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The Great Christmas Comet of 2011, 2011 W3 (Lovejoy)
Mongo
post Dec 22 2011, 10:53 PM
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Here is a cropped version of the full-resolution photo of the comet from the ISS:

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Mongo
post Dec 22 2011, 10:58 PM
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I like this shot, taken by Jim Gifford, it is very atmospheric:

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Mongo
post Dec 23 2011, 12:35 AM
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From comet-ml post #19031 by David Seargent:

QUOTE
Hi all,

At last, a clear morning here at Cowra. And the comet was glorious! tail was measured at 15 degrees, with the furthest portion dividing into a split main tail and a secondary emerging from the curving main one, giving the effect of a spreading triple tail. The main tail was judged to be about three quarters of a degree in width.

By contrast, the coma was very inconspicuous. In the 25x100 binocular telescope, a very rough estimate gave just mag. 5. However, saying that the comet was fifth magnitude gives absolutely no impression of the spectacle! The head was simply lost against the intense tail.

I had the strong impression that the central portion (in terms of length) of the tail was the brightest. The extremity was (not surprisingly) fainter, but the section closest the head was (more surprisingly!) fainter as well. At first, I thought that this was just the effect of lower elevation, however the impression continued as the comet rose higher, so I now think that it was at least partially real (although elevation no doubt contributed to some degree.) I recall that the same was true of Ikeya-Seki. In that instance, the brighter section was crossed by stria, however, I saw no evidence of stria in W3. Interestingly, with the naked eye, the tail seemed to wax and wane in intensity; an effect also noted in Ikeya-Seki. No doubt, this is simply due to waves in our atmosphere, but it nevertheless added to the spectacle.

There is no doubt that this comet is included amongst the Great Comets of history. Not the "greatest of the Greats" like Ikeya-Seki, Hyakutake, Hale-Bopp and McNaught, but certainly high on the list of the runners up!

Once more, congratulations Terry on this historic find. Your skill and dedication has been well rewarded!

David
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Mongo
post Dec 23 2011, 01:57 AM
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A great photo by Lester Barnes of south Australia:

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Mongo
post Dec 23 2011, 01:29 PM
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Commentary by John Bortle (comet-ml post #19037) on the photo just above this post, by Lester Barnes:

QUOTE
I am particularly taken by this latest image in that it almost precisely replicates images of Comet Ikeya-Seki from 1965. The match is nearly exact, right down to the distinctly brighter tail edges, the twists in the tail and even the faint outer sheath enveloping the bright dust tail. Such a feature was also seen in some of the drawings of the Great September Comet of 1882. Truly, Kreutz sungrazers are a group of comets absolutely unique unto themselves!

There seems to be some panic arising among folks currently experiencing cloudy skies down under, thinking that they may miss the whole show. Fear not, for as I pointed out previously although the comet's head will continue to fade rapidly, the tail will drop in brightness far more slowly. If it should follow the evolution of the tail of Ikeya-Seki, then the outer-most portion of the long dust tail will hardly fade at all over the next couple of weeks. However, the tail's middle section will, until it has faded to match the end portion. Then the entire tail will seem to fade as a unit. Remember too, that the tail will be continuing to grow throughout the period. I would anticipate the it might attain a final naked eye length of ~25 degrees, by which time it will be very faint and difficult ghostly specter to the naked eye.

I was interested to hear that David S. reports variations in the brightness of the tail over the course of a short time, a phenomenon referred to a coruscation. Such has been reported on rare occasions throughout cometary history. Although usually attributed to atmospheric instability, some instances have been much harder to explain as such and if seen, it should always be recorded, along with details of the prevailing weather conditions.

J. Bortle
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Mongo
post Dec 23 2011, 01:34 PM
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From comet-ml post #19038, replying to David Seargent's post:

QUOTE
I've been wondering when comet Lovejoy would earn the title Great comet and between your description and Lester's image, and all other images and reports from observers around the southern hemisphere, there is no question about it. The Great comet of 2011 it is.

Comet Lovejoy being a Great comet does imply another (very) impressive fact: just about any Kreutz sungrazer that does survive perihelion, even a small one, has the potential to become a Great comet. It only depends on the timing. So with a bit more luck then, both comet Pereyra and White-Ortiz-Boleli could have become Great comets.
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Mongo
post Dec 23 2011, 01:42 PM
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Another report on the comet by Geoff Dudley (comet-ml post #19039):

QUOTE
I went to The Briars (Mornington Peninsula AS HQ) down at Mt Martha yesterday morning 22Dec11, got there around 0340.

Greeting me were Rod Brackenridge and Greg Walton. Greg had setup 3 binocular chairs, an 8" SCT and 3 SLR cameras. I arrived prior to the comet rising so a very pleasant and comfortable time was had by all just generally admiring the sky, (which was beautiful and clear almost to the SE horizon)with 10 x 80's when at 0410 Greg said, "Someone's got a searchlight on over towards Hastings". He was right except for the fact that the beam was curved slightly northwards. I'd never heard of a curved searchlight beam and it wasn't moving about so it was then that we realised that it was the comet. It was easily visible, we didn't need binos. I stuck my hand out at arm's length and found that it just covered the comet so I guess the length was about 15-20 deg. We couldn't see a head, it may have been too low in the atmosphere. I had a look for comparison stars and took a punt on it being around mag 2 or 3. Very hard to work out with accuracy as the Sun was rising. The comet stayed visible even thru astronomical twilight.

Finally at 0444 we lost it.

Greg took lots of photos as his cameras were set to auto expose for around 10 secs each. He got a nice shot of the tail with a 120mm lens and when zoomed in clearly showed the split. It was a WOW moment.

Merry Xmas to all!

-- Geoff Dudley


One of the photos mentioned above:

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Mongo
post Dec 23 2011, 02:00 PM
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Now that Lovejoy is "officially" a Great Comet, I have decided to update the ranking of the Great Comets of the past several centuries that I had done here at the time of comet McNaught in 2007.

The point scale went like this:

QUOTE
MAGNITUDE: 10 points for every degree of magnitude brighter than +3 (dark-sky; daytime magnitude gets counted separately)


No points in this category.

QUOTE
TAIL: 1 point for every two degrees of length of naked-eye visible tail in dark sky

DURATION VISIBLE: 1 point for every month naked-eye visible in dark sky


The last confirmed report I read gave a tail length of about 28 degrees, for 14 points. I also assume the minimum duration of visibility of one month, for one additional point.

QUOTE
BONUS POINTS:
2 visible tails = 10 points
5 visible tails (West 1976) = 20 points
15 degree long anti-tail (Arend-Roland 1957) = 10 points
curved tail (Donati 1858) = 5 points
'bright' tail (Daylight 1910) = 10 points
'brilliant' tail (Ikeya-Seki 1965, Great September 1882) = 20 points
circumpolar all night (Hyakutake 1996, Tebbutt 1861) = 10 points
Mag. -3 in daylight (West 1976) or Mag. -5 in daylight (Daylight 1910) = 10 points
Mag. -8 in daylight (Great March 1843) = 15 points
Mag. -15 in daylight (Ikeya-Seki 1965) or Mag. -17 in daylight (Great September 1882) = 30 points


While currently fading, the tail was considered bright earlier, for 10 points, and it will be circumpolar all night after New Years Day, for another 10 points. It also reached about magnitude -4 when rounding the sun, for 10 additional points. There were definitely two visible tails, a dust dail and an ion tail, for 10 points. While its tail is curved, it was not curved strongly enough to gain more points. This may change as the viewing geometry changes.

Using these numbers, comet Lovejoy currently garners 55 points.

The updated list:

1861 123 pts Tebbutt
2007 105 pts McNaught
1882 101 pts Great September Comet
1910 95 pts P/Halley
1976 90 pts West
1996 78 pts Hyakutake
1997 73 pts Hale-Bopp
1858 68 pts Donati
1965 64 pts Ikeya-Seki
1970 61 pts Bennett
1957 57 pts Arend-Roland
2011 55 pts Lovejoy
1910 54 pts Daylight Comet
1811 52 pts Great Comet
1927 51 pts Skjellerup-Maristany
1843 50 pts Great March Comet
1874 46 pts Coggia
1881 42 pts Great Comet
1807 37 pts Great Comet
1853 37 pts Klinkerfues
1835 35 pts P/Halley
1957 35 pts Mrkos
1860 31 pts Great Comet
1911 29 pts Beljawsky
1911 28 pts Brooks
1819 25 pts Tralles
1854 24 pts Great Comet

Here is the same list in reverse chronological order:

2011 55 pts Lovejoy
2007 105 pts McNaught
1997 73 pts Hale-Bopp
1996 78 pts Hyakutake
1976 90 pts West
1970 61 pts Bennett
1965 64 pts Ikeya-Seki
1957 57 pts Arend-Roland
1957 35 pts Mrkos
1927 51 pts Skjellerup-Maristany
1911 29 pts Beljawsky
1911 28 pts Brooks
1910 95 pts P/Halley
1910 54 pts Daylight Comet
1882 101 pts Great September Comet
1881 42 pts Great Comet
1874 46 pts Coggia
1861 123 pts Tebbutt
1860 31 pts Great Comet
1858 68 pts Donati
1854 24 pts Great Comet
1853 37 pts Klinkerfues
1843 50 pts Great March Comet
1835 35 pts P/Halley
1819 25 pts Tralles
1811 52 pts Great Comet
1807 37 pts Great Comet
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Mongo
post Dec 23 2011, 07:04 PM
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As expected, comet Lovejoy is growing more prominent as the New Moon approaches, and as the comet itself gets nearer. From Vello Tabur in comet-ml post #19044:

QUOTE
Finally, I didn't have to drive too far this morning - only 30 mins out of Canberra to an old comet hunting location. My son and I arrived at 3 am and were immediately treated to a glorious sight upon stepping out of the car, with 2/3 of the tail already above the horizon. The comet seems brighter again, now that it is visible in a dark sky without moonlight interference. The brightest part (about 1/3 of the way along the tail from the head) easily outshines the LMC.

Got a few nice snaps too but I've only had time to put up this one:

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Mongo
post Dec 23 2011, 07:15 PM
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To make comparisons easier, I have put images of Ikeya-Seko (left) and Lovejoy (right) together. Lovejoy is clearly not as bright as Ikeya-Seki, but otherwise seems quite similar.

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Mongo
post Dec 23 2011, 07:21 PM
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The tail is getting bigger! From Rob Kaufman in comet-ml post #19045:

QUOTE
First clear morning here, and I was gobsmacked! It is huge, not quite McNaught scale but huge. I never saw the head rise because I have high hills around but I saw approximately 20-deg of tail emerge before it was finally washed out, first visually and then photographically.

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Mongo
post Dec 23 2011, 10:42 PM
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From Robert McNaught, comet-ml post #19047:

QUOTE
Despite a huge downpour of rain around midday, the humidity after midnight was sufficiently low that once the cloud passed, there was no fog or significant orographic cloud.

My initial impression as the comet was rising was that it was less bright than on Dec 21, leaving me a little disappointed. However once the full extent of the comet was visible, it continues to be awesome! Unlike Vello, I do suspect an overall fading, although it did appear to be a bit higher surface brightness than the LMC.

A scan with 10x50B really didn't show much structure, although the gas tail was more evident in the binoculars than to the naked eye. In 20x120B there is no sign of any condensation. Instead a little "spine" is evident (more on this later). The overall tail length from the photos is 21.7 deg for the dust tail and much the same for the dust. Averted imagination could make it longer, but I think lines of stars are being misleading.


QUOTE
So just what is happening at the heart of the comet? My interpretation, which I fully admit is from a position of ignorance, would be that there is an intact nucleus. This is based on the "spine" coming to a sharp point close to the the parabolic hood. If it were dissipating I would have expected the spine to be more diffused and for the parabolic hood to diffuse with it. There will be plenty of folks here that interpret the situation more reliably than me, but it certainly doesn't seem to be a Shetland comet ;-) (that's a Scottish joke).

Until tomorrow night.

Cheers, Rob


He also linked to several outstanding photos that he had taken:



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Mongo
post Dec 23 2011, 11:08 PM
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More confirmation of today's observations, by Chris W in comet-ml post #19050:

QUOTE
Hi all,

This morning i had to travel to a roadside spot between Nemingha and Loomberah (near Tamworth NSW) to view the comet. I arrived there at 3:50am AEDST only to find over half the comet has already risen!

At 4:20am AEDST i observed the comet's tail to be 22 degrees in length, the tail tip about 2 to 3 degrees in width and comparable in brightness to the Small Magellanic Cloud, the mid section between the head and "tail-split" about half a degree in width and comparable in brightness of the bar in the Large Magellanic Cloud. The comet head had no central condensation visible through 7x50 B's. The overall brightness of the comet appeared fainter than my previous observation 2 mornings earlier, the tail split was not as noticeable and the ion tail was hardly discernable.
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Mongo
post Dec 24 2011, 03:53 AM
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A response by Vello Tabur in comet-ml post #19055 to Rob McNaught's post #19047, two posts above this one:

QUOTE
Hi Rob,

It's quite possible that the comet has faded somewhat. My comments were relative to a reference point of two nights ago (Dec 21.7 UT), when there was still moonlight interference. I didn't see it the following night due to fatigue (I needed some sleep after racking up nearly 1000 km in the last few days). The view last night (Dec 23.7) finally had the comet reasonably high in a dark sky. Relative to 2 nights before, it was significantly easier to see with the naked eye and far more impressive. To my eye, it had transformed from a ghostly spectre to something of real substance. Having said that, I agree that the ion tail was less obvious and less structure was visible in the tail through binoculars. Overall -- still awesome!

Cheers,
Vello
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elakdawalla
post Dec 24 2011, 04:03 PM
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Mongo, I just want to say thanks for these summaries -- it's great to have a single, concise source for the latest comet visibility news! Though it's making me very jealous of our southern hemisphere friends.


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