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The Great "Birthday Comet" of 2011, Chapter 1: Inbound.

This page was created on December 2nd, 2011, the 16th "birthday" of the SOHO satellite, and the day of the announcement of the discovery of a potentially very bright Kreutz-group comet, C/2011 W3 (Lovejoy). This page chronicled the latest news relating to this discovery of, build-up to, and appearance of this object in the SOHO and STEREO fields of view. We did not anticipate just how spectacular this event would become as the comet reached, and survived, perihelion. Therefore this chronology has been broken into two parts: "Inbound", and "Survival".




Dec 2nd, 2011

1300UT: I arrive to work to find my inbox full of messages about the posting of object TLc001 to the NEO Confirmations web page hosted by the Minor Planet Center (MPC). The object is simply stated as:
Object   H     G    Epoch    M    Peri.      Node       Incl.        e      n   a          NObs NOpp   Arc    r.m.s.    Orbit ID
TLc001  14.4  0.15  K11BF        59.80082  335.88141  136.91924  1.0000000     0.0000000     14   1    1 days 0.47      NEOCPNomin
This equates to the orbit of a Kreutz-group comet, albeit rather fuzzy at this moment. It will take a couple of night of observations before the MPC can put out a confident orbit and officially declare this object as real.

1600UT: It has come to my attention that this object was first reported by Australian astronomer Terry Lovejoy. This discovery details are still unclear to me but even if the comet does not bear his name (i.e. it gets named after some sky survey), he will still be the first person to discover a Kreutz-group comet in both space and ground-based telescopes! Terry was one of the pioneers in SOHO comet hunting, and I think SOHO-74, aka C/1999 O1 (SOHO), was his first discovery. So many congratulations to him!

1540UT: This is a good time to add in notes of caution about this object as I don't want this to turn into some "Elenin-like" event whereby folks get whipped up into a frenzy about an object that ultimately does not perform. So here it is: we only have a few rather mediocre observations of this comet, it is still very faint (mag 15), and is already a difficult object to observe due to its location in space. Several possibilities exist now:
1. It could be a huge bright Kreutz, like the "great" comets of the 1880's, or Ikeya-Seki in 1965
2. It could just be a nice bright Kreutz like some of the ones we've seen over the past couple of years in SOHO and STEREO
3. It could be a somewhat large but not altogether enormously bright Kreutz like Comet White in 1945
4. It could be too fragile and disintegrate before it reaches out cameras
If I had to guess, I'd say somewhere between #1 and #2 is what we'll get -- a pretty big, bright Kreutz with a nice bright tail. I base this prediction entirely on speculation and hope.

1904UT: And it's official! Comet C/2011 W3 (Lovejoy) has been announced on MPEC 2011-X16. Many congratulations to Terry!

2000UT: A little more about the orbit of this comet and then I'm done for today. The preliminary orbit states perihelion (closest approach to the Sun) as occurring on Dec 15.99997 (let's round up a tad and say "midnight") at 0.0058936AU, which is a little over 1.2 solar radii. So this comet is a true "Sungrazer", and will skim approximately 140,000km above the solar surface. That's really close, so unless this was a very large comet -- which it won't be -- then I can not imagine it surviving this encounter.

As for brightness, the MPEC lists peak m1 as being around mag 4. I'm going to stick my neck out and say that this is very conservative. If the comet survives to near perihelion, I would not be surprised to see something more like mag -2 or -4. And if this turns out to be more like Ikeya-Seki (highly unlikely), it could be closer to mag -10 and visible in broad daylight! However, I do NOT think the latter scenario is likely at all.

One final closing remark for today, just to head off inevitable questions: No, this comet will not pass near Earth or any other planet; No, this comet will not affect or interact with Earth or any other planet in any other way; No, this is not a giant comet, a "second Sun", or any other kind of harbinger of doom; No, this comet will not affect the Sun in any appreciable way. (Had to get that out there early...)

Dec 3rd, 2011

1300UT: Terry Lovejoy has posted an account of his discovery to the excellent comets-ml mailing list.

Also the guys at GSFC have a story up about this object on the main SOHO web page. We will work closely together to keep both of the sites up-to-date with the latest information and developments with this object. Over the coming days we should get more ground-based images of the comet and, hopefully, a clearer picture of how bright it is now and some better estimates of how bright it will get in the SOHO and STEREO images. (I have correspondence from a highly-reliable coleague who I won't name here; he thinks we could have a "worst case" of mag 2 brightness. He seems disappointed at that. I'm not! But he does then go on to less cautiously state that he thinks mag -2 is actually quite plausible for a peak brightness. I like that answer even better!)

Dec 5th, 2011

Several images of C/2011 W3 (Lovejoy) have been obtained from the ground now including by Terry Lovejoy himself, who reports visual observations of his comet on December 3rd, stating a visual magnitude of m11.6. So the comet is clearly brightening up, which is great news. From my own observations of Kreutz-group comets, having personally viewed approximately 1,600 sungrazing comets, I can say with confidence that they all brighten at least three or four orders of magnitude during their final day, and I have seen them increase as much as 12 orders of magnitude when moving between the SECCHI HI-1 and the LASCO C2 imagers. They seems to be a very unpredictable thing, though, and they exhibit a broad range of brightness behavior and morpholgy (shape/size, etc). This one is a very unknown quantity given that it's the first ground-discovered Kreutz since 1970, so it is just impossible to know for sure what it will behave like, and I would not trust anyone that claims they know exactly what this comet will do. That said...

I'm going to stick my neck out and say that m1=2 is a conservative estimate and I predict we'll see something closer to m1=-3. There has also been some discussion of whether this comet will survive its passage past the Sun. Again I wil stick my neck out and say that I do NOT believe that this comet will survive perihelion in any appreciable form. If the viewing geometry is right, I think we'll see some of the dusty tail sweep out beyond the Sun but I really don't think there will be any nucleus left; the comet just isn't bright enough already.

So now we've had time to play with the comet ephemeris (actually Dr. Bill Thompson at NASA GSFC has done this... he's amazing at this kind of thing), we can say with much more confidence when the comet will enter our imagers. This information basically rephrasing information I obtained from Dr. Thompson.
1. The comet should enter the STEREO/SECCHI HI-1B images on Dec 11, and HI-1A on Dec 12, midway along the bottom edge of both cameras.
2. The comet will enter the SOHO/LASCO C3 field of view early on Dec 14
3. The comet will enter the STEREO/SECCHI COR-2 A & B fields of view early on Dec 15 (UT time), and the COR-1 fields later that day.

We do now know that comets can be seen in extreme ultraviolet (EUV) images, so we are particularly interested in what the SDO and STEREO/SECCHI EUVI cameras can obtain. For SDO, the comet will be behind the Sun for perihelion, which is unfortunate. For EUVI on STEREO-A, the comet will remain above the solar limb throughout its passage, and will transit the solar disk for STEREO-B. I am trying to twist some arms to get lots of high-cadence images for EUVI for the relatively brief period during which the comet will be in the field of view.

Dec 8th, 2011

Things are looking good for C/2011 W3 (Lovejoy)... aside from that whole imminent destruction thing, of course! Ground observations are becoming trickier as it gets closer to the Sun, particularly for those in the Northern Hemisphere. However, reports are still coming in and the consensus seems to be that the comet is brightening! Of course this is what we expected, but it's reassuring nonetheless. There are some very nice images going online too, showing an increasingly condensed nucleus and nice diffuse tail on the comet. I still do not believe that this object will survive perihelion, but I do think that it will put on a spectacular show for us and will be the brightest Kreutz-group comet that SOHO has ever observed. I stand by my mag -3 prediction.

So as I mentioned, this comet is becoming increasingly tricky to observe from Earth and I think that in a few days time it will be essentially impossible to see any longer from the ground. But fear not! We have a fleet of sun-watching spacecraft that plan on turning their eyes towards Comet Lovejoy! I have been in contact with several operations teams for solar spacecraft (and indeed share a building with some of them), and so far we have the following plans:
1. STEREO/SECCHI: This will be the first spacecraft to get a clear view of the comet, and in fact it has been visible in our HI-2A imager for the past few days now, albeit faintly. As the comet approaches perihelion, we will perform our routine COR-2 observations until it reaches the COR-1 (inner coronagraph) camera late on the 15th. We will then focus our attention on that and the extreme ultraviolet (EUVI) instruments. The STEREO spacecraft are very far from Earth and so this only gives us a pretty small amount of data to send back. So we're going to have to go careful with what we do, and be clever about it. We are considering taking "subfield" images -- that is, only return, say, the top half of the image. We also have some on-board storage space that we can use but it still takes a long time to dump that data, and we're supposed to use that storage space to capture CME events. But I can make the case for an exception here.
2. SOHO/LASCO: The comet will enter LASCO C3 on the 14th at the very lower-left edge of the field of view. I predict it will be around mag 5 or 6 at this time. We are unable to squeeze any more images out of LASCO than we already do, simply because it uses early 1980's computer technology and just can't do things all that fast. So this means the standard 5 images per hour. What we can and will do, however, is use different exposure times and filters to capture as much science as we possibly can. Finally, the rarely-mentioned UVCS instrument on SOHO has the ability to point itself at a the track of the comet and get some observations. This has happened before with great success and so that's what we're shooting for again.
3. SDO: In July of this year, the NASA SDO spacecraft observed a comet evaporating in the solar corona: the first ever observations of its kind. I'm involved with a group of scientists that are still analyzing that event (exciting publication pending!), and we're naturally very excited about this opportunity. Unfortunately, it's now 6-months later which means that the comet will reach perihelion behind the Sun as seen from SDO. So SDO will only have a relatively brief window in which to see it before it disappears behind the solar limb. However, a group of us met yesterday to discuss this and the SDO team are planning to do some special operations to maximize our chances of observing the comet.
4. PROBA: I was delighted to receive an email from the European "PROBA" team. They have an EUV imager that they plan to try and use to observe the comet. From their message to me,
    "PROBA2 is an ESA microsatellite pointing to the Sun from LEO [Low Earth Orbit]. Onboard is the SWAP EUV imager with a significantly larger FOV than SDO/AIA but imaging only in the 17nm bandpass (see eg http://proba2.oma.be/swap/data/mpg/movies/swap_cr_2116_yellow.mp4 )
    We have made a little movie of how the Lovejoy comet is expected to pass through our FOV. It is available here: http://proba2.nicula.net/lovejoy_predict.mov
    A couple of hours after the event, the data in movie format will appear here and in FITS format here.
    Of course, it remains questionable if we will see anything at all in the 17nm bandpass.
    "
So rest assured that we are trying to make this the most well-observed Kreutz-group comet ever, and are trying to return as much science from it as we possibly can before it is forever lost to the Sun's searing corona! As always, keep checking back on this page as I update it with the latest news about the comet and the observing operations we have planned for it.

Dec 11th, 2011

Last week was busy for me so not as many updates as I'd like to have done. But right now there's not too much more to say about this comet. Ground observations are increasingly challenging, though images are still being obtained from the ground. And the good news is that Comet Lovejoy continues to brighten, with m1=7.7.

This is great news and shows that the comet is still "alive and kicking". At time of discovery there were several parallels drawn between this comet and C/1945 X1 (Du-Toit), due mainly to the location, timing and brightness of this recent comet when compared to Comet Du-Toit. However, this 1945 object never really got all that bright, with mag 7 being the peak magnitude recorded for it, and no sign of it at perihelion. So it is natural to be concerned that Comet Lovejoy could suffer the same fate. We are not "out of the woods" yet, and there is still a chance that Lovejoy will rapidly disintegrate at any moment, and be a huge disappointment in the solar spacecraft. A highly respected astronomer over on the comets-ml site has also raised the excellent point that photometrically (i.e. in terms of brightness), the ground-discovered Kreutz comets behave very differently from those seen by SOHO, the latter brightening dramatically, often by many orders of magnitude, between 20 and 10 solar radii, and then fading dramatically thereafter. Ground-discovered Kreutz follow a far more gentle brightness pattern. Therefore it is not necessarily valid to say that if this comet is mag 7 when it reaches STEREO/SECCHI HI-1, then it will reach mag 0 in SOHO data (this is a typical brightness increase for a large sungrazer seen in SECCHI data). However... and this is just my opinion... I do not think that this is a "typical" ground-discovered Kreutz comet; I think it is a slightly-larger-than-usual SOHO-discovered Kreutz that just happened to be spotted from the ground first. So I stand firmly by my wild speculation that it will reach mag -3 and will NOT survive perihelion in any appreciable form.

Tomorrow, Dec 12, some of our questions will be answered when this comet enters the HI-1 fields of view on both STEREO spacecraft. Note, however, that the only realtime data we have for those spacecraft is very low-resolution. I am requesting access to full-resolution data as soon as is physically possible, which looks like late tomorrow or, more likely, sometime on the 13th. I will post those images as soon as I have them, along with a magnitude estimate and my latest thoughts on this fascinating discovery!

Dec 12th, 2011

1300UT: Today should be an exciting day! Shortly after I posted yesterday's update, I saw the exciting news that Comet Lovejoy was up to m1=6.1 as of Dec 11! The astronomer responsible for that report, Jakob Cerny, also linked to a projected "light curve" (brightness estimate) for the comet. This light curve shows the brightness of the comet going literally off-the-scale. As Jacob did in a later post, I want to urge the utmost caution in trying to interpret that as real. Comets are wildly divergent beasts, particularly when so close to the Sun, and you can not easily apply general rules to them. Once again, I reiterate my m1 = -3 peak-magnitude claim. But the main point of this entry is that this comet is now brighter than Du-Toit (which I talked about yesterday), and seems to be holding itself together quite nicely. We will find out more later today...

1440UT: Last night it became apparent that Comet Lovejoy had entered the STEREO/SECCHI HI-1B field of view, as predicted. I'm not going to post an image yet as it was only visible in the ultra-low resolution "space weather" images, which are images that we use purely for identification of coronal mass ejections (CMEs) and pretty much nothing else. Now, normally it takes us two to three days to get all the full-res data played back from the spacecraft and processed, etc. But the SECCHI operations team is just down the hallway from me so as a favor to me, they are going to try and get me the most recent data as soon as they possibly can... hopefully a few hours from now! So stay tuned to this site and the Sungrazer Twitter Feed and I will post updates throughout the day.

1530UT: The first realtime "playback" image from STEREO/SECCHI HI-1B has been made available to me... and I see the comet! It's kind of obscured by a star right now so will wait for a couple more before posting any images/animations. Hang tight -- they're on their way...

1745UT: Everyone's patience is commendable! Here we have the first full-resolution (cropped and scaled x2) sequence of Comet Lovejoy in the STEREO/SECCHI HI-1B images! My rough by-eye estimates would say it goes from about m7 or 7.5 to near m6 in this sequence. I will need to load it into some different software to get a more precise estimate of that, which is exactly what I intend to do next! I will also upload some of the FITS data images to make them available to everyone to play with.

In the animation you see on the right (click for larger version) you can clearly see the comet heading diagonally through the images. The vertical bar that moves left-to-right is a saturation line from Mercury, which is cropped out of this sequence.

1930UT: Some crude analysis here...

The image to the left (click for larger version) is a very roughly annotated screenshot of the most recent full-resolution FITS image that I have (2011-12-11 16:49UT, 4MB FITS image -- right-click and save!) with some of the brighter surrounding stars labelled. Notice that I'm using the HD (Henry Draper) catalog label for the stars; that's what my software uses. So using the excellent DS9 tool, I looked at the brightness of some of these stars when compared to the comet and found that overall the comet is approximately as bright as the biggest star there, HD 80425, which is cataloged with a brightness of mag 6.6. Therefore, I am content to say that the comet is about mag 6.5 in that image, and that's consistent with my earlier by-eye estimate.

This method of estimating the brightness of the comet is reasonably good to within maybe half an order of magnitude but it is fraught with errors, the two main ones being the brightness gradient in the background (which is quite evident just by looking at the image), and the responsiveness of the camera to different "colors" of stars due to the filter we have on the HI-1 instrument. The first one is taken care of by only looking at stars very close to the comet, but can introduce huge errors if not treated very carefully. The latter is hard to accommodate without calibrating the images, but the margin of uncertainty it puts on the value is certainly less than an order of magnitude.

2000UT: Data! Here are two (rather large) files containing all the full-res data that I have for now. These files are identical in content -- it's merely the wrapping paper that varies. (How seasonal!) I will get more data tomorrow.
I urge you to right-click the above links and choose the "save-as" option. Otherwise the results could be unpredictable based upon your browser/operating system...

Dec 13th, 2011

1400UT: It's almost a little sad when you think about it: Originally as part of a much larger object, Comet Lovejoy has existed for billions of years, since the formation of the solar system. It has outlived countless species on Earth. Indeed, it existed before life on Earth! And now it will almost certainly be completely destroyed within 72hrs. That is a long time spent doing very little, to have such a short remaining time doing so much. But while it may have gone through most of its existence unnoticed, the same can certainly not be said now as increasing numbers of astronomers and enthusiasts alike are following its spectacular demise. For ground-based observers, the comet is now all but lost in the blinding glare of the Sun. But for Sun-watching spacecraft such as SOHO and STEREO, it is an increasingly easy target to view, and that is exactly what we are doing.

Today we should get more images from both STEREO spacecraft, and beginning tomorrow morning it will make its debut into the SOHO/LASCO C3 images. On Thursday it will reach the SECCHI COR-2 cameras, the SOHO/UVCS instrument, SOHO/LASCO C2 and SECCHI COR-1, and finally the EUV images on various spacecraft late Thursday night into Friday morning. As we go through each of these fields of view, I will highlight those and try and post images from each.

Right now though I want to mention the SOHO/UVCS observations. UVCS, or the UltraViolet Coronagraph Spectrometer makes spectroscopic measurements of the Sun's outer atmosphere at 2 - 10 solar radii. It is one of the twelve instruments on SOHO, and it undeservedly doesn't typically get much press. Of great relevance here, for example, are its observations of non-Kreutz comet C/1997 H2 (SOHO) back in May of 1997, where it took the first ever high-resolution spectroscopic observations of HI Lyman beta and gamma emissions from a comet. Among other things, these observations were used to estimate the size of the comet's coma at several heights, and at least a handful of scientific papers were published as a result of these observations. Beginning Late on December 15th, 2011, UVCS plans to turn its gaze towards the track of Comet Lovejoy, with the following observations planned:
TIME (UT)  Height (Rsun)  Pos.Angle   Obs. begin   Obs. end
 17:00         8.37         145         15:00        18:25  Dec 15
 19:00         6.92         140         18:30        19:55
 20:30         5.71         135         20:00        21:25
 22:10         4.14         125         21:30        23:05
 23:50         2.00          99         23:10        02:00  Dec 15/16
The spectral lines in the instrument's range include Lyman alpha, Si II, Si III and C III; observations of these lines could provide invaluable information about the size, dust production and emission of the comet at different stages of its disintegration.

1700UT: As if you needed it, here's proof that I like giving you nice things! Now I have my hands on a bit more data (I'll post it soon, I promise!) I can utilize some of our processing software to produce movies like the one you see opposite (click for larger version). Once again, the comet is obvious, as is that vertical saturation streak from Mercury that's outside of this cropped field of view.

This is a special processing method that we use to reduce the visibility of stars while increasing the visibility of solar outflow (and cloaked UFOs, apparently!). It also happens to be a fantastic way to watch tail dynamics in comets, and here you can already see small scale disruptions in the tail of Comet Lovejoy due to the solar wind flowing over it. If we're lucky enough to get a comet-directed coronal mass ejection, I think there would be a very obvious tail disconnection event.

I'm starting to see a few (perfectly reasonable) questions about why we have relatively little data so far given that we're most of the way through December 13th now. The answer is simply that the STEREO spacecraft are very, very far away and we only have limited contact time with them in order to download the data they take. Right now I think we have two, 5-hour contacts per day. The spacecraft can store a certain amount of data on-board and when we make contact we start grabbing the oldest stuff first and go from there. So this introduces an obvious lag in receiving telemetry. Then once we have it we have to convert it from the data "packet" format the spacecraft gives us into a raw science product, which we store in the FITS formats. We have another contact later today I believe, so I might be able to squeeze out some more data later tonight, but no such promises for that!

1730UT: Here's a direct link to a BIG 103MB zip file containing all the FITS images I have for Dec 12 in STEREO/SECCHI HI-1B. (If that file is too big for you, contact me (sungrazer@nrl.navy.mil) and we'll work something out for getting it to you in smaller chunks.) Once again I recommend the DS9 tool for viewing FITS images but there are several others you can use.

Dec 14th, 2011

1500UT: If comets could feel paranoia, Comet Lovejoy would be starting to get really uncomfortable today as a third camera now has the giant snowball in its sights! As predicted, early this morning C/2011 W3 (Lovejoy) made its debut in the LASCO C3 camera, the most recent image of which is shown opposite (click for full-resolution). Normally for Kreutz-group comets I will crop out part of the image to highlight exactly where the comet is. In this instance, however, I really don't think that's necessary and will instead leave it as an exercise for the reader to scour the image and try to spot the comet...

So now our focus is on LASCO C3, there are some things you will need to know about the images we are taking, and when we expect to see them. First off, we are running an observing campaign on LASCO in which we will be taking images with different exposure times and different colored filters in order to maximize the science return that we can get from the comet. What this means to you, the internet observer, is that you will not see as many "pretty picture" LASCO images online as you normally would, simply because our standard processing routines ignore anything but our nominal (standard) images. Those data files will be available online to download though, of course, and in realtime when available.

The second thing I want to mention is that the spacecraft contact schedule for SOHO is not very nice this week. As I type, we are out of contact until 1600UT, and that pass is only 50-minutes long so we won't get a lot out of that. The next significant contact is a 3hr pass beginning at 2215UT, and then we have a bunch more tomorrow. So the images appearing online will have large data gaps until we get a full data dump tomorrow. The spacecraft is recording all data, though, so unless we get some kind of camera glitch (which happens but is rare) then we should get all of our data down.

Now that's out the way, I want to make a couple of comments about the brightness of this comet, and then I need to go and make more movies. I'll start by saying that this is, without any doubt, the brightest sungrazing comet that SOHO has ever seen. I would say it is the brightest one since C/1979 Q1 (SOLWIND), and I suspect is actually a tad brighter than that one. (Incidentally, it was my coworkers here who discovered that big SOLWIND sungrazer). As it entered LASCO C3, I would say that Comet Lovejoy was probably around magnitude 2 -- quite a bit brighter than I thought it would be. If this comet follows the trend of brightening that is typical of the tiny Kreutz comets that SOHO discovers, then it could increase by up to 8 orders of magnitude! However, I don't think it will brighten by quite that much and right now I'll go with mag -4 as the peak but think it might actually be closer to -3 still.

If Comet Lovejoy gets as bright as mag -4 or -5, there is a tiny but non-zero chance that it could be visible in the sky next to the Sun by simply blocking the Sun out behind a tall building, for example. (Important: Do NOT point a telescope or binoculars at, or near, the Sun! It can and will badly damage your eyesight.) It will be reaching perihelion right around sunset time for people in the US East, Central, Mountain, and Pacific time zones, so if you have one of those nice sunsets where you can actually look right at the Sun, be on the watch for the comet on the left of the Sun (for northern hemisphere observers). If you get any nice pictures, please send them to me at sungrazer@nrl.navy.mil -- I want to make a gallery page for the comet.

1830UT: Here's an updated image of Comet Lovejoy in SECCHI HI-1B (click for larger). Notice the increasing tail dynamics due to the solar wind flowing over the comet.

And now I have time for another data dump! I'm not going to post a link to the LASCO data as that is already easily available in a couple of locations. Here is some more SECCHI data though, which is still harder to find. I'm also going to throw in some processed files as I know some folks aren't used to using DS9 and/or FITS images, and may not have the time or software to process their own. So here's what I have. You would be well-advised to right-click these links to save the files to your computer.
  • STEREO/SECCHI HI-1A Raw FITS, Dec 12-13 (13th is incomplete), 118MB Zip file
  • STEREO/SECCHI HI-1B Raw FITS, Dec 13 (should be complete), 95MB Zip file
  • Processed ("star removed") PNG images, STEREO/SECCHI HI-1A, Dec12-13, 33MB Zip file
  • Processed ("star removed") PNG images, STEREO/SECCHI HI-1B, Dec11-13, 70MB Zip file
There are a multitude of ways in which the HI-1 data can be processed. My personal favorite is the above "star-removal/running difference" method as it really highlights motion in the comet tail and the solar outflow, and so that's what I have gone with. I hope to start getting data from the 14th soon and will play with it and post it as soon as I can. (Remember: it's really hard to get near-realtime data from STEREO because the spacecraft are so far from Earth and we have very limited bandwidth to download through. I'm seriously irritating my coworker by constantly nagging her to playback the latest data for me!)

1900UT: This is too cute: Comet Lovejoy has a friend! Look in the upper-half of the animation opposite, starting at center and moving diagonally up and to the left, perfectly in step with Lovejoy... It's another Kreutz-group comet! (if you can't see it, here's a hint)

As nice as this is, I am not in the least surprised. SOHO's Kreutz-group comets are very "clumpy", for want of a better word. We frequently see them arrive in pairs or sometimes trios, and the big bright ones in particular will often have a companion comet. I suspected we would get at least one with Comet Lovejoy and indeed we do. It's much more typical of the size and brightness of Kreutz comets we see, and offers a wonderful comparison to highlight just how special Comet Lovejoy is.

So what is this new comet called? Is it another "Comet Lovejoy"? Sadly not. It looks to me like it was actually spotted in the LASCO C3 images by seasoned comet hunter Zhijian Xu at Dec 14 2011 11:48:48. So will it be Comet Xu?? No again. It will be Comet SOHO, number 2190-something, I think. Oh, and notice how it's orbit is obviously slightly different from Lovejoy's? That's also something we see all the time; the companion comets are frequently in slightly different orbits. They are obviously closely related though and the smaller one must have fragmented from Lovejoy some significant time ago, and with some slight (non-gravitational) force between them to "push" them apart like this. These kinds of break-ups are theorized to happen decades before they reach the Sun in order for them to have this kind of separation in space, though this process is not well-known or well-understood at all. It one reason that studying these Kreutz comets is so important, as this knowledge can be applied to all comets and solar system bodies, and give a broader understanding of their orbital and physical evolution.

1950UT: Friend of mine, and expert SOHO comet researcher, Dr. Matthew Knight (Lowell Observatory/JHU-APL) has just sent me some of his preliminary photometry calculations for Comet Lovejoy in the LASCO C3 images. They show that Comet Lovejoy was at approximately magnitude 2.0 as of the latest LASCO C3 data available (16:32UT, Dec 14, 2011). I still stand by my mag -3 or -4 prediction for its peak brightness and I still don't think it will survive perihelion for any significant amount of time (maybe an hour or so at most).

This story continues in Chapter 2, "Survival"





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Karl Battams, NRL (2012)

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