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Unmanned Spaceflight.com _ Sun _ The Great Christmas Comet of 2011
Posted by: Sunspot Dec 2 2011, 09:59 PM
http://sungrazer.nrl.navy.mil/index.php?p=news/birthday_comet
Possible very bright sungrazing comet coming mid December - Comet Lovejoy C/2011 W3 (Lovejoy)
Information in the link above.
Posted by: Sunspot Dec 14 2011, 09:22 AM
Here it comes
http://sohowww.nascom.nasa.gov//data/REPROCESSING/Completed/2011/c3/20111214/20111214_0830_c3_512.jpg
Posted by: titanicrivers Dec 15 2011, 04:14 AM
And check out the SOHO Movie Theater! Choose LASCO C3 and the latest 20 or so images.
http://sohodata.nascom.nasa.gov/cgi-bin/soho_movie_theater
Posted by: Mongo Dec 15 2011, 07:59 PM
http://spaceweather.com/
COMET LOVEJOY UPDATE: Matthew Knight of the Lowell Observatory and JHU-APL reports: "As of 16:30 UT on Dec. 15th, Comet Lovejoy has reached magnitude -3, possibly brighter. It is starting to saturate SOHO images even with narrow filters and shorter than normal exposure times." The comet is now brighter than Jupiter, but not quite as bright as Venus. If these developments continue apace, Comet Lovejoy could become visible to the naked eye in broad daylight before the end of Dec. 15th.
Posted by: stevesliva Dec 15 2011, 08:05 PM
NFW. I'll have to squint through some clouds.
Posted by: Mongo Dec 15 2011, 08:31 PM
Same here. Right now it's overcast from horizon to horizon where I am. 
Posted by: Juramike Dec 16 2011, 02:06 AM
It lives!
http://www.youtube.com/watch?feature=player_embedded&v=LBJ2mkI1rSc
Posted by: Mongo Dec 16 2011, 03:52 AM
Here is another video:
http://sdoisgo.blogspot.com/2011/12/phoenix-comet-emerges.html
I should add that the comet may look faint in these videos, but the cameras are optimized to stare at the surface of the sun. The fact that the comet is visible at all indicates its tremendous brightness.
Posted by: Explorer1 Dec 16 2011, 08:09 AM
That's one tough cookie....
Any estimate for how close it got (in terms of solar radii)?
Posted by: jamescanvin Dec 16 2011, 08:31 AM
140,000 km (1.2 solar radii) above the surface
Posted by: Sunspot Dec 16 2011, 09:48 AM
Seems to have left it's tail behind. 
http://lasco-www.nrl.navy.mil/javagif/gifs/20111216_0930_c3.gif
Posted by: Mongo Dec 16 2011, 02:45 PM
Actually, the radius of the Sun is 695,500 km, so Comet Lovejoy approached to 0.2 solar radii above the photosphere.
Posted by: Toma B Dec 16 2011, 04:08 PM
That tail was so OUT it's growing itself new HOT tail.
http://lasco-www.nrl.navy.mil/javagif/gifs/20111216_1530_c3.gif
Posted by: Mongo Dec 16 2011, 10:12 PM
It is still very soon, but it appears that Comet Lovejoy is actually brighter than it was at the same distance from the Sun on the way in, and continues to brighten. (This is not a total surprise -- historically, close sun-grazers have tended to be more spectacular after perihelion than before, provided they survive it.) It could end up being a brilliant comet in the southern hemisphere in the coming days, once it moves a bit further from the Sun's glare.
http://f1.grp.yahoofs.com/v1/YL_rTj6fDURUtA_CRotjEIMh2ou1BpEQgOFd8hhiAp2njG6NjneAaMLePeCYaLCz-TBMQvj2R01ubkekS4a94N8_RQsVSpCKXEPXCQC3_g/lovejoyC3near16.mov
(The nucleus's brightness can be very crudely estimated from the size of the white oversaturation bars extending from the nucleus. They are already longer than any seen by this camera on the inbound trajectory.)
Posted by: Sunspot Dec 16 2011, 10:47 PM
The Ion tail has reappeared too.
Posted by: Mongo Dec 17 2011, 03:29 AM
Another movie:
http://sohowww.nascom.nasa.gov/data/LATEST/current_c3.gif
This site only shows the last 3 days of observation, so it's fine for the next day or so, but after that it will be less useful. But right now, it's spectacular!
Posted by: nprev Dec 17 2011, 03:34 AM
The next few days may prove interesting...and spectacular for those south of the Equator.
Posted by: SteveM Dec 17 2011, 03:39 AM
http://sohodata.nascom.nasa.gov/cgi-bin/soho_movie_theater
Posted by: Sunspot Dec 17 2011, 01:10 PM
Visual sightings starting to come in now.
Posted by: Floyd Dec 17 2011, 02:31 PM
Why is the view better from south of the Equater? Unless you are above the artic circle...if you can see the sun, you can see the comet?
Posted by: Mongo Dec 17 2011, 02:58 PM
Comet Lovejoy is no longer a daylight comet, so darkish skies are needed to see it with the unaided eye.
Basically, the orbit of this comet appears from Earth at about a 45 degree angle from the ecliptic towards the south. This means that at mid-southern latitudes, the orbit takes the comet almost directly 'above' the sun at sunrise, so that it will be visible (in the coming weeks) well before sunrise, in fairly dark skies. Therefore the contrast of the comet against the sky will be very good, and its tail will be quite visible (and indications are that the tail will become quite lengthy in the coming weeks).
On the other hand, at mid-northern latitudes the comet will be moving away from the sun in a direction almost parallel with the horizon at sunrise, so it will not even appear above the horizon until the sun is nearly rising (and turning the sky very bright), and remain lost in the near-horizon haze until full daylight. The contrast of the comet against the sky will be far worse than from the mid-southern latitudes, and it is likely that it will not even be visible to the naked eye at all, unlike the situation from the mid-southern latitudes where it is expected to be quite prominent in the pre-sunrise sky.
So we have had two Great Comets in a row (McNaught and now with any luck Lovejoy) best seen from the mid-southern latitudes, and poorly visible from the mid-northern hemisphere. Oh well, those are the breaks.
Posted by: Floyd Dec 17 2011, 06:00 PM
Thanks Mongo, great explanation!
Posted by: MaG Dec 17 2011, 08:46 PM
Our friends took image from Argentina today morning. 
http://www.kommet.cz/
And here's my imagination of comet's path in LASCO C3..
What an exciting weekend.
Posted by: Mongo Dec 18 2011, 10:30 PM
This was posted today by highly respected astronomer John Bortle on the comets-ml mailing list:
The tails of some of the major sungrazing comets have been extraordinarily bright. So much so, in fact, that even their exact terminus, usually a vague and extremely ill-defined feature for more typical bright comets, can be clearly evident to the unaided eye. In the case of the Great March Comet of 1843, the Great September Comet of 1882 and 1965's Comet Ikeya-Seki, the tails appeared rather like segments of a bright searchlight beam, so high in their surface brightness that their total length was distinctly obvious to most observers.
Comet Lovejoy's apparition has been so bizarre up to this point that it is truly difficult to anticipate just what might happen next. Even more hazardous would be to attempt to accurately predict the exact sort of tail it will unfurl in the morning sky. However...in my opinion the potential is there for something quite unusual, perhaps even extraordinary, to present itself, particularly by virtue of the current geometry between the comet and Earth, as it presents the most favorable circumstances possible for observing the tail of a Kreutz sungrazing group comet.
I personally await with great anticipation the first reports of Comet Lovejoy's tail as the comet exits the twilight and begins to traverse the morning skies of the Southern Hemisphere. Please...be complete, accurate and as detailed as possible in describing what you see, the coming event may prove historic.
J.Bortle
Posted by: nprev Dec 18 2011, 10:34 PM
...if John Bortle says anything about comets, I believe it.
Those are some strong words. Wow.
Posted by: Stu Dec 18 2011, 10:48 PM
Wow.
Ok, now I really am officially northern hemisphere hacked off. First McNaught dazzles southern hemisphere observers only, now Lovejoy...
Posted by: nprev Dec 18 2011, 10:55 PM
Now, now, Stu...we had Hale-Bopp! 
But, yeah, I feel some hemispherical comet-envy myself here. If I had the money & time my butt would be on the next flight to the most southerly location with good weather predicitions possible.
Posted by: scalbers Dec 18 2011, 11:33 PM
Ok, now I really am officially northern hemisphere hacked off. First McNaught dazzles southern hemisphere observers only, now Lovejoy...
Just for the record, there were things of interest to observe with McNaught from 40N latitude. Just around perihelion time, it actually was to the NE of the sun and best visible from northern latitudes at mag -5 to -6. I saw it in broad daylight in binoculars, and naked eye just after sunset. Furthermore, the ghostly outer rays of the tail were pointing straight up from the western horizon after evening twilight ended a few days later.
Now with Lovejoy, it was spotted in broad daylight from France - of course a mid-northern latitude - image can be seen at this link:
http://spaceweather.com/submissions/large_image_popup.php?image_name=Vincent-JACQUES-f-ff-fff_msq_1324194382.jpg
Really would be interesting to plot this comet's magnitude vs solar elongation in comparison to McNaught and Ikeya-Seki.
Steve
Posted by: Mongo Dec 19 2011, 12:21 AM
Report of a daylight sighting of Comet Lovejoy on comets-ml mailing list:
by Rick Baldridge
The amazing happened. Comet Lovejoy (C/2011 W3) survived what was thought to be a suicide plunge into the solar corona, passing only 78,800 miles from the surface of the Sun on December 16th – not quite 1/10th a solar diameter! Surprisingly, the comet reappeared on SOHO LASCO images barely 1 hour after perihelion passage, prompting Brian Day of NASA/Ames and I to attempt a daylight observation.
We ran up to Foothill College Observatory (Los Altos Hills, CA) at lunch time on Dec 16th and opened up the dome. I quickly made a 3" aperture off-axis mask for the Meade 16" Schmidt scope, which allowed me to use the dome shutter as a glare shield, keeping direct sunlight out of the telescope tube assembly. Comet Lovejoy was barely 4° west of the sun during the attempted observation.
Finding Venus first to focus on, I used coordinates from JPL HORIZONS to center the `scope on the comet's expected position. After looking through a 127x eyepiece for a few moments – THERE IT WAS! A very star-like nucleus with a faint but obvious fan shaped glow streaming away from it. The fan was maybe 20 arc-seconds long. A very rough guess was the nucleus was magnitude -1, based on my impression of the appearance of Mercury years ago at a similar solar elongation. This initial sighting came at 11:48am PST (Dec 16th at 19:48UT)
Brian Day was quickly called, who had just driven into the Observatory parking lot. He came up, took one look in the eyepiece, and after adapting to the brightness of the background sky, exclaimed, "DAMN! There it is!"
We were ecstatic! Seeing a daylight comet is an extremely rare thing, and so close to the sun – only 4 degrees. Truly amazing!
Unfortunately, Brian and I did not have our DSLRs to attempt taking a photo. We tried our cell phone cameras, holding the lens up to the eyepiece using afocal projection, but to no avail.
It was an experience we will never forget!
Posted by: nprev Dec 19 2011, 12:58 AM
Wow.
Mongo, please keep feeding salient info like this at your discretion. I think that there is a SLIGHT chance that this thing might be visible to unskilled observers over the next few days, and anything we can do to promulgate awareness would be very useful. Thanks!!!
Posted by: Mongo Dec 19 2011, 02:15 AM
For those readers who are in the southern hemisphere, here is a finder chart for Comet Lovejoy from latitude 35 degrees south, for this Tuesday morning before sunrise:
http://nightskyonline.info/wp-content/uploads/2011/12/2011_W3_finder_chart_Tuesday_20_December_2011_daylight1.png
This is from http://nightskyonline.info/?p=2836
Posted by: Mongo Dec 19 2011, 02:14 PM
From Malargue, Argentina this morning:
http://img.photobucket.com/albums/v455/mongo62aa/tail.jpg
Posted by: Mongo Dec 19 2011, 08:44 PM
Finder chart for 35 degrees south on Wednesday morning:
http://nightskyonline.info/wp-content/uploads/2011/12/2011_W3_finder_chart_Wednesday_21_December_2011_daylight.png
Posted by: Stu Dec 19 2011, 09:30 PM
Tail sighted - and photographed - from Australia...
http://www.spaceweather.com
Posted by: Mongo Dec 19 2011, 09:45 PM
This is interesting. From the comet-ml mailing list:
Some faint "outer tail" is now visible and there is something new, which looks like a ray in tail from nucleus looks like a synchrone.
http://img.photobucket.com/albums/v455/mongo62aa/average_v1219_1.png
Posted by: nprev Dec 20 2011, 04:06 AM
Magnificent!!!
Posted by: machi Dec 20 2011, 10:06 AM
Amazing images, it's unbelievable, that this little comet survived flyby so close to Sun!
Posted by: tasp Dec 20 2011, 02:06 PM
Impressive it withstood the tidal effects too.
Posted by: Mongo Dec 20 2011, 06:59 PM
Latest today from comet-ml mailing list:
I observed Lovejoy this morning from Woolbrook, NSW, i am so excited, at 4am AEDST i took an image of the Eastern horizon and upon looking at the image i noticed a thin "search beam" like extension pointing up from the SE, tilted a little to the North. I looked with my naked eye and saw what appeared to be headlights of a car near my horizon but it didn't seems to move, long story short....the tail i measured over the next 50 mins was nearly 15 degrees long and in moonlight!
Clouds not long intervened at dawn and i tried for the comet head but saw nothing in my 10" dob.
Images to follow!
Cheers,
Chris Wyatt
Walcha, NSW
Australia
The comet, as expected, is getting more prominent as it starts to move out of the morning twilight.
The thread title is "The SOHO Birthday Comet", but I think a better name would be "The Great Christmas Comet of 2011", since with the new moon on December 24th, viewing conditions should greatly improve just in time for Christmas. Not to mention that by then it should be well clear of the morning twilight, and significantly closer to Earth with a better viewing geometry.
Posted by: nprev Dec 20 2011, 07:45 PM
In moonlight, no less.
Good grief.
Posted by: Mongo Dec 20 2011, 08:40 PM
Finder charts for 35 degrees South latitude on Thursday morning:
http://nightskyonline.info/wp-content/uploads/2011/12/2011_W3_finder_chart_Thursday_22_December_2011_daylight.png
Posted by: jamescanvin Dec 20 2011, 09:45 PM
I agree, I added the "2011 W3 (Lovejoy)" subheading earlier today to help identify the thread and have now changed the main title to your suggestion.
Posted by: Mongo Dec 20 2011, 11:51 PM
Oh-oh. That title change may have been premature. It appears that the comet nucleus may have broken up within the past few hours.
From comet-ml post #18949:
Filtered images from FRAM this morning (average of best pictures).
http://www.kommet.cz/datas/users/1220average_r_dbe_1.png
http://www.kommet.cz/datas/users/1220average_v_dbe_1.png
From comet-ml post #18950 by Gary Kronk:
From comet-ml post #18952:
http://sungrazer.nrl.navy.mil/index.php?p=images/lovejoy/lovejoy_hi1a_srem_dec18\_19.gif
Where would all the new dust be coming from? There rate of new dust tail extension is occurring rapidly. Possible breakup starting?
From comet-ml post # 18955 by Gary Kronk:
http://cometography.com/lcomets/1999s4.html
If you scroll down a bit, you will see two pictures from 1999 July 21, that show a bright tail ray. Within days the comet was unmistakably breaking up.
By the way the link to my comet Lovejoy web page is as follows:
http://cometography.com/lcomets/2011W3.html
Sincerely,
Gary
Posted by: Mongo Dec 21 2011, 12:27 AM
A photo from http://www.iceinspace.com.au/forum/showpost.php?p=800218&postcount=98:
http://img.photobucket.com/albums/v455/mongo62aa/CometLovejoy21-12-2011WA.jpg
Posted by: Mongo Dec 21 2011, 12:52 AM
From comet-ml post #18958:
When I first looked out this morning (from Cowra in central NSW) and saw the layers of high and middle-level cloud, I almost went back to bed. But after a few minutes deciding, I set up the 25x100 binocular telescope and started to sweep along the horizon which, surprisingly, was clear for the first two or three degrees. At 4.20 local summer time (1720 UT) I noticed something like a distant searchlight beam rising over the slope of a small hill which sports the rather grandiose name of "Porter's Mount". With the sky becoming bright, I could see a clear feature on the local horizon (a tree about two thirds of the way up the grassland slope of Porter's Mount) near where the beam emerged and, finding this without the telescope, I could then see about 2 - 3 degrees of tail rising up to a bank of heavy cloud. The tail must have been quite intense to be seen in such a bright sky and, from the calculated position of the head, at least 7 - 8 degrees long (although most of this was not seen. Neither was the head as the sky had become very bright by the time it would have cleared Porter's Mount).
On a slightly different topic, as one of the few Ikeya-Seki veterans in this group, it is probably timely to sound a warning not to give up on this comet because of the degree of fading that has obviously taken place. Back in 1965, the arrival of I-S at perihelion was surrounded by a lot of media hype. Predictions that a comet brighter than the Moon was coming, while they turned out to be technically true, failed to make clear that the comet would be only a few arcminutes from the Sun's limb at that time and would fade very rapidly afterwards. Of course, the general public missed much of the display at perihelion and dismissed the comet as a dud. On the day of perihelion, Fred Whipple called it "a scientist's comet"; one that was great for astronomers but a disappointment for the public. Unfortunately, the media dropped the subject (by and large) and when the "public" show occurred over a week later, only those who normally rose before dawn for work or other purposes saw it.
My first couple of views post perihelion were not all that exciting. High cloud always seemed to shroud the eastern horizon and by the time the comet cleared this, the sky was very bright and the comet looked washed out with only a small diffuse spot of a coma and a fading tail. Then, exactly 10 days after perihelion, there was a morning of exceptional clarity and by that time the comet was far enough from the Sun to be rising in a dark sky. The sight was magnificent. In the dark sky, the coma appeared brighter than the earlier twilight views and looked small and dense. As for the tail, this appeared (as John Bortle has written on several occasions to this group) "solid", not diaphanous like the tail of a normal comet. And there was little "normal" about Ikeya-Seki! Today, we would probably think of laser beams or Star-Wars light sabres ... but this was back in 1965!!
Now, I am certainly not saying that W3 will become as remotely spectacular as I-S, but the lessons of 1965 are worth noting. The comet may become faint, but the tail may well retain relatively high surface brightness for quite some time and be impressive in coming days as it pulls out from the twilight (and moonlight). Don't dismiss this comet just yet! There may still be surprises in store.
David
In response to this, John Bortle wrote in comet-ml post #18961:
Go back and consult some of my earlier posts concerning the development of Comet Ikeya-Seki's post-T dust tail. Such may well foreshadow the sort of evolutionary path that the tail of Comet Lovejoy may see in days to come on a somewhat more modest scale.
Folks, be assured that the show isn't over yet by any means.
J.Bortle
Posted by: Mongo Dec 21 2011, 05:06 PM
From comet-ml post #18977:
I have to eat my words to friends about this comet. Looks just like Ikeya-Seki in 1965. A really beautiful Xmas present.
I got a series of images this morning but have no website, so one of the better ones appears in the nzastronomers site.
I estimated the visible tail length at 18 degrees, and the head was still out of sight below the local horizon here in New Plymouth, New Zealand.
Posted by: Mongo Dec 21 2011, 05:09 PM
From this Brazilian http://nevoeiro.org/blog/?p=740:
http://img.photobucket.com/albums/v455/mongo62aa/IMG_8597.jpg
Posted by: Mongo Dec 21 2011, 07:58 PM
From comet-ml post #18990 by Robert McNaught:
The tail was very obvious to the naked eye, rather brighter than the Milky Way in Circinus, Norma and Ara but not quite as bright as in Crux and Carina. The split between the dust and gas tails was clearly evident to the naked eye.
10x50 binoculars didn't show much more tail length, but structure was present, especially the "spine" along the southern edge of the dust tail, continuing past the bifurcation of the dust and gas tails. The end of the dust tail fades off very rapidly and naked eye, 10x50B and various photos have the tail reaching RA 15h54m Dec -40.0 (2000) The ephemeris position at that time was RA 17h02.3 Dec -34d56' (2000) giving a dust tail of 14.3 deg. The gas tail is perhaps 1 deg longer but fades away much more gradually and thus has a less well defined end point. The edges of the dust and gas tail are very sharply defined.
The tail brightness from the bifurcation towards the head was quite uniform, but as twilight progressed, the tail near the head became lost in the twilight and I didn't see the head visually or record it on photos. This is not a strong conclusion, as I had to move to a better location to find a lower horizon and the sky brightness probably beat me. I'd be reasonably confident that from tomorrow onwards I'll be able to make some meaningful statement about the visibility of the head.
To place this comet in the pantheon of modern comets (essentially subjective), I'd put it in the class of Hale-Bopp, Hyakutake and Bennett with this morning's view.
I'll try to get some photos up later today.
Cheers, Rob
Posted by: Mongo Dec 21 2011, 08:07 PM
Here is a photo from this morning by http://www.iceinspace.com.au/forum/showthread.php?p=800493#post800493 from Bendemeer, New South Wales, Australia:
http://img.photobucket.com/albums/v455/mongo62aa/W3221211453amCwyatt.jpg
Posted by: Mongo Dec 21 2011, 09:46 PM
Photo from http://users.tpg.com.au/vtabur/2011w3/2011w3.htm:
http://img.photobucket.com/albums/v455/mongo62aa/IMG_3175_a.jpg
Posted by: ugordan Dec 21 2011, 10:05 PM
Wow.
Posted by: scalbers Dec 21 2011, 11:06 PM
Very nice. Looks rather brighter than pieces of Milky Way in the image. With the help of Mongo's finder chart one can see Antares in the lower left corner, and Mu Scorpii to the upper right of the comet head.
On the spaceweather.com site there is a timelapse of the comet rising as seen from western Australia by Colin Legg. Worth looking at full screen:
http://vimeo.com/34007626
Posted by: Mongo Dec 22 2011, 12:07 AM
There are some incredible movies now available from the http://sungrazer.nrl.navy.mil/index.php?p=news/birthday_comet, which is linked to in the very first post in this thread.
First is http://sungrazer.nrl.navy.mil/images/lovejoy/lovejoy_20111215b_cor1.mov from STEREO/SECCHI COR-1B. Very spectacular -- you first see the comet approaching the sun from the lower right, then the headless tail receding to the upper left, then the tail-less comet nucleus moving away from the sun toward the lower right as it begins to generate a new tail.
Second is http://sungrazer.nrl.navy.mil/images/lovejoy/HI1A_Lovejoy_Dec16_20.wmv from STEREO/SECCHI HI-1A, also a very striking movie of the comet departing from the sun..
Posted by: Mongo Dec 22 2011, 03:11 PM
The latest image of Comet Lovejoy, by Colin Legg. The comet is starting to move into darker skies.
http://img.photobucket.com/albums/v455/mongo62aa/CometLovejoyReflections.jpg
Here is the latest report from Dave Herald from comet-ml post #19013:
Dave Herald
Murrumbateman, Australia
Posted by: Stu Dec 22 2011, 06:54 PM
Good grief... view from the ISS...
http://www.flickr.com/photos/nasa2explore/6555113049
Posted by: Tesheiner Dec 22 2011, 07:20 PM
Wow! 
Posted by: Stu Dec 22 2011, 08:44 PM
Lovejoy Rising...
|
Posted by: centsworth_II Dec 22 2011, 09:08 PM
This time lapse via a tip from http://twitter.com/#!/elakdawalla/status/149957523502415874
http://www.nasa.gov/multimedia/videogallery/index.html?media_id=125774121
Posted by: Stu Dec 22 2011, 09:12 PM
Just saw that, wish I'd noticed there were earlier images to begin the sequence sooner. Oh well...
Posted by: Mongo Dec 22 2011, 10:48 PM
From comet-ml post #19028 by Dave Herald:
The comet’s tail for the first 12+ degrees is definitely considerably brighter in surface brightness than the adjacent Milky Way band at similar altitudes. My comparison with the Magellanic clouds was of the tail at around 10 deg altitude, with the Magellanic clouds at 40 to 50 deg altitudes, with significant atmospheric absorption at low altitudes.
Re tail length. With the nucleus at 17h 00.6m –37d 10’ (but no condensation visible at that location), the dust tail extended to around 15h 44m, –43.0d, and the ion tail extended to about 15h 58m, –44.3d – giving tail lengths of around 16 deg.
Rob refers to P/ Halley 1986. IMHO, Lovejoy is MUCH more spectacular and visible than Halley was at its best. However it is considerably less spectacular than McNaught was at its best. Overall – it is in the category of ‘spectacular’ comets. Commiserations to those in the northern hemisphere, who won’t be able to see this marvellous Xmas comet.
Dave Herald
Murrumbateman, Australia
From: Robert McNaught
Sent: Friday, December 23, 2011 5:56 AM
To: Comets-ml
Subject: Re: [comets-ml] Comet Lovejoy Spotted From Space Station
Confirming Dave Herald's comment on the brightness of the tail, I made it brighter than the surface brightness of the Small Magellanic Cloud (SMC) on Dec 21.7 UT, but comparable to the LMC. A more subjective comparison (again) would make it much more impressive than P/Halley in 1986 which I saw pretty much every night for over a month after perihelion.
Cheers, Rob
Posted by: Mongo Dec 22 2011, 10:53 PM
Here is a cropped version of the full-resolution photo of the comet from the ISS:
http://img.photobucket.com/albums/v455/mongo62aa/iss030e014350.jpg
Posted by: Mongo Dec 22 2011, 10:58 PM
I like this shot, taken by Jim Gifford, it is very atmospheric:
http://img.photobucket.com/albums/v455/mongo62aa/1ACAE7FA231C40F8BE256BA89796C1FD.jpg
Posted by: Mongo Dec 23 2011, 12:35 AM
From comet-ml post #19031 by David Seargent:
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
Posted by: Mongo Dec 23 2011, 01:57 AM
A great photo by Lester Barnes of south Australia:
http://img.photobucket.com/albums/v455/mongo62aa/1d5bf314.jpg
Posted by: Mongo Dec 23 2011, 01:29 PM
Commentary by John Bortle (comet-ml post #19037) on the photo just above this post, by Lester Barnes:
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
Posted by: Mongo Dec 23 2011, 01:34 PM
From comet-ml post #19038, replying to David Seargent's post:
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.
Posted by: Mongo Dec 23 2011, 01:42 PM
Another report on the comet by Geoff Dudley (comet-ml post #19039):
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:
http://img.photobucket.com/albums/v455/mongo62aa/IMGP1929.jpg
Posted by: Mongo Dec 23 2011, 02:00 PM
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:
No points in this category.
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.
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
Posted by: Mongo Dec 23 2011, 07:04 PM
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:
Got a few nice snaps too but I've only had time to put up this one:
http://img.photobucket.com/albums/v455/mongo62aa/IMG_3221_a.jpg
Posted by: Mongo Dec 23 2011, 07:15 PM
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.
http://img.photobucket.com/albums/v455/mongo62aa/comparison-1.jpg
Posted by: Mongo Dec 23 2011, 07:21 PM
The tail is getting bigger! From Rob Kaufman in comet-ml post #19045:
http://img.photobucket.com/albums/v455/mongo62aa/C2011W323Dec201155mmtextsm.jpg
Posted by: Mongo Dec 23 2011, 10:42 PM
From Robert McNaught, comet-ml post #19047:
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.
Until tomorrow night.
Cheers, Rob
He also linked to several outstanding photos that he had taken:
http://img.photobucket.com/albums/v455/mongo62aa/Lovejoy11Dec21_closeup.jpg
http://img.photobucket.com/albums/v455/mongo62aa/IMG_4253.jpg
Posted by: Mongo Dec 23 2011, 11:08 PM
More confirmation of today's observations, by Chris W in comet-ml post #19050:
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.
Posted by: Mongo Dec 24 2011, 03:53 AM
A response by Vello Tabur in comet-ml post #19055 to Rob McNaught's post #19047, two posts above this one:
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
Posted by: elakdawalla Dec 24 2011, 04:03 PM
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.
Posted by: ElkGroveDan Dec 24 2011, 04:13 PM
Ditto. I've been thinking about driving to Argentina. http://www.mapcrow.info/cgi-bin/cities_distance_airpt2.cgi?city3=1591%2CS&city4=-1456711%2CB
Posted by: Explorer1 Dec 24 2011, 06:46 PM
That would be rather tricky, considering the http://en.wikipedia.org/wiki/Dari%C3%A9n_Gap...
Posted by: Mongo Dec 24 2011, 07:42 PM
Christmas Eve image of comet Lovejoy by Scott Alder:
http://img.photobucket.com/albums/v455/mongo62aa/Scott-Alder-lovejoycomet_1324729062.jpg
Posted by: nprev Dec 25 2011, 01:36 AM
W O W ! ! !
Posted by: Mongo Dec 25 2011, 02:08 AM
Yes, I think that Lovejoy has done quite well for a comet that was not supposed to survive perihelion.
Posted by: Mongo Dec 25 2011, 02:55 PM
From comet-ml post #19078 by David Seargent:
Posted by: Mongo Dec 25 2011, 07:41 PM
From comet-ml post #19088 by Robert McNaught:
> Actually I do not think that nucleus has dissipated. Activity just fade
> quickly, but apparently there is still something huge producing much more
> material into tail and coma, unlikely swarm of debries.
Thanks Jakub,
I tend to agree that there is an "invisible" mass responsible for the hood and spine. The tail is showing no signs of becoming a ghost. I've put up a processed Uppsala image from last night (Dec 24.7UT).
http://msowww.anu.edu.au/~rmn/C2011W3.htm
It continues to show a well defined parabolic hood and the spine narrowing basically to an "empty" point pretty much on the edge of the parabola. Trying to image it now, but there is cloud and I can't get a focus sequence.
My astrometry of the tip-of-the-spine will perhaps tell one way or another whether this is a substantial mass or displaying significant short-term non-gravitional effects. Give it a week and we should a good handle on the dynamics.
The tail continues to fade (Dec 25.7UT) and is very significantly less bright than on Dec 21. There was quite a similarity to Hyakutake tonight, partly due to the tail being so long, narrow and "ghostly". There is no real comparison though, as there is no coma and condensation, which were both prominent in Hyakutake. On Dec 21 though, the tail surface brightness was sufficient to put it in the "awesome" category for me. Very much on par with Hyakutake, Hale-Bopp and Bennett. Tonight it was much more Halleyesque. I'll reply to the great comet listing thread in a day or so as I've been keeping such a list (and noting other folks lists) for a couple of decades.
Posted by: Mongo Dec 26 2011, 02:30 PM
Comet-ml post #19096 by Rob Kaufman:
http://img.photobucket.com/albums/v455/mongo62aa/W321-25Dec2011ver2.jpg
Anyway, the massive expansion is pretty clear. Hoping to get another great view of this 'megacomet' in the morning.
Cheers -
Rob Kaufman
Bright, Vic, Australia
Posted by: Mongo Dec 26 2011, 02:35 PM
Comet-ml post #19100 bt Dave Herald, regarding the visual brightness of comet Lovejoy:
The main issue is how you might represent the brightness of the comet's tail. I think the best way to describe this is that the comet is currently close to one of the brighter parts of the Milky Way, and compared to the milky way at the same altitude, the surface brightness of the majority of the tail is somewhat brighter than the brighter parts of the Milky Way.
Dave Herald
Murrumbateman, Australia
Posted by: Mongo Dec 26 2011, 02:37 PM
Comet-ml post #19101 by Rob Kaufman:
Cheers -
Rob
Posted by: Mongo Dec 26 2011, 08:37 PM
From comet-ml post #19115 by Jim Gifford:
Posted by: Stu Dec 26 2011, 09:07 PM
Latest ISS shots put together...
|
Posted by: Mongo Dec 26 2011, 09:28 PM
From comet-ml post #19117 by Rob Kaufman:
As the tail fanned out the surface brightness diminished although it was quite clear as far as the top Pointer, a distance of 28-deg. Naked-eye I could make it out faintly to halfway between the top Pointer & the Southern Cross, about 33-deg. Nothing could be seen there with binoculars - in fact even the section adjacent to the Pointers was difficult to make out with binoculars. Photography seems to show some faint hints of dust extending to adjacent to the Cross (perhaps 38-deg) but I need to check some reference images to see if it's just fortuitously aligned bright patches.
Was it John Bortle who predicted the comet would expand & dim to became a huge 'ghost'? Because that's the impression I got. The comet would still be a striking sight away from the Milky Way, but even in amongst it I found the sight of this great ghost transfixing, a true wonder!
He also posted this image:
http://img.photobucket.com/albums/v455/mongo62aa/C2011W326Dec201117-00UT18mmfullredsm.jpg
Posted by: Mongo Dec 26 2011, 10:57 PM
Comet-ml post #19119 by John Bortle:
>
> Was it John Bortle who predicted the comet would expand & dim to became a huge 'ghost'? Because that's the impression I got. The comet would still be a striking sight away from the Milky Way, but even in amongst it I found the sight of this great ghost transfixing, a true wonder!
>
> Rob Kaufman
> Bright, Vic, Australia
>
At this time I would hasten to point out that based on descriptions of the Post-T evolution so far, 2011 W3 is almost precisely mimicing the physical appearance of the Great Southern Comet of 1880 during it apparition.
If this continues I would predict that by about next weekend 2011 W3's tail will have assumed essentially the same low level of brightness over virtually its entire length. As it fades toward obscurity, it will attain a maximum length between 50 and 60 degrees as seen from the darkest observing sites, but be exceedingly faint and ghostly in its appearance. At the same time the head will fade way completely, the sunward end of the tail simply fading to nothingness against the sky.
Incidentally, my main computer is down and I'm working from a tiny and frustrating laptop, so please forgive typing errors. I'm also unsure just how much I will be able to participate on the forum this week until my big machine returns.
J.Bortle
Posted by: Mongo Dec 27 2011, 02:47 AM
Comet-ml post #19122 by David Seargent
This morning (Dec. 26, 1600-1650 UT) about 37 degrees of tail could be seen from Cowra, reaching up to the outer edges of the Southern Cross. Interestingly, this was the first time that something that could be called a "head" was discernible in the 25x100 BT. At the end of the tail, there was a small (approx 4 arcmin) very diffuse, transparent nebulous blob slightly brighter than the adjoining tail (m = 5.3). The distinction between "head' and "tail end" was more apparent using averted vision, but it was truly there! The two earlier sungrazers that I saw developed in a similar way, albeit much later after perihelion. Ikeya-Seki about 7 weeks after perihelion and White-Ortiz-Bolelli about 3. I would guess that the early diffusing of 2011 W3 probably signifies a small comet shutting down whilst still closer to the Sun rather than one that is disintegrating. On the other hand, the tail (although much fainter) is still very distinct and remains impressive in a dark sky. The length is truly amazing ... lengthening even while it fades!
Cheers,
David
Posted by: Mongo Dec 27 2011, 02:54 AM
Comet-ml post #19122 by Vello Tabur
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.
http://img.photobucket.com/albums/v455/mongo62aa/IMG_3273_a_25.jpg
Vello
Posted by: Mongo Dec 27 2011, 05:49 PM
From comet-ml post #19128 by Michael Mattiazzo:
http://img.photobucket.com/albums/v455/mongo62aa/2011w3_20111226_mm6b.jpg
Posted by: Mongo Dec 27 2011, 08:02 PM
A spectacular image hosted on Gary Kronk's http://cometography.com/ website. Photo taken by Gordon Garradd on December 22:
http://img.photobucket.com/albums/v455/mongo62aa/2011W3_20111223_GG.jpg
Posted by: Mongo Dec 29 2011, 02:00 AM
Comet-ml post #19131 by Andrew Pearce:
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
Posted by: Mongo Dec 29 2011, 11:02 PM
Comet-ml post #19142 by Andrew Pearce
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
Posted by: Mongo Dec 31 2011, 01:13 AM
Comet-ml post #19150 by Chris:
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
Posted by: Mongo Dec 31 2011, 02:15 PM
From comet-ml post #19154 by Michael Mattiazzo
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.
Posted by: Mongo Jan 1 2012, 06:39 PM
Comet-ml post #19169 and #19174 by David Seargent
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
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
Posted by: Mongo Jan 1 2012, 06:43 PM
Comet-ml post #19176 by John Bortle:
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
Posted by: nprev Jan 2 2012, 03:28 AM
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.
Posted by: Mr Valiant Jan 2 2012, 03:10 PM
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 
Many thanks to UMSF for this absorbing thread.
Posted by: Juramike Jan 3 2012, 02:11 AM
Some nice images of Comet Lovejoy on Guillermo Abramson's flickr site:
http://www.flickr.com/photos/12759894@N06/6623516639
Posted by: Mongo Jan 3 2012, 01:48 PM
Comet-ml post #19187 by David Seargent
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
Posted by: Mongo Jan 3 2012, 01:50 PM
Comet-ml post #19188 by David Seargent
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
Posted by: Mongo Jan 3 2012, 11:13 PM
Comet-ml post #19197 by John Bortle:
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
Posted by: Mongo Jan 3 2012, 11:19 PM
Comet-ml post #19201 by Richard Miles:
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.
I agree that a temporary surface crust of material can form, but not as you have envisaged here.
One key factor here is that time near closest approach is relatively short - i.e. the nucleus remained within 5 solar radii of the barycenter for about 6 h, and 2 solar radii for just 1.5 h. You have to consider both the solar electromagnetic radiation flux and also the flux of high energy baryons / charged particles, typically protons travelling at speeds of ~500 km/s. The initial effect of these is to strip away any "umbrella of dust particles" leaving the bare nucleus exposed to the 'onslaught' from the Sun.
A more likely scenario may involve a Leidenfrost-type phenomenon. Here's how I see it:
A large fraction of the near-surface material within the nucleus is likely to melt. The surface tension between the melt and any residual solids provides significant mechanical strength, more especially if most of the refractory solids are in the 1-1000 micron size range. This process temporarily inhibits physical break-up. Now if you assume a large fraction of the incident energy (electromagnetic radiation and particle kinetic energy) is absorbed by the surface, this will cause a proportion of the molten material to vaporize - but how much depends on the latent heat of vaporization of the material and the time-scale involved. The vapour boiled off from the melt is in effect a thin gaseous atmosphere, which will increase in pressure until a temporary bow-shock front develops. It is this bow-shock effect which may act as the "umbrella" - a "parapluie" could be more descriptive a word for this. If the gas pressure behind the bow-shock reaches a sufficient magnitude (Poiseuille conditions of P and T arise), particulates will also be entrained in the gas flow. Given this scenario, the surface of the nucleus can be shielded to a degree by two processes; (a) partial deflection of the intense oncoming solar wind by the bow-shock, and ( b ) particulates suspended in the temporary gas layer absorb some of the e-m radiation and re-radiate it back into space. Overall this creates a type of Leidenfrost effect and a temporary pseudo-steady state enabling the nucleus to survive perihelion passage.
Remember, although H2O ice is an important constituent, as the thermal regime evolves to higher and higher temperatures, different materials which are normally solid will each begin to melt and play a significant role.
What will be important now is to characterise the nature of any remaining particulates close to the centre of any debris field using large ground-based telescopes or the HST. Let's hope such observations are successful.
The fate of the nucleus depends on what happened post-perihelion. Sufficient time has passed such that, given the very large thermal gradients, significant heat conduction to the central region of the nucleus would have occurred. You then have a complex situation in which solids melt, liquids vaporize and internal gas pressures develop leading to gradual disintegration of the nucleus. What debris remains will be to an extent an assay of the more refractory material from deep within the original nucleus.
Richard Miles
BAA
Posted by: Mongo Jan 3 2012, 11:23 PM
Comet-ml post #19202 by Robert McNaught:
Cheers, Rob
Posted by: Mongo Jan 3 2012, 11:27 PM
Comet-ml post #19203 by Richard Miles:
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!
John - Allow me to follow through one possible interpretation based on my earlier description of the near-perihelion scenario:
We talk about dust (i.e. refractory particles ejected from the nucleus) and gas (low-boiling point volatiles) but there has to be a third type of particle created in the case of a sungrazer nucleus. This material is in effect the "smoke' which is created when otherwise fairly refractory material is vaporized and is able to recondense to an extent.
Two mechanisms generate this "smoke". One is created in the scenario I have already described. The temporary gas shell / bow shock feeds molecules of vaporised refractories into the comet's tail. As the gas pressure and temperature within the tail declines from Poiseuille conditions towards Knudsen conditions, a dynamic situation unfolds whereby many of these molecules collide and stick together building up extremely fine, sub-micron size refractory condensates - in essence a newly-created dust or "smoke" forms.
A second mechanism can also contribute, i.e. sputtering of the surface of the nucleus by fast, highly energetic particles in the solar wind. Calculations would need to be done to see whether enough "smoke" could be created via sputtering of the surface in the time available - I somehow doubt that this can be the entire explanation.
So taking these hypotheses into account, how can we explain the absence of the "sheath" in other very small "q" non-Kreutz comets. My interpretation here is that if the nucleus is too small it cannot build up a stable melt zone within the near-surface, so no temporary envelope of volatilized refractories and no bow-shock can form. Under such conditions, refractory materials will still volatilze but will not experience the conditions required for particles to seed and grow by molecular collision. Such refractory molecules fail to condense along with others, hence no "smoke" can form. This may explain the absence of the "sheath" seen in larger Kreutz sungrazing comets.
Richard Miles
BAA
Posted by: Mongo Jan 5 2012, 03:42 PM
Comet-ml post #19210 by David Seargent
John - I agree that the comet most probably has made a previous perihelion passage as an independent body, but it may not necessarily have been an independent COMET. Although unlikely, it is possible that it may have broken away as a secondary nucleus while the parent was still moving toward its previous perihelion. The situation would then be a little like the Marsden sunskirters C/2004 V9 and V10. Sekanina has shown that V10 broke away from V9 about 3 months prior to its previous perihelion passage, at which the split comet was observed as C/1999 J1 (albeit not resolved into two nuclei in the SOHO images). Interestingly, the circumstances of this disruption meant that the smaller V10 (although discovered after V9) reached perihelion before V9; the opposite of what happens when comets split at or shortly after their previous perihelion passage. IF something similar has happened with W3, it is likely that the primary nucleus is still on its way and probably not very far away!
Please, nobody read this as a prediction of another bright sungrazer in the near future. There is no real reason to think that W3 did break away from a larger object just prior to its previous perihelion, only that this remains one possibility. But it might be wise to monitor the inward path of the Kreutz group just in case...!
Cheers,
david
Posted by: Mongo Jan 5 2012, 03:45 PM
From comet-ml post #19209 by Ian Cooper
I found it relatively easy to see. The brightest section was where it passed through the brighter stars of Apus and Chamaeleon. I was even sure that I could see that part before the moon set.The darklanes in that region were easy to detect with the naked-eye, usually a good sign of transparency.
Posted by: Mongo Jan 5 2012, 03:51 PM
Comets-ml post #19210 by Michael Mattiazzo
I observed comet C/2011 W3 Lovejoy this morning near the vicinity of Castlemaine, Victoria.
I have uploaded a photo taken 2012 Jan 4.69UT to my website:
http://members.westnet.com.au/mmatti/sc.htm
Approximately 10 degrees of tail was observed with the unaided eye using averted vision, extending just beyond Alpha Apus.
The intensity has dropped off substantially since my last observation on Dec 30.71, and is now a very difficult naked eye target.
Through 8x40mm Binoculars, the tail extends through to Beta Chameleonis for a total of 20 degrees.
Photographically the tail length is about 30 degrees, passing near Beta Carinae.
Interestingly the brightest section of tail now appears to be at the head of the comet, wheras previously it was some distance along the tail.
I estimated the head section to be about magnitude 6.5
I could offer an explanation - the the head section is now closest to Earth, in a few days time.
Comments are welcome.
cheers,
Michael Mattiazzo
Castlemaine Vic.
This report is quite different from the report by Ian Cooper just before it. I attribute the difference to the (presumably) much better sky conditions that Ian Cooper was under when he observed the comet.
Posted by: Pertinax Jan 5 2012, 06:04 PM
Hey Mongo,
Thank you for your posts of interesting obs and tidbits from Comets-ml. I for one very much appreciate it! 
-- Pertinax
Posted by: Mongo Jan 5 2012, 07:10 PM
Thank you for your kind words, Pertinax. They do serve to motivate me to continue updating this thread.
Comets-ml post #19215 by John Bortle, in reply to post #19210 by David Seargent (#109 on this thread)
In my mind this possibility also arises concerning the 'apparent' spate of sungrazers in the late 18th century. How many additional such objects might have appeared then during the annual intervals when Kreutz sungrazers might only have been seen from the Southern Hemisphere and went totally unreported? Lots of interesting conjecture is possible in this area with our knowledge of the sungrazer family so incomplete!
J.Bortle
Posted by: Mongo Jan 7 2012, 03:15 PM
Comets-ml post #19225 by Rob Kaufman
http://img.photobucket.com/albums/v455/mongo62aa/gifanimW304-05Jan2012UTJTilbrook.gif
Cloudy/hazy last two nights here so I will now have to wait till late this coming week.
Cheers -
Rob Kaufman
Bright, Victoria, Australia
Posted by: Mongo Jan 12 2012, 01:58 PM
From Comets-ml post #19236 by Ian Cooper:
I could detect it as a persistent, elongated haze seemingly attached to the Bar of the LMC at the Tarantula nebula end. I could just see it with direct vision a few times. The cleanest view I had was at 9.36 U.T. by which time I was reasonably dark adapted and the comet's part of the sky was still relatively black. I traced the tail to 8 degrees before it merged with the LMC. Binoculars did not improve the view. Transparency was not great for most of the time with clouds trying to form in that area, but they moved on and leaving the constant glow behind. It reminded me of some very faint spindle galaxies that I have observed over the years.
Posted by: galileo Jan 13 2012, 04:44 PM
Mongo thanks for the great updates. I'm from the states and currently have a friend in Sydney, is it possible for him to see this comet from his location and if so what az and el would I tell him to look in order to see it. Thanks again for the great updates it has been interesting to follow.
Posted by: Sunspot Jan 13 2012, 06:03 PM
I think it's more a photographic target now.
Posted by: Mongo Jan 18 2012, 04:38 PM
A compilation of recent posts about 2011 W3 Lovejoy:
From comets-ml post #19273 by Con Stoitsis:
At it's peak around Christmas time, the comet sported a tail over 30 degrees in length, and was easierly visibly in the morning sky
I will never forget how it looked over the SE horizon.
As mentioned, the comet has now faded greatly, and is well below naked eye visibility.
I could not detect it in my 70mm binoculars from an relatively dark sky a couple of days ago, but I did read a report yesterday, where it was detected in small binoculars from a loction with an exceptionally dark sky.
From comets-ml post #19275 by Paul Floyd:
From comets-ml post #19276 by David Nicholls:
It's very annoying when you know there's a bright comet in the wrong hemisphere :-(
From comets-ml post #19277 by Rob Kaufman:
From comets-ml post #19278 by Chris W.:
The most exciting part of W3 Lovejoy for me was the first time i saw it, like a headlight beam over the horizon, Michael Mattiazzo was on the receiving end of a very excited phone call from me that morning!
After flicking through David Seargents book "The Greatest Comets In History" there was a drawing or painting or something of the Great Comet of 1880, which reminded me of this comet, the way it's angled and the "beam" look it had about it, it's like you're taking a trip back in time, incredible!
I eagerly await further findings from W3 in future, it was a lesson learned!
Posted by: Mongo Jan 19 2012, 03:09 PM
Comets-ml post #19281 by John Bortle:
Although most often used to designate some truly extraordinary, brilliant, long-tailed comet, prior to about 1850 the name was occasionally applied simply to some moderately bright comet that happened to appear in a given year. In other instances some truly outstanding objects were initially widely known by the name of their discoverer, only gaining the prefix 'Great Comet' after their apparition ended. The name has also often been affixed to bright comets that have appeared suddenly out of the twilight and were spotted by so many that no specific first discoverer(s) could be determined and it was easier to do so.
However, the more accepted modern interpretation seems mainly to center around comets of extreme brilliance and possessing long bright tails. Even so, any critical determination is still dubious enough that various authors can differ in their lists of 20th/21st century examples and particularly in their pecking order.
From my own viewpoint I regard Comet Lovejoy as probably making the 'Great Comet' cut, but only just barely. I would tend to group it along with the Great Southern Comets of 1880 and 1887 as a marginal member of the clan. The two earlier comets gained the title mostly by virtue of their impressive tails and sudden appearance, as their heads were never seen as very bright in a reasonably dark sky (the 1887 object even lacked any head!). In fact, these three objects are likely the 'faintest' in terms of coma brightness among all of the Great Comets in history.
J.Bortle
Posted by: Mongo Jan 19 2012, 03:11 PM
Comets-ml post #19285 by David Seargent:
Regards,
David
Posted by: Paolo Jan 19 2012, 07:35 PM
speaking of sungrazer comets, tomorrow's "Science" has a paper on one of them:
http://www.sciencemag.org/content/335/6066/324.abstract
see also http://www.sciencemag.org/content/335/6066/296.summary
of course, both require a subscription
edit: even if you don't have a subscription, be sure to check the supplementary material for the paper and download the two awesome videos!
Posted by: Mongo Jan 19 2012, 09:30 PM
Hello all,
On http://www.unmannedspaceflight.com/index.php?s=&showtopic=7145&view=findpost&p=181726 of this thread I referenced a "Great Comet rating system" that I had first used here at the time of 2007 McNaught. While better than nothing, that system was far from perfect, full of arbitrary cutoffs and (probably) incorrect weightings for various comet attributes, as well as some more serious issues.
Is there interest here in putting together a more logical rating system for comets visible by naked eye from Earth, starting with the basic "ground rules" to be followed in setting up the system, followed by determining what comet attributes will be considered and what points will be awarded for a given magnitude of that attribute?
There are surely interested people here who could contribute to such an effort, if I do get a positive response. If we do decide to go ahead, I will probably start a new thread for the effort.
Posted by: ngunn Jan 19 2012, 11:01 PM
I would suggest two ratings: the time integral of the of the apparent magnitude of the comet and the time integral of its absolute magnitude. That would be enough, I think, if those quantities could be determined from the observations. I'm sure we could do that now but maybe the historical data are insufficient.
Posted by: Mongo Jan 19 2012, 11:47 PM
I had been thinking along similar lines, although I had also been thinking about separating each comet's rating into a "peak" rating (the rating for the brightness + tail length + possibly other attributes (visible all night, multiple tails, etc.) on the particular day that the computed daily rating is at its greatest) and a "career" rating, summing the individual daily ratings into one rating, which would result in higher numbers for a longer term of naked-eye visibility.
The problems for this approach would be: one, this would involve a lot of work finding the daily measurements and entering them into a spreadsheet (one row for each day of visibility), and two, the information would simply not be available for earlier Great Comets. It should still be possible for the more recent comets, which presumably are the ones of most interest.
This is definitely one area that needs to be improved; the current system combines the tail brightness from the day that the brightness is at its maximum, with the tail length from the day when the visible tail length is at its maximum, as if they were on the same day, which is clearly incorrect (plus adding points for a daylight comet, which would be from yet a third day). I think that computing a rating for each day is the way to go, if the data is known.
I do think that ideally, we should use more than just the apparent and absolute magnitudes of the comet, since the impressiveness of the tail as seen from a dark-sky site does matter.
Posted by: nprev Jan 21 2012, 07:03 AM
All good things must come to an end, and that aphorism is most apropos for Sun-grazing comets.
As a coda for this thread, here's a shot taken by one of my stepdaughter's fellow travelers in Chile at the end of December.
Farewell, Lovejoy, and thanks.
|
Posted by: Mongo Mar 9 2012, 03:04 AM
Science papers about Lovejoy are starting to appear:
http://xxx.lanl.gov/abs/1203.1808
Two very big Kreutz group comets, 1882 II and 1963 V were observed within the Roche limit of the Sun (R1882II = 30.7 km and R1963V = 13.7 km; Knight et al., 2010). The perihelion distances were rp;1882II = 1:67 Rsun and rp;1963V = 1:09 Rsun, respectively. Comet 1882 II had broken into at least five fragments (Gill, 1883). This obersvation is in agreement with our model, because the estimated radius of comet 1882 II was bigger than the derived maximum radius for the survival of sungrazing comets within the Roche limit. The survival of comet 1963 V can be explained with our model within the error of our model and the error of the size estimation.
Posted by: Sunspot Mar 10 2012, 01:45 AM
Looks like we may have another bright sungrazer on March the 16th
Posted by: Mongo May 29 2012, 02:07 AM
http://xxx.lanl.gov/abs/1205.5839
We describe the physical and orbital properties of C/2011 W3. After surviving perihelion, the comet underwent major changes (permanent loss of nuclear condensation, formation of spine tail). The process of disintegration culminated with an outburst on December 17.6 (T+1.6 d) and this delayed response is inconsistent with the rubble pile model. Probable cause was thermal stress from the heat pulse into the nucleus after perihelion, which could also produce fragmentation of sungrazers far from the Sun. The spine tail was a synchronic feature, made up of dust released at <30 m/s. Since the nucleus would have been located on the synchrone, we computed the astrometric positions of the missing nucleus as the coordinates of the points of intersection of the spine tail's axis with lines of forced orbital-period variation, derived from orbital solutions based on preperihelion astrometry from the ground. The resulting osculating orbital period was 698+/-2 years, which proves that C/2011 W3 is the first major member of the predicted new, 21st-century cluster of bright Kreutz-system sungrazers. The spine tail's tip contained dust 1-2 mm in diameter. The bizarre appearance of the dust tail in images taken hours after perihelion with coronagraphs on SOHO and STEREO is readily understood. The disconnection of the comet's head from the preperihelion tail and the apparent activity attenuation near perihelion are both caused by sublimation of all dust at heliocentric distances smaller than ~1.8 solar radii. The tail's brightness is strongly affected by forward scattering of sunlight by dust. The longest-imaged grains had a radiation-pressure parameter beta ~ 0.6, probably submicron-sized silicate grains. The place of C/2011 W3 within the hierarchy of the Kreutz system and its genealogy via a 14th century parent suggest that it is indirectly related to the celebrated sungrazer X/1106 C1
Posted by: Paolo Jun 6 2013, 07:13 PM
comet Lovejoy in tomorrow's Science:
http://www.sciencemag.org/content/340/6137/1196
while the paper is behind the paywall, you can see http://video.sciencemag.org/VideoLab/sungraze/
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