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The Great "Birthday Comet" of 2011, Chapter 2: Survival

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 chronicles the latest news relating to this discovery of, build-up to, and appearance of this object in the SOHO and STEREO fields of view. Initially all this information was on one page, but we did not anticipate just how spectacular this event would be. Therefore, we have split it into two chapters: "Inbound", and "Survival". Updates will happen here as news filters in...

(This article is chronological: jump to the bottom of the page for the most recent updates.)



For earlier updates, movies, etc, see Chapter 1 of this story, "Inbound"

Dec 15th, 2011

A LASCO C3 image taken with a "Deep Red" filter. We use these filtered observations to look at the comet in different wavelengths of light. A processed STEREO/SECCHI HI-1A image showing Comet Lovejoy blazing towards the Sun. The comet's tail is clearly interacting with the solar wind with several discontinuities visible. Also, towards the end of the sequence, note Lovejoy's companion comet just above it. This is the same object I talk about in the 1900UT entry, above. This movie is also available as a 68MB Quicktime movie. 1500UT: Welcome to the beginning of the end of Comet Lovejoy's billions of years long journey through space. In less than 10 hours time, the comet will graze some 120,000km above the solar surface, through the several million degree solar corona, and -- in my opinion -- completely evaporate. We have here an exceptionally rare opportunity to observe the complete vaporization of a relatively large comet, and we have approximately 18 instruments on five different satellites that are trying to do just that.

Right now, everyone is rightly focussing on the LASCO C3 images, where Comet Lovejoy is shining brightly at around magnitude -1 (my estimate). It is also starting to show up in the low-resolution versions of the STEREO/SECCHI COR-2 images. Then very shortly from now, the SOHO/UVCS observations will begin. (I discussed these in detail on the 12th, above.) Finally the comet will enter the domain of the EUV and spectroscopic imagers on STEREO, SDO, Hinode and Proba. These observations will be particularly fascinating to me if they work, but unlike the coronagraph images, there is no guarantee that we will actually capture any images of the comet with all of these instruments.

Back in July of this year, Kreutz-group comet C/2011 N3 (SOHO) surprised us all by being clearly visible in five of seven extreme ultraviolet (EUV) channels on the NASA SDO satellite, marking some of the first EUV observations of a comet, and certainly the first ever direct observations of the complete evaporation of a comet in the solar corona. (This will be the subject of an upcoming Science paper.)Comet C/2011 N3 (SOHO) was a pretty big Kreutz-group member by SOHO's standards, but it very small compared to Comet Lovejoy and certainly was not as bright. So it would seem obvious that Lovejoy should be easily visible to SDO this time around. Unfortunately, it's not that simple.

In July, it was fortuitous that the orbit of the Kreutz comets took them between the Sun and the Earth (and hence the SDO spacecraft), and right across the front side of the Sun. Now we are 6-months later and sadly that means that the Kreutz orbit takes the comets hind the Sun and across the rear face of the Sun. Therefore SDO will not be able to view this object right as it reaches perihelion. However, the SDO team have agreed to "off-point" the SDO spacecraft for one hour in order to increase the amount of time for which the comet is in the AIA field of view. Put simply, the off-point means that they will make SDO look very slightly to the 'left' of the Sun, resulting in the Sun being off-center in the images for a while. Hopefully this will be sufficient to make an observation. If not, we do have a plan B... or a STEREO-B, to be exact!

The STEREO spacecraft are a long way from Earth now, staring at the other side of the Sun, and from the perspective of the STEREO-B satellite the comet's path will be very well placed, taking it right across the disk of the Sun as seen by the EUV imagers on STEREO. And to mark this occasion, the STEREO operations team have an observing plan in place to try and capture the comet, albeit not at quite the high resolution that SDO can achieve.

STEREO observations are available in realtime in low-resolution but you will need to wait for a couple of days for the full-res images. SDO are planning to release the best realtime images they can, and will later on be publishing the url for where you can watch their off-point activities live!

1530UT: More data to play with! Here are the FITS images for STEREO/SECCHI HI-1A for Dec 13 and 14 (the latter is incomplete) as a HUGE 182MB Zip file. I have seen loads of different images and movies online that people have been making from the data I'm posting here, and I think that is just wonderful! When you get into image processing, you soon realize it's often closer to art than science, and you can apply an almost infinite number of techniques and colors to the images to highlight different details. So please continue to download and play with these images, and feel free to send me your work! (I would credit you, of course!)

2050UT: Well if there was ever any doubt as to how bright Comet Lovejoy would get, our question is now answered: ridiculously bright, I believe is the scientific term! As reported by SpaceWeather.com, "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."".

When we say "saturation", we mean that the individual pixels in the CCD camera are obtaining too much light and are getting overexposed. The CCDs (Charge-Coupled Device) pixels are like tiny buckets that collect light instead of water, and just like water bucket, when they receive too much light they overflow. But due to the way the CCDs are manufactured, the pixels can only overflow horizontally into their neighboring pixels, and thus when we get a bright object in the field of view, we see the horizontal bars you see dominating the coma of Comet Lovejoy in the LASCO data. To overcome this we do try to reduce our exposure time, and this will work to an extent. But it seems that Lovejoy is just too overwhelmingly bright and consequently we are simply unable to get short enough exposure times to prevent saturation, even in our narrow-band filters. This makes it hard to get completely accurate estimates of the brightness of the comet. But where we have "lost" the LASCO observations, we have gained the SECCHI COR2 images!

Once again my incessant nagging of my coworker pushed her into playing back the COR2 images we took earlier today, and so the result is a nice big set of data, which I have lovingly wrapped up for you all into a big 147MB Zip file! But of course you don't want to have to fight with FITS files when you can have lovely pre-processed PNG images sitting in a slightly smaller 30MB Zip file. But then who wants to make their own movie when you can download a lovely, if somewhat huge, 188MB QuickTime Movie or a somewhat more portable 47MB QuickTime Movie? And for the ultra-impatient among you, here's the most recent, high-res, fully processed STEREO/SECCHI COR2-A image of Comet Lovejoy. And look! No saturation!! [Please, do yourself the favor of right-clicking those links and saving the files locally. Your web browser will thank you later.]

Aren't I nice?! Oh, and within an hour we will have contact again with SOHO. When we get those images, I expect to see C2 dominated by a huge streak, and the comet's head probably just disappearing behind the central occulting disk. They should be very striking images!

Comet Lovejoy in SOHO/LASCO C2 Comet Lovejoy in SOHO/LASCO C3
2250UT: Ugh that wait for SOHO spacecraft contact seemed like forever... It was worth it though! Check these guys out!

There are two noteable things here. First, the comet "turned over" in terms of its brightness. You would expect that a comet that is still two hours from perihelion would just keep getting brighter, right? SOHO doesn't see that, particularly not with the Kreutz-group comets. They peak around 9-12 solar radii away from the Sun and then start to get fainter. So what that says is that this comet is behaving just like a "typical" SOHO Kreutz comet, but on a much grander scale. The peak brightness was probably in the region of -3 to -4 (I totally called that!!), though we will have to confirm that tomorrow.

The second noteable thing for me is that ion tail (the very faint whispy thing you see out to the left). Comets traditionally are known for their two tails: the dust tail casued, literally, by dust and ice pouring off the comet; and ion tail, which is caused by the solar wind streaming over the comet. So why is this noteable? Well, in over 1,600 Kreutz-group comets seen by SOHO/LASCO, this is the very first time we have seen an ion tail in this instrument. I still need to ponder over why that it but my inkling is that the dust tail is very dominant, often hides the ion tail, and the ion tail on Kreutz comet is for some reason either weak or does not show well in the bandpass (wavelength range) of the filters on LASCO. We will study this more!

Now you can follow SOHO for a couple of hours but at 7pm ET you need to hop over to the SDO website and watch their observation attempts "live"! Here's the link for that: http://sdo.gsfc.nasa.gov/data/lovejoy.php

Dec 16th, 2011

1200UT: I don't know where to begin. I simply don't know. What an extraordinary 24hrs! I suppose the first thing to say is this: I was wrong. Wrong, wrong, wrong. And I have never been so happy to be wrong! For the past two weeks I have been saying that Comet Lovejoy would not survive perihelion in "any appreciable form". When I said this, I envisioned that we would see some very diffuse component maybe last a few hours after perhelion, but not much else. I was spectacularly incorrect!

Last night, between 7pm and 8pm (ET), the SDO team blogged and tweeted live the passage of the comet through SDO's extreme ultraviolet AIA camera. Not long after the first images were made available came the announcement that the comet was seen plunging into the solar atmosphere. I expected this, but was nonetheless delighted. What I did not expect was that a short time later it was seen to re-emerge!

Somehow it survived being immersed in the several million-degree solar corona for almost an hour and has now re-emerged back into the views of the LASCO and SECCHI coronagraphs, almost as bright as before! The only noteable exception is that it appears to have lost its tail, as you can see in the image opposite. In fact its tail is still gently floating out in space where it was before perihelion! I think that what we're seeing here is the dust particles following the same path as the comet, but just at a slightly slower speed. So, for example, dust ejected from the comet when it was 10hrs away from perihelion will still follow the same path as the comet, but just reach perihelion much later as it should still have some forward momentum. That "pre-perihelion" tail will gradually dissipate today, but I'm pretty confident that we will see Comet Lovejoy grow a new one. I'm going to work on getting some movies on here now. Stay tuned for another update in an hour or so.

1530UT: Grab your popcorn: I have movies! Click on each for larger versions (anim gifs, so they can be slow to load...)
Here's the comet racing through the LASCO C2 field of view. Notice the faint ion tail: that's the first time we've seen on a Kreutz-comet in LASCO! Here, courtesy of NASA/SDO and the outstanding AIA science team, we see Comet Lovejoy racing through the solar corona, shedding material and (probably) magnetically interacting with the coronal loops. I thought this would be the last we saw of it... I was delightfully wrong! You can also get this movie here as a 2.5MB .mov file This is super-cool! It's from the ESA PROBA2/SWAP instrument! You clearly see the comet enter and leave the field of view. The darkening is due to a (well-timed) "eclipse" where the satellite disappears behind Earth for a short time. I have this as a 10MB .mov file, too. Great work, PROBA team -- you don't get anywhere near as much praise and publicity as you should!

1700UT: I'm going to hope he doesn't mind me doing this, and steal a quote here from highly-respected astronomer John Bortle: "I trust that most here appreciate that we are witnessing one of the most extraordinary events in cometary history."

Let that sink in a minute, because he is absolutely correct. This is not simply "news-worthy", or even "of great interest"; this is indeed competely extraordinary.

Sungrazing comets, particularly those of the Kreutz-group, have fascinated astronomers for decades, and no doubt terrified civilizations of the past, as their orbits hurled them through the solar atmosphere, resulting in a brilliant daytime illumination of these enormous 'dirty snowballs'. There is arguably no other object in the solar system that goes through such an intense experience as one of these comets. For days now we have been witness to such a beautiful object racing through the STEREO, SOHO and now SDO and PROBA images, blasting through the solar corona, and miraculously re-emerging, albeit with much less of a tail than it started with. And whereas sungrazers of the past have been lost at least temporarily, if not permanently, in the Sun's glare, thanks to an amazing fleet of sun-watching spacecraft we have now been enthralled by this entire passage without a single hour passing by unwitnessed. Purely for the spectacle of the event, and the way it has unfolded before our eyes over the internet, this comet has sealed its place in the history books.

But there is so much more to this than just the spectacle. We have already obtained unprecedented scientific data from five different spacecraft, and I'm very optimistic that over the coming days we will get to add a sixth spacecraft to that list when Hinode analyze their data. The result is an almost overwhelming catalog of visual, narrow-band filtered, extreme ultraviolet, and spectroscopic data of a comet experiencing the most extreme environment the solar system has to offer. We will likely learn about its mass, its physical size, its composition, the size of its dust and dust production rates, and so much more. Objects like this can also provide us with a tremendous amount of information about the solar wind and conditions in the solar corona, which in turn allows us to gain more understanding of the Sun as a driver of "Space Weather" at Earth (it's one of the reasons my group is interested in sungrazing comets).

So I could not agree more with John, and I hope that all of you who are watching these movies are indeed appreciative of just how incredible this has been!

Wiggle, wiggle! 1830UT: OK, you get one more movie!

This one is a short animation of four frames from the STEREO-B EUVI instrument at the 171-angstrom wavelength (corresponding to about 1.5million degrees, I believe). The comet is clearly visible racing away from the Sun, leaving a wiggly-tail in its wake! Why the wiggles? We're not sure -- we need to start studying that when we get all of the spacecraft data from STEREO-B this weekend. However, we think there may some kind of helical motion going on, or perhaps there's a projection affect and we're seeing tail material magnetically "clinging" to coronal loops and moving with them. There are other possibilities too, though, and we will certainly investigate those! We should have equivalent images from the STEREO-A spacecraft which we will also get this weekend. When we pair these together, and throw in the SDO images too, we should be able to get an incredibly unique 3-D picture of how this comet is reacting the the intense coronal heat and magnetic loops. We really are going to learn a lot here.

I won't post much here over the weekend (I've already been doing 18-hr days on this) but I will try to get the word out if/when we hear from Hinode. On Monday I will certainly be back with more movies and over-the-weekend updates. I enormously appreciate all the traffic and interest that has been directed at this page and this project. I've tried to keep things fresh and informative, yet informal too. Hope I managed to convey all that (without too many typos, which I do keep finding...)!

Dec 18th, 2011

HINODE SOT image, courtesy JAXA/LMSAL OK, so I said I wasn't going to post this weekend, and I genuinely had no intention of doing so (as it's a pain to do it from home, for one thing) but I have to share this wonderful news: we are six for six with spacecraft observations! The Japanese (JAXA) Hinode spacecraft successfully imaged Comet Lovejoy!

The image you see here is from the "SOT", or Solar Optical Telescope, and if you click to make it bigger you'll clearly see comet Lovejoy sitting in the lower-left corner of the image. In this image, most of what you are seeing is just Lovejoy's nucleus and inner-most part of its coma. Very little tail is observed here, and in fact some of the elongation you can see is due to motion blur as the comet was flying so fast through the images. I also want to add that in the original data, the Sun was massively overexposed in order to enable a detection of Lovejoy, which of course was several orders of magnitude fainter. So the author of this image has inserted an unsaturated image of the Sun, siply to make the image prettier and easier to visually interpret.

This information was sent to me via eamil from the excellent guys over at The Sun Today, so many thanks to them. The Hinode team had to do some very special observations in order to detect Lovejoy, and we a enormously grateful that they did! I stil have not checked in to two other Hinode telescope that hoped to see the comet. I will try to do that today but if not then it will definitely be tomorrow.

Dec 19th, 2011

1400UT: I can't imagine that this week can possibly hold the excitement of last week, but we certainly have some things to look forward to, and who knows what surprises Comet Lovejoy still has for us?

So in terms of things to look forward to, the main thing we're talking about is data. We now know that all six spacecraft -- none of which are cometary missions -- we able to get detections of the comet on at least one of their instruments. We are still waiting for a response from STEREO-A (EUVI), SDO (HMI and EVE), and Hinode (XRT, EIS). In all of these cases we're waiting for the data to be downlinked from their respective spacecraft and then processed into an easily-accessible format. I only work on the STEREO and SOHO missions so I'm not sure when the other missions will have their data ready, but colleagues of mine are also involved in both SDO and Hinode so I plan to start knocking on doors this morning. Later this week I'll put out a list of all the instruments on all the satellites that successfully imaged Lovejoy in some manner or another.

We also still have ongoing observations from space. Lovejoy may have left the LASCO fields of view now but it remains in the STEREO A and B HI-1 fields of view, and in HI-1A in particular, it's looking spectacular! That image I just linked to is a very low-resolution 'real-time' image from STEREO/SECCHI. We use those images for realtime detection of space weather events (coronal mass ejections, etc), so they're not great for comet viewing. They do provide a wonderful preview of what's to come though! I will resume annoying my SECCHI operations colleague and get her to pull that data down as soon as possible. I will certainly make it available as soon as I have it.

If you don't want to wait for those images, fear not, as Lovejoy is now visible again from the ground! And indeed it's actually more visible now than it was before it plunged through the solar atmosphere! (So much for the comet I said would never survive perihelion...) A multitude of ground-based observations of Comet Lovejoy are being reported now, and for the lucky folks in the Southern Hemisphere, this comet is just going to become easier and easier to see.

So what surprised could Lovejoy have for us? It's hard to say as we've already been well off-the-mark in several respects. My prediction a couple of weeks ago of approx mag -3 or -4 peak magnitude was shockingly good (it was luck, I assure you), but I was totally wrong about the survival prospects of this object. We thought the comet was only a couple of hundred meters in diameter, based on its brightness prior to reaching the Sun, giving it no chance of survival. Now we know it has survived, and therefore must be bigger than we thought. The rough guideline is that a comet would need to have a nucleus of about 500m to be able to survive as well as Lovejoy has, so my latest estimate of the (pre-perihelion...) nucleus size would be something on that order. It's going to be much smaller now as the intense solar heating would have taken its toll.

Another surprise was how Lovejoy has both regained and sustained its intense pre-perihelion brightness. As it raced through the solar corona, Lovejoy's extensive dust tail was completely severed, and thereafter gently floated towards the Sun while its head raced one without it. As it re-emerged from perihelion, all that remained was an intense, condensed nucleus that seemed a shadow of its former self. But within just three-and-a-half hours, it underwent a sepctacular resurgence to return to its former glory! I really did not see that coming, nor did I envision that it would become as bright as when it plunged in, that its tail would re-grow so strongly, that its ion tail (the thin one you see here) would strengthen more than ever, and that it would begin to grace the Southerh Hemisphere skies as it is now beginning to do.

What could be left for it now? What does fate hold for Comet Lovejoy? Well, some component of it will survive now to return into its several-hundred year orbit, and indeed I am comforted by the thought that Sun-watchers in a few hundred years will recall these images and this story, and remember all who have played a part in it. But it's not all smooth-sailing for Lovejoy. It has been through the most hostile environment that our solar system offers, comets are low-density objects, and scars don't heal. If Lovejoy has suffered any serious fractures then at any time it could fragment into one or more pieces, and its still close enough to the Sun to evaporate significantly. It is, however, headed out of the "bottom" of the solar system, and does not encounter any planets or major bodies out there (the Kreutz orbit takes it well inside Mercury's orbit) so it has a really good chance to survive and return to our future descendents.

Comet Lovejoy in STEREO/SECCHI EUVI-A = Wow! (Click for an animation.)
1800UT: This is extraordinary! CLICK HERE for a Quicktime .mov movie showing Comet Lovejoy in STEREO/SECCHI's EUVI-A imager's 171-Angstrom wavelength. (I'm working on an animated gif too, and will post that soon. Click the image opposite for an animated gif)

I'll hold while you hit play a few times...

Not bad, huh?! So what's going on there then??! Well clearly we see the tail wiggling again but this time it looks like the entire comet is dancing about in and out of the corona! Of course it's not -- that's an optical illusion facilitated by the way the tail is moving around. If you were to plot the comet head positions you would see they follow a perfect smooth curve. That tail does not though! What seems to be happening -- and this is my very preliminary reaction that could be as accurate as my Lovejoy-will-never-survive prediction -- is that the charge-free dust in the comet tail is being rapidly charged as it leave the comet and is basically "clinging" to, or certainly interacting with, magnetic field lines in the corona... somehow. Throw in some Fairy-dust and there's your explanation!

Later today I should have a movie from EUVI on STEREO-B which was around the back of the Sun at the time, and got to see the entire transit of the comet through the corona! I'll post that when I have it, so keep checking back or follow me via @SungrazerComets on Twitter.

2000UT: Very quick update: Awesome animation of Lovejoy in HI1-A again. Note the amazing ion tail! (That's the thinner one.) The raw FITS files for this movie are available here as a 144MB Zip file.

I may not be able to get much info out tomorrow, but will again on Wednesday. If any amazing movies crop up though, I will certainly get those out.

Dec 21st, 2011

Comet Lovejoy in STEREO/SECCHI COR-1B. Clicking this will take you straight to a ~7MB Quicktime movie. If it doesn't work, right click here and save the movie to your computer. 1630UT: Things are starting to calm down a little now and we can begin the analysis phase of this event. Lovejoy is still in the HI-1 fields of view on both STEREO spacecraft, but it should be leaving those sometime today. It will continue to be visible in STEREO/SECCHI HI-2 for a while yet, but that's a very big field of view, so unfortunately the best of the show is over. Well, from space at least, because as it recedes from our electronic eyes-in-the-sky, it is becoming an increasingly visible object for Earth-based observers. Regrettably this viewing opportunity is limited to those in the Southern Hemisphere, but many of these astronomers and astro-photographers are sharing their images and movies online. Lovejoy should continue to climb in the morning sky for those folks and, despite an apparent fading of its nucleus over the past few days, its tail certainly has the potential to become truly spectacular.

So here's something I hadn't shared with you yet: a view of the comet from STEREO/SECCHI's COR-1 instrument. This is actually a very interesting movie that shows nicely how this object moved. For the 5% of you that haven't done so already (I know why people come here, and it's not just for the narrative...), please go ahead and watch/download the movie opposite.

This is the SECCHI COR-1 (inner coronagraph) image on the STEREO-B satellite. From the perspective of STEREO-B, the comet moved diagonally across the face of the Sun, looped around it, and re-emerged from around the back. The comet is obvious to see as it enters the camera in the lower right. We lose sight of the head of the comet at ~2300UT as it disappears behind the occulting disk. (We superimposed a Sun image on the movie -- this camera doesn't actually see that.) Then at around 0130UT we see the bright tail of the comet appear again in the upper-left of the image and continue to move out. Here's the fun part: this is not the comet itself! Keep watching, and at ~0530UT you'll see the comet -- minus a tail! -- emerge on the right hand side of the central disk and move towards the lower-right of the image, finally exiting at ~10:45UT.

So if the comet re-emerges on the right without its tail, does that mean the bright thing that flew out of the top-left of the image is its tail?? Absolutely! I summarize the situation here. What we're seeing is the comet streaming into our field of view with a vast cloud of dust and ice trailing in its wake. The comet reaches the Sun, loops sharply around it, and head out around the back of the Sun. But the tail material we see has already left the comet and is just going to carry on in a straight line from the time it was ejected, while at the same time be pushed away from the Sun by the radiation pressure from the Sun itself. So we're actually seeing the tail material sweeping out towards us, while the comet races off to do its own thing.

OK, why does Lovejoy not have a tail after it reappears? How did it get torn off? Well it didn't actually get "torn off", as it was never physically connected to begin with, but what likely happened was that the dust and ice produced by the comet was no longer able to follow the comet in its path as the relatively dense and incredibly hot solar corona "captured" (probably instantaneously evaoprated) any dust and ice particles released by Lovejoy's nucleus. As Lovejoy gradually left the intense near-Sun environment, the dust and ice were gradually able to rebuild, now free of whatever impeding factor the solar corona was presenting it. Within a matter of hours it was again sporting a beautiful tail.

The physics of all of this are uncertain and somewhat unknown. We are only just beginning to start unravelling the mystery, and this is going to take many months and many scientists. But be assured that as soon as we publish new results, I will certainly present them here on this site (minus the inevitably indecipherable science jargon that gets used in scientific papers).

Comet Lovejoy in STEREO/SECCHI HI-1A. See below for links to the movie and the individual images. 2000UT: I have received several inquiries this afternoon about Lovejoy in the SECCHI HI-1A data, so that's what I'm going to focus on here. Since proving me completely wrong and surviving its brush with the Sun, Lovejoy has re-emerged back into the HI-1 images looking even brighter and bolder than when it went in. It's visible in the HI-1 instruments on both STEREO spacecraft, but STEREO-A gives us the best view simply because it a little closer to the comet. I have prepared a nice movie of the comet which you can download here as a big 90MB Quicktime movie, or a more reasonable 30MB .wmv file. In both cases, but particularly the latter, you are well-advised to right-click and save the movie locally; playing them directly in the web-browser can have all sorts of random consequences! The image opposite is a screen-grab from the movie. It was hard to balance out the beautiful star scene without over-saturating the brightness in the comet. Note that the small planet is Mercury and the big one Jupiter.

I have collected together the FITS images for the past several days, and you can download those in these rather large zip files. These are the raw data files so you'll need to do some processing to make them pretty. Try, for example, making a single image that is the median or minimum pixel value for all images, and then subtracting that single median/min from each image in the set. That will remove a lot of the haze and the brightness gradient. You can also try shifting each image to co-align the stars and then subtracting them out. If you have the software tools for it, it's tremendous fun!

This will be my last entry again for today but I should be back tomorrow with yet more movies and info!

Dec 27th, 2011

In summary: The Holidays got hold of me and I didn't get chance return as promised to deliver more movies and info. But I think it's perhaps time that I now take my leave of the stage and metaphorically pass on the the icy torch that is the story of the truly spectacular Comet Lovejoy. So I'll conclude here with a recap, and some final thoughts.

Where it all began: the first three images of Comet Lovejoy ever taken. Image courtesy of Terry Lovejoy. December 2nd seems a long time ago now, when I arrived to work to find an inbox of emails chatting excitedly about a newly discovered, albeit tiny and faint, object that might be a Sungrazer (image opposite). I had no concept at the time of the story that would unfold before us, yet something compelled me to uncharacteristically begin this chronology. (I had never done such a blog before, typically limiting myself to one or two news pieces for the site prior to, and following, the arrival of a bright comet.) Despite much of the early skepticism, which included talk of possible evaporation before perihelion, comparisons with the underwhelming performance of sungrazing Comet White in 1945, and urges of caution lest we have yet another Comet Elenin debacle, I continued to stick my neck out and run with the story. I should make it clear here and now that this was not the result of some sagely wisdom on my part, or a Grand Master-like knowledge of the subject that was mine alone; no, it was simply an educated guess coupled with a tremendous amount of finger-crossing!

Luck, it seems, was on everyone's side. By December 11th, Lovejoy was being imaged by several astronomers and its brightness had increased to a reassuring m1=7.7 (reassuring because I was holding fast to my prediction of a m1=-3.0 to -4.0 peak magnitude). And just a few days later, on December 14th, we got our best view yet of Lovejoy as it entered SOHO/LASCO's C3 field of view, sporting a condensed head and bright, thick tail. So, as it raced towards the Sun, I felt a certain sense of satisfaction when its brightness seemed to peak right around the value I predicted (actually closer to m1 = -4, but that was basically what I said!), and now just waited for the unquestionable fate of Comet Lovejoy: complete evaporation! Indeed, just two days prior to this, I had opined on Lovejoy's fate:

"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."


Then came the evening of Dec 15th, 2011, which is one that will live in my memory forever. After 12hrs in my office, I rushed home to watch the inevitable demise of Lovejoy unfold live over the internet, courtesy of NASA/SDO, who were feeding their realtime images to the world. Right on cue, Lovejoy appeared, blazing into the several million-degree corona; a one-way journey that it simply could not survive. But survive it did, and spectacularly so! It did not emerge unscathed, however. Quite the opposite, in fact, as this once giant icy, dust streak was reduced to a tiny-yet-brilliant point of light with no discernible dust or gas tails. But that was not the beginning of the end for Lovejoy -- it was the beginning of a new beginning for it, as it's spectacular resurgence was to demonstrate.

On the morning of Dec 16th, I was proudly forced to declare that I was wrong. Completely wrong! For nearly two weeks I had stated that this comet would not survive perihelion, and at best we'd see maybe a fuzzy remnant survive briefly. I based this assumption on the evidence I was reading, the previous studies done of similar comets, and my own ~8yr experience with Sungrazers. Armed with that knowledge I quite confidently claimed it wouldn't survive, and in a perfect example of the scientific process, Lovejoy proved me incorrect. And such is the beauty of science, when presented with evidence contrary to our current thinking, we embrace that new evidence, incorporate it, and change our views as necessary. Here, the evidence was pretty incontrovertable: the comet clearly survived, and therefore some of my fundamental assumptions (mainly the size of the comet) were clearly incorrect. So now I know different, and the next time one of these comes along I will adjust my predictions accordingly. Side-by-side of Comet Lovejoy and Comet Ikeya-Seki. They could almost be siblings...

I began this 'Lovejoy chronology' partly just to provide a one-stop-shop for Comet Lovejoy-related information, but also to share with readers how a new scientific discovery can play out and evolve, how we as scientists react to that, and what a wonderful voyage of discovery it can be. I hoped that some of my enthusiasm was infectious enough that it may trickle down to a younger generation of scientists somewhere, and indeed I have received emails from a handful of different educators expressing how they plan to use some of the Lovejoy movies and talk to their classes about this Comet (in many ways, those emails made me happier than the comet itself and easily justified the extra hours of my own I put into this). But I digress...

Following it's miraculous survival, of which I gave it a snowball in Hell's chance of managing (sorry -- I've been dying to say that), not only did Lovejoy regenerate its two tails, they became bigger and bolder than ever before! Why? It's going to take lots of study to figure that out, but my personal opinion is that the searing solar corona literally scorched off the crusty outer layers of the comet, exposing new materials to the solar wind that had previously been buried deeply. Probably in several hundred years time, when it returns to the Sun, it will have rebuilt it's hardened exterior again, and will undergo exactly the same process. That's for future generations to find out.

And now, Comet Lovejoy is gracing the Southern Hemisphere skies, and putting on a truly spectacular display. Visually it looks much like its bigger cousin, Ikeya-Seki, as can be seen in the side-by-side image I put together (on the right of the page). This doesn't surprise me -- they originate from the same parent, and thus you'd expect them to have a similar composition and thus appearance. Other large, bright comets (Hale-Bopp, West, Hyakutake, Halley, to name a few) all have very different appearances, and much of this will be due to their different sizes, composition, and "age" (measured in terms of number of visits to the inner solar system). Ikeya-Seki and Lovejoy will have a very similar composition and "age", with size the only differing factor, and I would suspect that Ikeya-Seki wasn't actually all that much bigger than Lovejoy. Thus, in my opinion, they are strikingly similar to one-another.

Rather fittingly, many of the best images of Comet Lovejoy now show a beautiful object hovering over a hazy glow of the Sun, almost as if it is heading off into the sunset. The Sun will never actually set on Lovejoy, but it will become an increasingly distant object for it as the Comet recedes "down" (orientation is relative...) and out of the solar system on the outbound stretch of an 800-900yr journey. When it returns near the end of the millenium, its fate could actually be quite different due to Jupiter -- the other solar system heavy-weight. As Jupiter moves around the solar system, the so-called "barycenter", or gravitational center of the solar system, shifts around slightly but non-negligibly. Depending on where Jupiter is at the time of Lovejoy's return, it could graze much further away from the Sun or... much closer! So after a few billion years of existence, Lovejoy has another several-hundred year reprieve before it gets to roll the dice and take another plunge into the Sun's searing outer atmosphere.

And thus concludes my Comet Lovejoy odyssey, too. As we get science results from it I will certainly write those up, but it will be in a separate article, not this one. On a personal note, I have received many, many emails from people and I have not been able to reply to all of them, and they are now buried in the depths of a well-stuffed inbox! If your question is unanswered, please try again now I have more time and I will try to answer: sungrazer@nrl.navy.mil. Also, many thanks to all the very complimentary emails I've received about this story I've been telling, and that we've all been sharing and experiencing. And I can't wrap this up without one more prediction, so here it goes: I do hereby predict that we will see another large Kreutz Sungrazing object, much like Comet Lovejoy, within the next five years! I have my reasons for thinking that, and can't wait to see if I'm correct!





Credits: All data presented/offered here is free for public use, so you can take it and use it. We ask that for STEREO/SECCHI images you credit "STEREO/SECCHI image courtesy NASA/NRL", and for SOHO/LASCO images you credit "SOHO/LASCO image courtesy NASA/ESA/NRL", or something along those lines. Email sungrazer@nrl.navy.mil if you're not sure.
Karl Battams, NRL (2012)

The Sungrazer project and all associated outreach efforts are support by NASA. Opinions stated above are those of the author alone, acting on behalf on the Sungrazer Project; all images/information are freely available and/or taken from the public domain; and links are not endorsements of those web sites. Contact sungrazer@nrl.navy.mil with enquiries, comments or input.