New Comet C/2012 S1 (ISON) Could Be Spectacular Sight In Fall 2013

Comet C/2012 S1 ISON was discovered on Sept. 21 in pictures taken with 15.7-inch reflecting telescope of the International Scientific Optical Network (ISON) in Russia. This photo was taken on Sept. 22. Credit: Ernesto Guido, Giovanni Sostero and Nick Howes

A new comet was discovered inching across Cancer the Crab in the morning sky may knock your socks off next fall. Based on a preliminary orbit, it could become a very bright object beginning in November 2013 for both northern and southern hemisphere sky watchers. C/2012 S1 (ISON), its formal name, was found by Russian amateurs Vitali Nevski and Artyom Novichonok of the International Scientific Optical Network (ISON), a network of observers who track man-made space debris.

When first photographed on Sept. 21 the comet was an incredibly faint 18.8 magnitude and appeared much like a star with only a “whiff” of a coma around its icy nucleus. It will slowly cruise through the constellation Gemini for many months while growing gradually brighter. And I do mean gradually. Even as late as next June, ISON will only shine at 14th magnitude; that’s scraping the bottom of the bucket for most amateur telescopes.

The situation improves next September when 8-10 inch scopes should pick it up as a small blob in Cancer around 11.5 magnitude. From late October through late-November, things get much cheerier with C/2012 S1 brightening sharply from 7th to 1st magnitude in the eastern sky at dawn. I’m sure I’ll be setting my alarm for a look Thanksgiving morning.

The sharply curving path of Comet C/2012 S1 (ISON) shown from mid-November through mid-December 2013. The comet will be only 1.1 million miles from the sun on Nov. 29. That’s only a little more one sun-diameter. Maps created with Chris Marriott’s SkyMap software

When closest to the sun at perihelion on Nov. 29 it’s predicted to shine a spectacular -7 magnitude or almost 10 times brighter than Venus. Before you say WOW, you need to know the comet will lie only 4.4 degrees north of the sun (very close!) on that date and probably be hidden in the solar glare. Then again, we might spy it in daylight through binoculars by taking proper precautions to keep the sun out of the field of view. Some of us saw the last daylight comet C/2006 P1 McNaught in January 2007 this way.

The comet will be visible low in the southwest just after sunset in bright twilight with an upward pointing tail. The numbers are its brightness or magnitude. For reference, Venus is -4.4, Vega is 0 and the Big Dipper stars are +2 or second magnitude.

A second round of excellent visibility commences immediately after perihelion as S1/ISON performs a  hairpin turn around the sun and banks north into Ophiuchus and Hercules in early December.

While the comet fades during this time, it’s likely to have a spectacular tail and be as bright as magnitude -4. Both hemispheres will get great views, with the northern favored as Christmas approaches. Indeed, northerners will see it at both dusk and dawn. The comet will pass nearest Earth at a distance of about 37 million miles in January 2014. On the 8th it will appear only 2 degrees from the North Star.

That makes two potentially bright comets in 2013 – the other is C/2011 L4 PANSTARRS. It’s forecast to shine as brightly as Vega next March. While I like what I see, it’s important to remember that comets don’t always perform as expected. Any prediction of a comet’s brightness is subject to change, sometimes radically. I’ve seen a few wax much brighter than expected, while others have gone nowhere but downhill. More needs to be known about C/2012 S1’s orbit before an accurate forecast can be made. Let’s just say things look very promising for now.

The Great Comet of 1680 over Rotterdam painted by Lieve Verschuier. Notice the lack of city lights. Some of the people are using cross-staffs to measure the comet’s altitude and tail length.

One other interesting tidbit about C/2012 S1 (ISON) is that its orbit appears very similar to the Great Comet of 1680 also known as Kirch’s or Newton’s Comet. The two may even be related. Kirch’s comet was discovered on November 14, 1680 by German astronomer Gottfried Kirch.  After passing extremely close to the sun, it brightened so much it was plainly visible to the naked eye in mid-afternoon in early December.

One eyewitness report described it as having a “very fiery tail” that stretched 70 degrees long or more than 2/3 the way from horizon to zenith. Newton was working on his great treatise “Principia” at the time and used the comet’s motions to test the predictions of his theory of gravity.

Will C/2012 S1 (ISON) become a Great Comet, too? I’ll look into my crystal ball when more data becomes available.

64 Responses

    1. astrobob

      Hi Lynn,
      No danger here. The comet will be much too far from Earth. The concern is whether we’ll have enough clear nights to enjoy the spectacle.

      1. Brandon

        I think deflection to public questions only prove why NASA hides the truth, why didn’t you inform the young lady that Earth will definitely pass through the million mile long debris field of the comet, causing a “RAIN OF FIRE” to shower the Earth causing mass death and panic.

  1. Vklotz

    This comet could be the return of the “Star of Bethlehem” with a long tail.
    See the Great Comet of 1680
    Calculate: 2013-1680=333. Then 333×6=1998. Then 2013-1998=15ad.
    There was a census in 14 ad Jerusalem by Caesar Augustus.
    The exact year of the birth of Jesus has not been precisely determined.

    1. astrobob

      Very tempting thought, but unlikely. Because the orbits of the two comets are similar doesn’t necessarily mean that the 1680 comet is the same as C/2012 S1 (ISON). It’s more likely a fragment of that comet. The orbital period of the 1680 comet is somewhere around 9,000-10,000 years, so the last time it was near Earth was long before the birth of Christ. Whatever the case might be, we’ll know more about ISON’s orbit in the coming weeks as astronomers refine its orbit. Then we’ll have an idea of the last time it whizzed by. Another thing to remember is that each time a comet swings by Earth – even the same comet – things like where the Earth is in relation to the sun and comet can make a huge difference in a comet’s appearance. Swingbys of the same comet can be spectacular, other times the comet is only so-so. Such fickle creatures.

    2. Bob Crozier

      King Herod died probably in 4 BC, but maybe as late as 2 BC. So Jesus was born some time before that. The Magi came a fair while after Jesus was born and probably as much 2 years after he was born (see Mt. 2). So the latest reasonable date for Jesus’ birth is 4 BC, and more likely 6 BC. It was actually probably even a little earlier than than these dates depending o how long they stayed in Egypt before Herod died.

  2. Vklotz

    Thanks Bob for your quick reply.
    Do you know of another Comet that appeared about 14 AD that appeared in the East and led the Magi West?

    1. astrobob

      Halley’s Comet appeared in 12 BC. There may have been others, too, but that’s the one on my fingertips at the moment.

    1. astrobob

      Some of us are hoping it will be named after the discoverers Artyom Novichonok and Vitali Nevski rather than the program (ISON) they participate in. I’d love to hear the name Comet Novichonok-Nevski!

  3. Tyler

    Any update on this comet, so excited. BTW, follow your blog religiously from Las Vegas, NV. And also, is there ANY chance it could create a new meteor shower??? please say yes! From it’s orbit, it looks like we won’t be passing though it’s path of debris or is it only short period comets that can create a reliable meteor shower. Keep up the good work!

    1. astrobob

      Hi Tyler,
      Thanks! Glad you enjoy the blog. At least one amateur astronomer has noted that if C/2012 S1 ISON is a large comet, Earth could possibly pass through some of its dust in mid-January 2014. This is not confirmed however.

      1. Bob Crozier

        Do you have any further update on the potential for a mid-January (2014) meteor shower from this comet yet? From the JPL orbit diagram (;orb=1;cov=0;log=0;cad=0#orb), on its incoming journey, it looks like this comet will pass quite close to the orbital path of earth (just to our north), then dropping below the plane of our orbit about half way between us and Venus. I don’t know how close we have to be to the actual path of a comet in order to encounter a meteor shower, but it seems like that should be getting there. How close is Earth’s orbit to some of the other comets that have now caused our several annual meteor showers?

        1. astrobob

          Hi Bob,
          I’ve heard nothing more about Comet ISON and a potential shower except for the bit I’ve reported already. As for the other major annual showers, we pass through debris that’s spread out along those comets’ orbits. The dust-band widths vary depending on how broadly the debris is spread out. Since we encounter meteoroids during each shower, we’re passing either directly through a comet’s orbit or very close (in the spread of debris).

          1. Bob Crozier

            So, does that mean that all of the debris from a comet stays in a pretty tight path right along where the comet actually traveled then? I guess that would also mean that all of those comets that have caused our meteor showers are or were high (significant?) potentials for earth impact?

          2. astrobob

            Great questions. My understanding, based on seeing diagrams of meteoroid debris shed by comets, is that the streams spread out and can become rather broad. Earth may not intersect the most recent orbital path of a meteor-shower producing comet, but once the stream of debris broadens, we can and do cross into it and see a shower. Unfortunately I can’t find any statistics on stream widths. I only know that they evolve rapidly, so that with the Perseids, for instance, it only takes about 8 orbits for outbursting material from Comet Swift-Tuttle to fill out the entire orbit with meteoroid particles. I hadn’t thought about potential for Earth impact, but it’s true that Swift-Tuttle is a possible threat in the distant future. The orbit of the Leonid’s parent comet 55P/Tempel-Tuttle does intersect Earth’s orbit, which is why we get a great shower every 33 years – the dust hasn’t had time to spread and thin. I invite others to add their thoughts to this discussion.

          3. Bob Crozier

            This question is actually in response to your reply below, but there is no link to be able to reply to that comment. The Quadrantid (sp?) meteor shower we just had is a very narrow band of debris or so I assume since the shower is very brief (or maybe we just catch the edge of it?). Does that mean it is from a very recent comet or one that went past only once?

          4. astrobob

            The Quadrantids has been linked to an asteroid rather than a comet. I don’t think anyone knows whether the asteroids shed bits of itself on its own or whether another object collided with it, liberating the debris that now constitutes the shower. I could only guess as to why the peak is brief. The stream might not very wide due to a young age or it may have to do with how we encounter the debris. The Earth passes nearly perpendicularly through the Quadrantids, so we’re “in” and then “out” again quickly. Perhaps even a combination of those factors.

    1. astrobob

      Hi Ira,
      Yes the comet will pass near Mars in early October 2013 at a distance of 6.5 million miles (a long ways off). At the time it will probably still not be visible with the naked eye but a small telescope should show it. When that time comes, I’ll be providing a map on how to find the comet. The reason I don’t concentrate on the Mars encounter is because the best views of C/2012 S1 ISON will come later in the year when it’s close enough to Earth for a great show. Granted, the Mars rovers may get a nice view, but my blog’s written for (mostly) earthlings.

      1. Umby

        The comet will be 6.5 million miles from the earth or mars? Either way that seems very close (less than .1 au). Is it possible for mars to peturb its orbit?

        1. astrobob

          Hi Umby,
          Yes, it will pass 6.7 million miles from Mars in October. That’s actually quite far away, especially given Mars’ small size. While the comet will certainly be touched by Mars’ gravity, its orbit won’t change in any significant way.

          1. Umby

            thanks Astrobob. Do you subscribe to the “Nemesis” theory of a dark body in a binary orbit with our sun stirring up comets and asteroids every 26 milion years?

          2. Umby

            Assuming the CMB as an inertial frame of reference, I would think we’d see red or blue shift relative to it if something was whizzing around the solar system.
            Wouldn’t we?

          3. astrobob

            We don’t usually measure an object’s speed relative to the CMB but you’re correct in principle. Problem is, there’s nothing to measure, since no object matching that description has been found to date.

          4. Umby

            What about the movement of our galaxy “away” from the Big Bang? Would it moving relative to the CMB? I guess my underlying assumption is that CMB is static in size, at some incredible, yet finite, distance out there; and most importantly is not moving. Is this a wrong assupmtion?

          5. astrobob

            Our galaxy has its own peculiar motion within the Local Group of galaxies, which in turn moves relative to the Virgo supercluster of galaxies. The supercluster moves relative to other superclusters which move relative to the CMB, the largest frame of reference we know of. So no, the Milky Way is not moving away from the Big Bang but rather in all these directions which add up to some total relative to the CMB, which is literally everywhere.

          6. Umby

            I’ll try this question one more time then I’ll promise to leave you alone!
            If the Celestial Equator line of declination makes a 48 degree angle with my western horizon, does the +35 degree line of declination also make a 48 degree angle with my (north) western horizon? Yes or no

        2. Umby

          Hi Bob,
          I have a couple of questions regarding lines of Declination intersecting my local horizon.
          1. Does the Celestial Equator (zero degrees Dec.) always intersect my horizon exactly east and west (Azm. 90 and 270 deg.) of my location regardless of my latitude and time of year?
          2. I am at 42 degrees north latitude: What line of declination has the highest (inside) angle with my horizon and why? This will help settle an argument…thanks.

          1. astrobob

            About the celestial equator – yes, it always meets the horizon at the due east and west points. At 42 degrees north, the celestial equator is 48 degrees high where it intersects the meridian. That leaves 42 degrees between the equator and the zenith. A star with a declination of +42 degrees will pass through the zenith – this would be the greatest angle to the horizon a star could make at your latitude. It’s easy to remember – not only is the North Star the same height above the northern horizon as your latitude, but the declination of a star passing through the zenith will likewise be the same as your latitude. Does this answer your question?

          2. Umby

            The question I’m trying to ask is really about my western horizon and the lines of declinaiton. You answered part of it by eluding to the fact the celestial equator would make a 42 degree angle with my western horizon. And I know all lines of declination are parallel. But would all of the other lines of declination, above and below the celestial equator, make the same 42 degree angle with my western horizon? I know starting at +48 degrees declination and greater would not intersect my western horizon as they would be circumpolar, but what about say +45 dec, would it make the same 42 degree angle as the C.E.?

          3. astrobob

            The declination circles below 48 would touch the horizon at different points, not at the east-west points like the equator. The -20 declination circle would intersect the horizon 20 degrees to the south of the equator angle. The -40 circle would intersect the horizon even further to the south.

          4. Umby

            Regarding my last reply a correction is in order. I have juxtaposed the numbers 42 and 48; please bare that in mind when reading my reply

  4. Patricia

    I am a Special Education teacher teaching Math and Science. This is my first time to teach science and I am learning so much. A second chance I tell my students. My enthusiasm hopefully will push these 6th graders to be passionate or at least a little more excited about our city, Albuquerque,with its many geological finds, our states diverse volcanic deposits, and the clear skies to observe the upcoming ISON. Keep me posted and send pictures as they come in, to observe the skies.

    1. astrobob

      Hi Patricia,
      Thanks for writing. It sounds like your classes are off to a great start with the enthusiasm you have for geology and the night sky. To me, it’s all about the passion. If you have that and a decent working knowledge of your topic, you’ve got what you need to fire up your students. I’m more than happy to help if you have any questions. I’ll be covering C/2012 S1 ISON closely in the coming year.

  5. Eric

    I have been searching for an estimation of the mass and diameter of this comet but have so far found no references to it except for one small bit estimating it at about 2-3 miles diameter.
    At this time is that a reliable estimation or is it still to early to tell?

    1. astrobob

      Great questions Eric. I have yet to see a published mass and like you, have heard only an estimate of 2-3 miles for a diameter. I will share those numbers should I come across them.

  6. Carl Holloway

    Im an amature astronomer just breaking in to astrophotography and the two comets of 2013 seem like an opportunity of a lifetime,especialy for my first astro photos.I plan to have a Canon 60Da in about five weeks.Any advice as to what lenses to use?Also im curious as to the chemicle makeup of the dust and gas they shed as they near the sun.Suppose their is any cyanogen in either of the two comets like the one Dr.Carl Sagan spoke of in his Cosmos series?Should I purchase some comet pills or a gas mask?…Ha,ha!

    1. astrobob

      Hi Carl,
      I’d have a wide angle (anywhere from 35 to 16mm) handy to record a nice scene and a zoom telephoto to focus in tighter on just the comet. I use a 7-200mm lens. If you can afford it, buy the fast f/2.8 versions of these lenses so you can maker shorter exposures that won’t show the comet or stars trailing. Comets are composed mostly of water ice but also contain carbon monoxide, carbon dioxide, methane and ammonia ices. Mixed in are rocks and dust that contain olivine and even organic compounds like ethanol and even amino acids. Many comet nuclei are quite dark, coated in what many scientists believe are dark, tar-like organics. Most comets near the sun develop two tails – a dust tail from the fine rock dust blown back from the nucleus by the sun and an ion tail, composed of glowing ionized carbon monoxide gas that has vaporized from the nucleus.

  7. Paola

    Hello, i have to do an oral reort about the commet ISON. One of the questions i have to answer is if the commet orbits the sun, if it does how long does it take to orbit the sun ?

  8. cheyenne

    Nice story I am a nerd and this was one thing I did not know about comets… I LOVE science alot!!! Do u thank there will be any more comets that will come out of now where? Comets are beast!!!Don’t u thank?Yes or No… Sincerly… Cheyenne

    1. astrobob

      Hi Cheyenne,
      New comets are discovered all the time, usually far away when they’re still faint. That’s what happened with ISON. Once we knew its orbit, astronomers could predict it would become (potentially) very bright. Let’s hope that happens. I love it that you love science!

  9. Jeff


    This may hae been addressed and I could have missed it, but… Has there been any estimation yet of the obital period fr this comet?

    Thank you,

  10. Which do you think will be the better views after perihelion–the evening views depicted in your chart, or the morning views before sunrise? At what dates, when ISON is within the north circumpolar stars, would the morning and evening views theoretically be about equal? Thanks for your perspective.

    1. astrobob

      For the northern hemisphere at least, I’d say the morning sky. The comet is higher up during and before dawn than after sunset. Morning and evening views will be about the same by the end of December when the comet is circumpolar in Draco.

  11. Coleen

    Dear Bob,

    When we pass through the tail of the comet twice, Nasa states we will be “double dusted” with micro meteors that will remain in the atmosphere for upwards of three years; how will that effect our climate? Will there be acid rain?

    Also, NASA just announced that a sun grazing comet caused the explosion of a neutron start in 2010, what are the chances of ISON imploding our sun?

    Also, this comet was discovered with a 15.7″ reflecting telescope, and yet we have not see ANY decent pictures coming from any of the space agencies for the “comet of the century.” Are they afraid of what we will see if we get a clear shot of what it looks like?

    Love your site!

    Thank you.

    1. astrobob

      Hi Coleen,
      Comet dust is very rarified so ISON’s effects wii be minimal. Every time we have a meteor shower – and there are half-dozen significant showers a year – we get a dusting. Desert dust, diesel exhaust, etc. are much more significant.
      Comets can’t cause things, especially neutron stars, to implode. They’re tiny and pretty insignificant. Whoever said this is mistaken.
      NASA has indeed used the Hubble and Spitzer Space Telescopes to observe and photograph the comet. More observations are planned as ISON gets closer to Earth.

    1. astrobob

      ISON is still too close to the sun and lost in daytime glare. It won’t become visible until late August low in the northeastern sky in Cancer shortly before the start of dawn. You’ll probably need at least a 10-inch telescope to see it at that time.

  12. Brian

    Hi Bob,

    I have been into astronomy for as long as I can remember, I have loads of knowledge about it but only have a 3″ meade telescope with a camera. This event excites me insanely and im preparing my equipment but Im a little confused. some say this comet will become 15 times brighter than the moon as it passes over earth dec. 26, then seem to change their mind and say its unsure. Do you by chance have any idea how bright it may be?

    And one other thing, NASA says it has 7 small asteroids accompanying it, is this also true? If so, we may be able to see them also along with the comet!

    1. astrobob

      Hi Brian,
      Thanks for writing. It’s very, very unlikely that Comet ISON will become brighter than the moon. More likely is that will briefly equal Venus in brightness but only when too close to the sun to view safely. The best time to view it will be in the few weeks of December in the morning sky. By the time it’s closest to Earth (not very close by the way at 43 million miles), it will be fading. There are no asteroids accompanying the comet despite what you might have read elsewhere.

      1. Brian

        Oh ok. I have a glass shade in case I have to do any close-to-sun observations.. so then -7 will be its best magnitude in early December?

        1. astrobob

          Current best prediction is -3 to -4. If you do attempt near-sun observations, please be sure you completely block the sun with something solid like a power pole. Should ISON only get as bright as Venus it will not be visible with the naked eye so close to the sun and will be next to impossible in binoculars because of glare. Do be careful!

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