant
post Jan 2 2012, 03:10 PM
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Arrgh, here I am, in South Western Australia, and Comet Lovejoy looks like it is going to be the comet I never saw. On the nights that may have delivered a good view of the comet, I have been at work, in a bright, 'night sky unfriendly' refinery, where only Jupiter and the brightest of stars dare peek through the glare. Days off, it's been cloud, or high level mist.
But team, I still remember my introduction to Comet Hyakutake. Myself and two mates, giving a home made, 8" f7 Newtonian its first light, in a dark, remote paddock. We knew the comet was coming; for the previous two nights, I'd spied 'it' (errm, do we regard comets as having the male or female vernacular?), with 50mm binoculars and saw a nice glowing blob, but no more.
This night, we spent our time, calibrating the telescope, checking out the local scenery, LMC, 47 Tuc, Jewel Box, Omega Cent, NGC 4945, Cent A (sorry guys), and by midnight, and after a few cans of light ale, it was time to head home. One last scan of the glorious vista, and I was the first to remark - 'whats that?'
I could see what appeared to be a distant search light in the north east.
"Ah, that's just the light (pollution) from the Alumina refinery (that is my place of work)", said my fellow. But after a minute, we knew, this was Hyakutake, so close, you could almost hear her (there ya go!). We stayed in the paddock 'till 3am, wishing we had a pair of 7X50's, though, through the telescope, the coma/nucleus appeared like a tiny point of light - the sun was due by 5:40.
I've just checked outside, high level cloud sad.gif
Many thanks to UMSF for this absorbing thread.
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Juramike
post Jan 3 2012, 02:11 AM
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Some nice images of Comet Lovejoy on Guillermo Abramson's flickr site:
http://www.flickr.com/photos/12759894@N06/6623516639


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Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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Mongo
post Jan 3 2012, 01:48 PM
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Comet-ml post #19187 by David Seargent

QUOTE
Hi all.

Yesterday morning ((Jan. 1 UT) the sky was clear though possibly not quite as transparent as previous morning, but the tail appeared very faint (only clear with averted vision) and could be traced for "only" 26 degrees. But this morning (Jan 2 UT), conditions appeared worse, with lots of high cloud and the head hidden behind a thick patch of cloud. Yet, remarkably, the tail was much clearer, obvious (albeit faint) with direct vision and traced for some 42 degrees - until lost in the Milky Way near the border of Vela. And this time I double checked the figures and tripple checked the calculation!

Cheers,
David
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Mongo
post Jan 3 2012, 01:50 PM
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Comet-ml post #19188 by David Seargent

QUOTE
Hi all,

Just a few ideas to put before the group.

As I wrote previously, I suspect that the initial intrinsic faintness of this comet was not so much a function of the small size of the nucleus, but of the presence of a surface crust of refractory material. If the nucleus was about 500 metres diameter (as against the 100 - 200 as initially estimated) and covered by an insulating crust, this might explain how it survived perihelion passage intact. If the insulating layer was blown off around perihelion, this may even have formed a "sun umbrella" of particles that shielded the freshly-exposed icy surface of the nucleus, rather as is thought to have happened to Seki-Lines in 1962 (analysis of the dust tail suggests that this comet shut down for a few hours at perihelion - q = 0.03 AU - which also helps to explain why there were no daylight sightings of this intrinsically bright object). In the case of Lovejoy, a similar event may have been a factor in preserving its existence. Once the meteoric cloud dispersed, the comet burst into furious activity, however by then the worst of its ordeal was already over.

The presence of an ion tail clearly indicated an active nucleus following perihelion. However, as this has this has now disappeared, it may be that ice-driven activity has ceased. This could mean that the nucleus has disappeared, or run out of ice or (I think the most likely explanation) has had the ice cooked out of the surface layers. In other words, the comet may by now have built up a new insulating layer that is effectively keeping heat from underlying ice.

Yet, the "head" appears to be persisting as if some dust continues to be released. Just a speculative thought, but electrostatic repulsion caused by solar radiation can levitate fine dust on the surface of the Moon (causing the unexpected crepuscular rays seen by the Apollo astronauts) and is thought responsible for the small flare experienced by Phaethon in 2009. With respect to the latter, David Jewitt called Phaethon a "rock comet" - capable of low-level activity even in the absence of ice - and suggested that this process may even be responsible for the formation of the Geminid meteor stream. For what it is worth, I suggest that the present weak activity of Lovejoy could be due to this process lifting dust from what has again become a totally encrusted nucleus.

All very speculative I know, but comments welcome.

Cheers,
David
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Mongo
post Jan 3 2012, 11:13 PM
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Comet-ml post #19197 by John Bortle:

QUOTE
David - As a first approximation, I would say that your conclusions seem quite reasonable. Certainly, something quite unusual occurred with Comet Lovejoy over the course of its apparition. That its post-T survival, at least to a degree, violates my perihelion survival "law" is most interesting, although I would note (as my paper on the subject indicated) that a number of small, periodic comets (like P/Encke, et al.) do so on a quite regular basis. The situation being so, this suggests to me that Comet Lovejoy must have experienced at least one previous perihelion passage as a totally independent body (i.e. it was not a fragment formed a its immediate previous perihelion passage) and thus had a fully formed and fairly dense overall insulating layer over its entire surface.Such a "baked" surface which totally shuts down early might well also explain why Kreutz sungrazers tend to disappear much sooner post-T (typical by about 1.5 AU post-T) than do other comets of similar intrinsic brightness.

There is also the problem that although of a seemingly extremely faint intrinsic brightness both pre and post-T, Comet Lovejoy still presented a viable and distinct "head" post-perihelion. This while objects like the Great Southern Comet of 1887, assumed to be much brighter intrinsically than 2011 W3, appeared to have survived only as huge tail apparently without any head. Of course, the Kreutz sungrazing group's orbital orientation so strongly favors visibility from the Southern Hemisphere that it has undoubtedly limited the opportunities to watch the development of other examples of seemingly faint members of this clan in the more distant past.

I find it equally interesting how one explains the long-enduring bright streak extending from the position the nucleus should occupy to relatively far out into the tail. And the fact that this feature seems to have evolved surprisingly little since its sudden appearance. A few descriptions of the Great September Comet of 1882 do make mention of a similar "streak" in that comet's head, dotted with a number of brighter star-like nucleii, but that feature seemed fairly short lived and was on a physical scale apparently far smaller than that displayed by Comet Lovejoy. Are we perhaps seeing a very long train of tens of thousand of ONLY tiny fragments with absolutely no large survivers, distributed along the orbit by size/mass? But then how could this form so suddenly and how could a coma persist without some viable solid body evident at its focus? According to Rod, there is no evidence of any independent surviving body down to 19th magnitude in that location.

And I'm still very curious about the nature of the faint yet distinct "sheath" that is seen to envelope both the dust and gas tails of numerous Kreutz sungrazers post-T, well seen with 2011 W3, yet does not seem evident with regard to other very small "q" non-Kreutz comets. What is the nature of it? And in the case of the Great September Comet it not only surrounded the tail but was described to extend well sunward of the head!

I unquestionably foresee a long and interesting future of papers attempting to address the amazing sights we've seen over the course of the past month!

J.Bortle
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