We are scientists studying Comet ISON and members of NASA's Comet ISON Observing Campaign team. AMA!

What are the chances that ISON will survive its perihelion and we will be able to see it leaving? If you can quantify that.

You will get a different answer from anyone you ask! I recently published a paper with Dr. Kevin Walsh at SwRI (http://lanl.arxiv.org/abs/1309.2288) where we did numerical simulations and concluded it was more likely to survive than disrupt. On the other hand, plenty of astronomers think it will (or already has) broken up. We will know the answer very soon. (MK)

I read through the paper, it was very informative! Thank you!

Glad to hear someone read it :) (MK)

Can you talk a little about what scientists are hoping to learn from ISON, and whether our opportunities to learn certain things depend on the comet's fate? For example, does science benefit more from a pre- (or post-) perihelion break up, or from ISON surviving its trip around the sun intact? Does it matter at all?

Obviously most (or all) of us are hoping that we get a nice show in December for aesthetic reasons, but I'm also interested in the science perspective. And thanks for doing the AMA!

There's a lot to that question. We make spectral measurements of both the gas and the dust to learn what a comet is made of. We make observations/images of the coma and tail to learn more about the overall physical state of a comet: rotation rate, morphology of any jets, and so on. While we are always hopeful that we will see something completely new, much of what we've been seeing for ISON is "normal" for a comet despite the unpredictable behavior as it approaches the Sun.

As for benefitting more from surviving or breaking up, if it survives, we will be hopefully be able to determine if the intense solar heating during perihelion burned off the outer layers and revealed different material deeper in the interior. That could inform us about the way comets are put together. If a lot or all of the material in the comet is vaporized, we could see some of the more "rocky" materials that make up a comet such as iron or silicon. These only vaporize for comets that pass very close to the Sun, so opportunities are rare to make these measurements. Because we have known for so long that ISON is going to pass close to the Sun, we were able to get everything in place to make these kind of measurements. (RJV)

Ron has nicely outlined the main things we can learn about comets from watching ISON. But there's a huge second bonus - we also get to learn about the Sun! Specifically, we can watch the way the comet tail interacts with the solar wind and use that to infer properties of the solar wind. And then, once the comet gets right into the solar atmosphere, we can watch it deposit material into the corona, leaving a temporary trace over magnetic field lines that are invaluable for testing and validating our solar models.

Sungrazing comets are awesome in lots of ways! [KB]

Thanks to both of you for your replies - and for all of your awesome work keeping everyone informed!

My pleasure! (RJV)

What inspired you to study comets?

For me it's more fortuitous. I got a job at the Naval Research Lab in DC doing data processing/analysis for the LASCO instrument on the SOHO satellite. It's a long story I don't have time for here but through that job I got introduced to sungrazers in that instrument, and the rest is history. I do find sungrazers seriously fascinating though. A ball of ice and rock the size of a city block, flying through the Sun's million degree atmosphere at 0.2% of the speed of light... the solar system doesn't get more extreme than that! [KB]

I like studying something that I can talk to my mom about and she understands. (MK)

To give you a more complete answer, I also really like history and find it fascinating that some comet studies rely on observations that are decades or even centuries old. The topic of my thesis was sungrazing comets (hence my interest in ISON) and I heavily cited work from Ikeya-Seki in 1965. I think I even quoted Isaac Newton (he studied the comet of 1680 which was also a sungrazer). (MK)

I've always had a passing interest in comets starting with Halley and then Hale-Bopp and Hyakutake. Seeing a comet with the naked eye, particularly a very nice one like those last two, is just cool. But I got into comets a little by serendipity. I was wrapping up one project and looking for another, and analyzing some ground-based comet data pretty much fell into my lap. That sparked the interest and from there it just took off. Many of the comets we get to observe are "new" as in this is their first trip down into the inner solar system (at least in recorded history). Looking at an object and knowing that anything you measure about it is the first time that's been done is exciting. We have so few really detailed measurements on comets that the science is still in its infancy (yes, comets have been observed for quite some time but the technology has grown by leaps and bounds in the last 20 years or so). It's great to be part of a such a relatively young field. Every day could reveal something new. (RJV)

I got hired by the Deep Impact mission! So I had to learn about comets because I was part of the EPO team. My background though was in Physics and I had been doing informal astronomy education and observing occultations. Now, I think they are really interesting objects and I'm glad to have been part. (EMW)

The fact that comets, as the DNA of our solar system formation, reveal their secrets via their activity.Since each comet is unique, study of comets helps develop a framework to understand their diversity and the role they played in the formation of our solar system. (PYF)

It's 5 am in Romania, i dont't feel like sleeping, and i'm very grateful for the things i've learned since Ison first joined us. Looking forward to buy a telescope now, because i have found a new hobby :)

Get binoculars first. Join your local astronomy club. Visit local observatories and planetariums. Telescopes can be quite expensive. And first time buyers sometimes buy a Mini cooper and expect it to drive like a Ferrari. A small telescope can be very good, but you have to know what targets are best suited for it. I have several large telescopes (!), but what did I bring to Colorado? My Short tube 80 (a small 80mm refractor that looks more like a giant camera lens). (EMW)

Fabulous! Astronomy is a great hobby, particularly for insomniacs [KB]

Even a small telescope can be a lot of fun. Go get one! (RJV)

[deleted]

I believe that ISON will be entering the SOHO field of view literally in the next few minutes.

Karl and I have been studying the STEREO-HI1A images today trying to understand what is going on. It has definitely gotten brighter over the last day or so, so I am hopeful that it hasn't actually broken up yet. We'll know more when we get more data from the STEREO-A spacecraft, and that is dependent on DSN time. (MK)

Here is the latest SOHO image. I'm not totally convinced that the anomaly bottom right of frame is ISON, but I am concerned about the solar event that has just taken place and will be ISON directed.

WOW! That's ISON!!! Seriously!!! And a nice CME blasting out to greet it! If I had gold, I'd give it to you! [KB]

My interpretation / translation of the Sun unleashing a CME at this particular moment: "You cannot pass! I am the servant of the Nuclear Fire, wielder of the Flame of Fusion. Dark ice will not avail you, Flame of ISON! Go back to the Oort Cloud! You shall not pass!!"

I kind of want to put that on a t-shirt! (MK)

Don't give me too much credit, I'm just good at keeping my finger on F5. So, ISON-Directed CME? Are you guys excited yet?

Very excited - in addition to comet science, there is a lot of solar science that is coming out; seeing in real time the interaction of the solar wind and comet is the best view one can get, I believe. (PYF)

Do we know in advance when telescopes like SOHO will have "data gaps" (as appeared to happen in the hours before this latest image, and as happened with one of the other space telescopes the last time a CME threatened), such that we can be confident we'll actually get to see what happens this time?

Yes, DSN schedules are planned in advance. SOHO has a nice schedule for the next few days and we should only have a couple of hours missing here or there. That said - and we had this happen with comet Bradfield in 2004 - sometimes the electronics box on SOHO will crash and that takes time to recover. The satellite was built in the early 90s using mid-80s tech... that it runs at all is nothing short of a miracle!

So we can't predict unexpected malfunctions but we don't anticipate too many gaps with SOHO. For STEREO it's a totally different story, and we only get a few hours per day to dump data, which then takes time to process, etc. So don't expect realtime from that mission. [KB]

I and many other astronomers are posting our results as soon as we have them http://isoncampaign.org/observation-logs. You can keep following along for our newest results. (MK)

Thanks guys. Your work is fantastic.

Thank you! (RJV)

How fast can a comet travel? PS Awesome glasses.

Comet ISON will be traveling at about 380 km/s at it's closest approach to the Sun. That is about as fast as anything can travel in the solar system. (MK)

Further to this, a comet will go faster the closer it gets to a massive object. Comet Lovejoy in 2011 was around 600km/s at peak, I believe. It's harder to get much faster than that as it would mean getting absurdly close to the Sun - and that tends not to end well for the comet. [KB]

What limits that speed?

I can't quickly find a link, but it's based on Newton's laws of gravity. The extreme case is a comet coming from the very edge of the solar system (so semi-major axis is approximately infinity) and coming all the way to the edge of the Sun (0.00465 AU). In that case the equation is V=sqrt(2GM_sun/r) where r is the perihelion distance. ISON's r is a bit bigger than the minimum, but it is darn close. Note that C/2011 W3 Lovejoy came even closer so it was going faster than ISON. (MK)

First I would like to say that whoever was point on coordinating the number of eyes, both in space and on the ground, we have looking at this thing deserves a big x-mass bonus. My question is after perihelion, ISON will be moving out of the ecliptic plane, but I was wondering how close to Earth's orbit it came on it's way in, how much dust or matter it was putting out at that point, and whether we have the possibility of a new meteor shower in late January as a result?

Thanks! We appreciate the praise. I'll stand on my soapbox and say that the members of the CIOC have volunteered our time and spent a ton of nights and weekends creating the content on http://isoncampaign.org/, talking to the press, and trying to facilitate observations by our colleagues. But it's not just us. NASA has supported our efforts and dedicated an unprecedented amount of telescope resources to observing ISON. And we are deeply indebted to all of the professional and (especially) amateur astronomers who have studied it and made their results public over the last year to help us all understand it. ISON really has been a world-wide effort. (MK)

Once everything is said and done, what do you think/hope you might learn from this comet in particular that we didn't know before?

There are some answers to this question spread throughout the comments. In particular see the responses to microwavetowers. (RJV)

These are the responses Ron is referring to [KB]

Hi, just here as a bystander. Awesome info!

Thanks! (PYF)

Thanks! (MK)

Thanks!! (RJV)

Knowing that ISON is basically surrounded in fresh ice, if it gets too close to the Sun, wouldn't the ice boil off and the comet literally fall apart or break up? Would we see a string of pearls like we saw with Shoemaker levy 9? Also why does it takes days for satellites to get data back to us? Why can't data come back to us almost instantaneously like it does with weather satellites? Why is NASA delaying the information to the general public?

Material will certainly "boil off" the comet as it goes by the Sun, and it will do so at a high rate. The comet is also moving very quickly so it will only be very, VERY close to the Sun for a short time. How much material comes off and how fast it does so depend on the actual make-up of the comet and how big it is. Those are still somewhat unknown, though upper limits have been placed on the size.

The reason that spacecraft take time to get the data back to us has to do with the communications system. Satellites in orbit around Earth are close by and can be accessed all the time (or nearly so) by even small radio dishes. Spacecraft far away require much larger radio dishes, such as those as part of NASA's Deep Space Network. But time with those dishes has to be scheduled and not every spacecraft can use them at the same time. There are also periods when spacecraft are "out of contact" so to speak, such as when they are on the other side of the Sun relative to Earth. NASA isn't delaying anything intentionally. We'd all love to have unlimited bandwidth and get our data back ASAP. (RJV)

Thank you for your swift response. By any chance, is there a live feed from SOHO or STEREO-HI1A for us to watch? I'm new at this so please bare with me. I only take pictures of the sky. ;)

Real time images from SOHO are posted here as they come in: http://sohowww.nascom.nasa.gov/data/realtime-images.html

http://sohowww.nascom.nasa.gov/data/realtime/c3/512/

Is that white streak on the right side ISON?

yep! :) [KB]

Yes it is. It literally came in to the C3 field of view as we were doing the AMA! (MK)

I'm currently a senior in high school and I took a college level astronomy class and fell in love. How does the job market look for those who major in astrophysics? Would you recommend it?

To be honest, the job market for astronomy is really tight. Unfortunately funding for the organizations that sponsor astronomy research like NASA and NSF has been cut substantially in the last few years. There are jobs, but it takes a lot of hard work and isn't something I would recommend unless you really love doing astronomy. With that said, I saw a story recently that said that people with astronomy degrees have among the lowest rates of unemployment for any college major. So the skills you acquire when training to be an astronomer are very marketable, but you just might end up doing something other than astronomy with those tools. If astronomy interests you, by all means keep doing it as long as you can, and remember that you don't have to get paid to do cool science. This ISON campaign is proof of that! (MK)

Speaking from my personal experience, I chose to work in academia to continue studying and doing research on topics that I enjoy. As in any field, there are ups and downs in the job market, so it is not an easy question to answer. However, I found that along the way I picked up some great skills (programming, observing, etc.), a lot of knowledge and met interesting people that I am able to engage in a variety of planetary science topics - and this with a background in pure physics to observational planetary sciences. This may not directly answer your question, but you have to enjoy what you do to do a good job. Good luck with school! (PYF)

I think the skill set one learns in an astronomy major is broad enough that you can enter many fields after college, not just astronomy. Besides research, there are a number of educational or outreach career paths. There are downsides. Funding cycles go up and down, so sometimes it's difficult to find work and sometimes it's not. That being said, it's a lot of fun. Whatever you do, though, I recommend a major/career that you love because that is what will make things work out best in the long run. (RJV)

Looks like some controversy is brewing over whether ISON is still intact. How is ISON faring so far, and will it survive perihelion?

It's so incredibly hard to answer this... We're seeing lots of contradictory evidence about the comet. Some of the latest data implies it is now little more than a giant dust ball with little or no coherent structure. But OTOH some of the data that Matthew and I have looked at in particular hint that the comet had another recent outburst of some kind but is now returning to somewhat more "normal" behavior. [KB]

The solar wind at the distances that sun-grazers pass is likely to be much stronger and much more variable than what we see at 1 AU. Is there anything we could look for to specifically look for this solar wind variability effect? As opposed to general solar variability and heating.

The 3-D views of ISON made possible by simultaneous observations by SOHO and both STEREO spacecraft will allow very good measurements of the solar wind over a large range of time and heliocentric distance. In particular, I'd look for changes to the way the tail behaves, but I admit this isn't my specialty.

Also, X-ray observations of comets show the solar wind interacting with the comet. Chandra observed it pre-perihelion when it was close to the ecliptic plane and sampled the hot solar wind. There are post-perihelion observations planned to sample the cold solar wind as well. (MK)

MESSENGER X-ray observations of ISON are still hung up on the spacecraft awaiting DSN time. Anybody got a spare 70-meter dish we can borrow? (RJV)

Hello! Can Europe see comet ISON too? thanks in advance!

Not right now, no -- it's too close to the Sun. But if it survives going past the Sun then yes, absolutely! [KB]

If it survives, ISON will be a northern hemisphere object, so yes, it will be good for European observers! (MK)

Try isonatlas.WordPress.com for charts. (EMW)

I'm so excited to see if ISON will make it. Is it possible that ISON could break up and send debris toward Earth, since it's post perihelion path is directed at Earth?

Good question: If the comet survives it passage around the sun and continues on its post-perihelion path, it will pass close to earth - at which point,depending on the amount of fine dust particles present in the comet's tail, some of the fine material may slowly fall into the upper levels of earth's atmosphere. These fine dust particles would then serve as nucleation sites for water molecules to condense on and give rise to the formation of noctilucent clouds - wispy ethereal clouds. It is difficult to predict when and where these clouds will form, it at all. There is no danger to us on earth. (PYF)

Thanks PYF. I like your answer better than MK's. I love me some noctilucent clouds.

Thanks - then I hope you will send it some pics if they form! (smile) (PYF)

There is no chance that the debris from a breakup would hit the Earth. ISON's path doesn't get close enough for any debris to get here. Space is a big place! (MK)

Do you agree with JPL that the eccentricity for ISON is .9999977109551715 and that therefore ISON has a closed orbit and necessarily will return?

When you're down to that many decimal points, you have to consider what the error bars might be. JPL and the MPC produce orbits in slightly different ways - both equally valid. Depending on how you do the fittting or if you include a certain parameter or maybe include/exclude a certain observation, you can get very small differences. The bottom line with the orbit is that it's ridiculously long and basically take the comet out of the solar system. [KB]

When will we find out if the nucleus is in tact after the sun grazing?

Excellent question. We don't can't say for sure! It depends on exactly what happens. If it breaks up and the fragments separate quickly we may be able to see them individually. This happened for the sungrazing comet Ikeya-Seki in 1965. If it disintegrates like C/2011 W3 Lovejoy, it may be a few weeks before we know for sure. (MK)

As you guys very well know, there's been a ton of speculation about whether ISON will break up over the next few days. What's your take? And if there's no way of knowing, what do you want to happen?

If ISON had broken up a week ago, we would have gotten some great shots with MESSENGER (spacecraft orbiting Mercury). That would have been cool. But as I am a member of several teams hoping to observe ISON at both the Keck Observatory and NASA's IRTF on Mauna Kea post-perihelion, I very much hope that it survives. (RJV)

Although most ground-based observers cannot see the comet, it does show well in the solar spacecraft; therefore, a reasonable guess it that the comet or its tail will reappear post-perihelion. I want to be able to observe it with a beautiful tail so that I can study the scattering properties of its dust.(PYF)

See my response to buckfutter22 for what I predict will happen. What I hope will happen is that it mostly survives perihelion but breaks up into a few pieces. That will hopefully release enough material to produce a really spectacular tail but still give us something to observe. Better yet, we could study each fragment individually and look to see if ISON is homogeneous or heterogeneous on the inside. (MK)

Do you think Ison will survive perihelion? What are the chances i will be visible with the naked eye next week, or after?

There have been so many reports of the comet's demise already that I have to say ISON is the little engine that could just because it keeps on going. The fact that I have 12 days/nights of post-perihelion observing time has nothing to do with this statement. :-) (RJV)

Hopefully all of us will answer this one. Me (Karl), I lean towards "no" now. But two days ago it was "yes", and tomorrow it might be "yes" again! (I'm a scientist - I'm allowed to change my mind!)

If I'm correct and it doesn't survive, we still stand a half-decent chance at seeing something in the night skies. Comet Lovejoy in 2011/2012 completely fell apart at perihelion, and that was a gorgeous comet in the night skies.[KB]

I think the comet will survive perihelion and may reappear, but may not last too long post-perihelion and so am looking forward to a nice display of a tail - but I secretly hope that the comet will linger in our night skies as it continues its journey out of the solar system - ever optimisitc! (PYF)

I'm on record as saying "yes" (http://lanl.arxiv.org/abs/1309.2288) so I'll stick with that. But like Karl said, it's been a roller coaster recently. And like Ron, I have a lot of observations planned for the next few months so I'm really hoping it survives!

Have any of you published any papers on ISON yet? Do you plan on publishing any in the future?

There are a couple of papers in the works that I am involved with, and we will certainly be publishing our MESSENGER observations once we get them all down from the spacecraft and can analyze them. There will also be papers that come out of the Keck Observatory and NASA IRTF campaigns that I was a part of. Most of us are waiting to see if the comet survives perihelion because we have more observing time if it does. (RJV)

Some of us have published papers, and plan to publish more as we complete collecting data and the observing campaign comes to a close. (PYF)

I have a prediction paper out that hopefully proves to be correct! http://lanl.arxiv.org/abs/1309.2288

It is usually a long (many month) process to get a paper published, and most of us are only now getting really good data, so it is pretty early for most papers. We are keep track of the published papers on the CIOC website here: http://isoncampaign.org/Publications (MK)

[deleted]

Bad decisions and poor judgement.

OK, I jest. It's a long-ish story but at a NASA meeting in January, the rep there from HQ suggested that maybe someone organize an observing campaign for the comet. Casey stepped up and then immediately scanned the audience for victimsvolunteers. He asked me (Karl) because I work closely with the solar spacecraft teams that are studying the comet now. But all of us on the CIOC bring something unique to the table with a broad range of experiences and expertise. [KB]

No, you were correct with victims... ;-) (RJV)

Some links for the curious:

• Info from Phil Plait on the Turkey Day Hangout
• Latest SOHO Images
• Latest STEREO Images
• Latest HI STARS Image
• NASA Comet ISON Observing Campaign
• Yahoo Comets Mailing List
• Karl Battams Twitter Feed

Awesome links, thanks! And I appreciate whoever started the #MatthewKnight hashtag. I'm famous! (MK)

As for images, space weather.com has a nice collection. Padma has a Pinterest board of ISON pics. And although I haven't advertised it as much (no funding), there's also the Amateur Observers' Program aop.astro.umd.edu (EMW)

Given that our Oort Cloud is thought to extent 1 light year into space, which is roughly half the distance to the closest star, and that some other stars have had Oort clouds detected around them - Is it possible that much of our neighboring interstellar space is really a "sea" of comet nuclei?

Actually, the closest star is on the order of 4ly.

Interesting idea. And one of many reasons we try to observe comets hoping to one day see one come from outside of the solar system. (EMW)

What are the green glasses for?

Karl and I are at the McMath-Pierce Solar Telescope at Kitt Peak National Observatory in Arizona. This allows us to look much closer to the sun than most optical telescopes. In order to find ISON we have to see it through an eyepiece against a very bright sky. The glasses are to protect our eyes and help with the contrast a bit. (MK)

Plus we look handsome in them [KB]

We were just being filmed by a crew from Discovery Channel (literally as we started this AMA). They had us put some glasses on for a blooper real. I'm not sure you'll see that on their show, however. (MK)

They are doing a blooper reel? Oh no! (RJV)

What is the accepted diameter for ISON right now?

The upper limit is 4 km in diameter based on Hubble observations in the spring (http://adsabs.harvard.edu/abs/2013CBET.3496....1L). We can infer a lower limit of ~1 km based on the published gas production rates. I have heard rumors that the Mars Reconnaissance Orbiter may be able to constrain the size further (closer to the small end), but they haven't published it yet. (MK)

ISON passed Mars in October, why haven't they published the info yet?

It takes a lot of time to get good science. The last thing any scientist wants to do is publish something hastily and make a silly mistake, especially on something as high profile as Comet ISON> In the case of MRO, they used an instrument that is designed to look at the ground of Mars from relative close and managed to see a tiny comet zooming by a long way off. The fact that they got data at all was amazing, so it's taking a lot of work to be sure of their answer. (MK)

The same is true for MESSENGER. The spacecraft and instruments were designed to study Mercury, not comets. But we got data on ISON -- and as a bonus on 2P/Encke too! -- but we first have to wait to get all our data down and then we have to analyze it. The processing routines we developed for Mercury data just don't work the same way on comet data, so it's going to take a little while to work it all out. But eventually you'll see our observations hit the street. In the meantime, you can see a couple of images at http://messenger.jhuapl.edu (RJV)

Where can members of the general public go to see ISON or find information on how to locate it themselves?

Great question, and hopefully one that Elizabeth or Padma can answer better than I can. Many astronomy clubs and science museums around the world will likely be holding events. I suggest reading your local paper for tips on when and where to try to see it. I happen to be located on a mountain at an observatory so hopefully I'll have a great view! (MK)

Charts: try isonatlas.WordPress.com (EMW)

There are many websites that provide information on how to observe the comet in your local area. There may be various activities in your area - check with the local schools, planetaria, amateur astronomy clubs - maybe Elizabeth has more ideas. (PYF)

I just want to start off by saying thank you for all of your work. I think that understanding comets plays a big role in understanding the origins of the universe.

My question is, what is your favorite space oriented phone app? I am always looking for the newest and best.

Awesome question, but I have to confess that I don't have a smart phone. I am very jealous of the people with apps that you just hold up in the sky and it tells you what you're looking at. (MK)

Sorry: I don't have a smart phone and don't know how to use apps. (PYF)

Sigh. I recently saw my cell phone in a movie from about 10 years ago...or was it 15? (RJV)

Part of me expected this and part of me expected a pm with an invitation to a super secret comet tracking app.

We have that, we just don't tell anyone about it ;) (MK)

Well, I do have a smartphone... And since I work at the campus observatory, felt it was my duty to download any/all spaceapps! And then I rarely use them. So, I have them sorted by type. Sky Safari (I have pro) is a great planetarium program and has lots of features. I have Jovian widget and Galilean Moons which are great for observing Jupiter... Several different satellite apps... And of course, ISON Finder. I have a Droid so not sure which are also available on iPhone.

On my iPad, I have some other apps like ThevPhotographers Ephemeris... But there are lots to chose from! EMW

Hadn't seen sky safari, thanks!

I am interested in the fact that the others aren't using smartphones. Is there a particular reason? I only ask because I am posting this on a device that is nowhere near a computer, but instead is bouncing a signal across the earth and space. I figure that would be right up your alley.

I'm as surprised as you are! I have had no cell reception and no wifi since I got to Kitt Peak and my Droid sits lonely and switched off in my room. I'm suffering major withdrawal! [KB]

This question is for Matthew: What about magnetic fields???

I'm not Matthew but I do have some expertise on Solar System magnetic fields so I'll chime in. Comets generally won't intrinsically have magnetic fields. Geophysical magnetic fields are generally produced by electrically susceptible material (e.g. liquid iron) moving around in the core of the object. However, as the comet's coma becomes ionized by the solar wind, the cometary ions will start to move and create their own magnetic fields. In this way, comets have what can be called induced magnetospheres (as opposed to the intrinsic magnetosphere that something like the Earth has).

Is this MAVEN crashing the party? :-)

Carlita! We're hoping that ISON will be seen by Solar Dynamics Observatory (see their blog about it here: http://sdoisgo.blogspot.com/2013/11/the-perihelion-passage-of-comet-ison.html). ISON's behavior when observed by SDO should allow solar scientists to learn a lot about the Sun's magnetic fields, corona density, etc. (MK)

To see the comet ISON, what direction in the sky I have to see? I am from India

We've answered this elsewhere, but look towards the east before sunrise in early December. (MK)

Will ison be best visible in the morning or during sunset?

We've answered this elsewhere, but the best time is likely to be in early December 30 min or so before sunrise. (MK)

[deleted]

Absolutely not, and absolutely nothing except hopefully a really nice object for the astronauts to see out their window!

If ISON performs well, the astronauts on the ISS might have the best possible view. Check out this video one of them made of the sungrazing comet C/2011 W3 Lovejoy: http://www.youtube.com/watch?v=aoZIwtgEqKY (MK)

Good to hear. I heard that some estimates said it's possible it'll be brighter than the moon, likely?

Not at this point. Early estimates were... Overly optimistic. (EMW)

Hi there! Thanks for taking the time to answer questions!

Where exactly in the sky will ISON be on Christmas night in North America?

Assuming C/ISON reappears post-perihelion, it will be visible before dawn and after dusk, close to the Big Dipper (PYF)

Do you guys think that ISON will be consumed by the sun, or not? And how likely is it that you think we'll see the comet?

There are a lot of responses to similar questions spread throughout the comments. Browse around to get a variety of opinions. As for seeing the comet, lots of people are already seeing it with the naked or binocular-aided eye according to reports. Get up early and give it a try if you are in a region with a shot at it. If you mean see it after perihelion, that's also been answered in comments with various opinions. (RJV)

Based on data from past sungrazing comets, it seems like comets smaller than ~400 m in diameter will lose all of their mass due to sublimation, in other words "be consumed by the sun." The best estimates of ISON's size suggest it is about 1-4 km in diameter (see my answer to Garrettishere), so it should be big enough to survive that. However, there is still the chance it could break up for other reasons and not survive. I'm hopeful that we'll see it after perihelion, but wouldn't want to put odds on exactly how likely that is. (MK)

Hello from Greece, I wanted to know what ISON & ENCKE means about our ordinary life? I mean, is there any effects to earth? (weather..etc.)

Neither ISON nor Encke is likely to have any effect on Earth. However, Encke has produced some harmless meteor showers on Earth (http://en.wikipedia.org/wiki/Comet_Encke#Meteor_showers) (MK)

Good question. Although the ordinary person's daily life might not be impacted nor influenced by the presence of a comet (unless he/she is a comet scientist), the question of how water and other materials were delivered to earth to make it habitable is not completely answered. Can comets deliver these ingredients for life? However, there is a lot of diversity with the comets observed. Therefore, studying and characterizing as many comets as possible helps in providing information about their sources and and how life may come about. (PYF)

Any plans to view the comet from Earth-based solar observatories at perihelion?

This is, in fact, what Matthew and Karl are doing right now at the McMath telescope on Kitt Peak (observing ISON as it goes toward and, hopefully, comes back out from the Sun). There is another team at the Dunn telescope in New Mexico. I think at the very instant of perihelion ISON will be "behind" the Sun relative to Earth, so we won't get a direct view from Earth, but one of the STEREO spacecraft has such a direct view I think. (RJV)

A small correction to Ron's answer. ISON will not pass behind the Sun as viewed from Earth. Here's a list of the views from the various telescopes on SOHO and STEREO: http://stereo-ssc.nascom.nasa.gov/comet_ison/. SOHO is directly between the Earth and the Sun, so the view showing SOHO C2 and C3 is roughly what we could see if we could look safely that close to the Sun. (MK)

hey! how far south could the comet be visible if it survives? (and by south i mean southern hemisphere)

It depends on when you want to see it and how far south you are. Early in December most everyone will be able to see it, but by late December it will be essentially over the north pole so no one in the southern hemisphere will be able to see it. (MK)

Particulary i was thinking southern tropic (23°-ish), i'll be in the Atacama Desert, near the ESO Observatories. Full spring, and weather conditions have been good lately. Some really clear skies. It seems like a good prospect!

Should be able to use JPL's Horizon service to generate can ephemeris (coordinates) for your location. (EMW)

If ISON survives its encounter with the sun, will it be visible on its way out of the solar system?

We sure hope so. I and many others have observations planned on throughout the first half of 2014 (which is as far out as telescope time has been allocated yet). We're really interested in seeing how ISON might be different after it's close approach to the Sun as compared to it's behavior on the way in, so there's a lot more cool science left. If it survives! (MK)

If it survives, it will most likely be observable on the way out. It is possible that it could lose enough material that what comes back out is very small and difficult to see, but if it stays intact, I expect that we'll get plenty of decent observations on it.

If it does not survive, we may still be able to see remnants of the comet. The smaller the bits and pieces, the more difficult that will be. If it entirely breaks up, an extended dust trail may be visible, or we could see nothing. There are really a lot of possibilities for what may or may not re-emerge from the perihelion passage. (RJV)

Dude dude dude dude! I am SO stoked about this comet!

Alright, dumb questions here we go! So yesterday around 18:00 (UTC-06:00) I'm walking around the street, you know chillin' and I look up! And I see this BIG BIG shiny star! (Notice that the criteria for big big shiny stars in Mexico City might not be as impressive as you might think but whatev) So I stare at it for around 10 min, it was SO nice and I thought... "could THAT be the comet? NO way, they never said it would look so big, I wonder what that is if it's not the comet" SO... Obligatory shitty PIC: http://i.imgur.com/GRqaHr9.jpg

To be honest the photo does not do any good to whatever I was watching but it was very nice, so is there ANY chance that what I was seeing yesterday was in fact the comet? I went out looking for it around 8-9 pm but it was gone!

EDIT: Grammar! Yes, in Mexico City you can barely see any stars and almost anything I get to see clearly gets me very excited.

Although itcwould be awesome if ISON were that bright, it is Venus which has been quite visible in the evening sky. ISON is in the morning sky until about mid-Dec. EMW

Do you think it should have been named Comet Nevski-Novichonok after its discoverers?

There are a number of large sky surveys that are doing most of the comet discovery nowadays, with the detections being mostly automated. That makes naming the comets after the survey the most reasonable way to do it. I don't know if that was the specific case with ISON, though that is a network of observers and could fit that bill. There are still the dedicated individuals out there that get comets named after them, but I think that day is fading fast. Get out there now if you want to discover Comet Garrettishere! (RJV)

No, #ISON is a much nicer hashtag. [KB]

Comet naming is dictated by the International Astronomical Union's rules, so I defer to them on this. But as someone who has given a lot of talks on Comet ISON, I am glad I only have to say "ISON" and not "Nevski-Novichonok" (MK)

We do have quite a few challenging comet names. A few off the top of my head: 45P/Honda-Mrkos-Pajdusakova, 26P/Grigg–Skjellerup, and 67P/Churyumov–Gerasimenko. Then again, if I grew up in a different country I suspect a lot of those names would be easy to say! (MK)

Of course, astronomers pretty much refer to these as 45P (or HMP), 26P, and 67P, so we've gotten around the tongue-twisty names. (RJV)

When will comet ISON first be visible to northern hemisphere observers post-perihelion?

As soon as it's far enough away from the sun for people to see it. People in dark skies and with good eyes will see it sooner than people in cities. (MK)

What do you think about Brian being killed off of Family Guy?

WHAT??? Nooooo! You just spoiled Family Guy for me! [KB]

Tragic. The banter between Stewie and Brian was half the show, easy. (RJV)

I know! I can't believe they would do that! Sigh [KB]

How much did it cost to observe, research, and pinpoint when it is viewable? Also where will it most likely be viewable?

It's impossible to quantify the cost to understand ISON. It has been a massive undertaking by professionals and amateurs around the world for over a year. It's also been observed by more space telescopes than any other comet in history (I think). (MK)

If it survives (and it will) why you all say that it will never return? Don't they all have an eliptical orbit?

The orbit is so elliptical that if it is closed, then the next time this comet returns to the inner solar system, will be so far in the future, that it might as well be never for us. But the orbit is such an extreme ellipse that it is not clear if if the comwtvwill loop back around or just fly out of the solar system. EMW

Good question. They do have elliptical orbits, but they are also perturbed by their interactions with the planets, asteroids, etc. In ISON's case, it was only very loosely bound to the Sun to begin with, and due to perturbations by the planets may be kicked out of the solar system. I think that the most recent orbits from JPL and the MPC put it right on the edge of being ejected or not. Phil Plaitt just wrote a great article about this in the last day or so. If someone else has the link please post it while I go answer more questions :) (MK)

Are there any high res spectra of ISON right now? All I could find was this...

I have seen a few incredible spectra from the amateur community, but haven't seen any published high res spectra from professional telescopes yet. Like I mentioned elsewhere, it takes a while for data to be reduced and analyzed, and for a paper to be published, so you'll have to wait a while to see more spectra. It will be really cool to see the spectrum change with heliocentric distance. Karl and I are currently at the McMath-Pierce Solar Telescope at Kitt Peak National Observatory (in Arizona) trying to see metal lines that can only ever be seen in sungrazers since they get so hot. (MK)

There are a lot of high-resolution spectra out there, but it takes time to do the analysis correctly and scientists are working hard at it. We generally wait until the analysis is complete before showing the results. It can be a bad thing for your career to release poorly calibrated data just to grab some press. What's impressive to me is that amateurs can make spectral measurements today that only scientists could make not that long ago. (RJV)

Now that we can see ISON in the SOHO LASCO C3 image - is ISON tracking where and at the speed that you expected it to? Does this image help with tracking ISON more accurately?

Yes... But of course since the comet has jets and is releasing material, there are minute changes. Being able to continually monitor the comet helps. I'm really hoping Karl or Matthew jump in... A version of this question was answered earlier. (EMW)

There has been some discussion amongst professionals with very sensitive telescopes that the position may be a bit off recently, potentially due to either fragmentation or outgassing. However, the pixel sizes of SOHO (and STEREO) images are much too large to tell. (MK)

If it does survive the pass with the sun and goes to a magnitude of about Venus, as some predictions say, how long would we be able to see it with the naked eye in the sky at night?

Hard to predict, but for a couple of weeks. Let's hope that it survives perihelion, gets that bright, so that the public can also see it. (EMW)

Why did ISON experience bow shock (assuming it did) while other comets never exhibit this feature?

I think you're talking about the "wings" that were reported. We have seen other examples of comets that showed these [KB]

Looking past days on youtube for more infos (bad ideea, i know) and i found that Ison is actually Nibiru and carrying some UFO's :)) Crazy people out there. How far in the solar system can a comet be first spotted? I'm thinking Ison has some brothers or sisters following it :)

How far out a comet can first be spotted depends on how big it is and/or how much it is outgassing. And whether or not someone is looking in that direction. Often, a comet will be discovered at some distance from the Sun but found at farther distances once astronomers go back and look at earlier data more carefully. This happened for Hale-Bopp, which was discovered around 7 AU but was found in earlier data as far out as 13 AU. (RJV)