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Space Earth

Comet ISON Nears Date With Sun 45

Posted by timothy
from the it-is-your-destiny dept.
riverat1 writes "Now visible in the morning sky, comet ISON will swing around the Sun on November 28. ISON will pass 730,000 km above the surface of the Sun at closest approach (Mercury's perihelion distance is 46 million km). If it survives its near brush with the Sun it could provide a spectacular sky show from December into January. This NASA timeline shows that ISON will be the most observed comet ever as instruments ranging from a balloon carried telescope to the Hubble Space Telescope to the STEREO satellites will be brought into play. Lowell Observatory astronomer Matthew Knight lays out three possibilities for ISON: spontaneous disintegration before it gets to the Sun (less than 1% chance); disintegration as it rounds the Sun; or survival. If it survives, its closest approach to Earth will be on December 26 at about 1/3 of an AU."
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Comet ISON Nears Date With Sun

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  • by mcgrew (92797) * on Sunday November 17, 2013 @10:51AM (#45448219) Homepage Journal

    How visible will it be to the unaided eye? And where will it be the most visible? I was in southern Thailand when this comet [wikipedia.org] came by, and was puzzled when the newspapers said it was "disappointing". It was the brightest thing in the night sky except the moon where I was.

    • by umafuckit (2980809) on Sunday November 17, 2013 @11:02AM (#45448253)
      They probably said it was disappointing because hopes are always raised for a great, horizon to horizon, comet. It was suggested that ISON might have been one such great comet. I think it never rose above a binocular object on its way towards the sun, but things could change on the outbound journey.
    • Wikipedia says that thing was fourth magnitude when visible in the night sky: that's not very bright. But it can *seem* bright in good dark skies. Dark skies were, of course, much more common in the seventies than they are now. Light pollution eats comet tails for breakfast.

      Now, few comments (nice typo...COMETS) are really impressive in the night sky. Hale-Bopp was one exception. Most are impressive only close to the sun - this was true of Kohoutek, and will be true of ISON if it survives.

      The predictions fo

    • How visible will it be to the unaided eye?

      My guess? It won't. At least in the perihelion. Between the 0.5 degree or so of angular separation from the Sun disk and the optical effects of our atmosphere, there won't be much to see for your common Earthly gaper. Of course, the comet tail will be spectacular. But the comet itself? Nah.

    • by Zocalo (252965) on Sunday November 17, 2013 @11:52AM (#45448493) Homepage
      It's currently quite visible to the naked eye, if you can get away from any significant light pollution. You'll need to look due East just before dawn for the best views; ISON is currently passing by Spica in the constellation of Virgo [spaceweather.com]. If you've got a reasonable camera that can do manual exposures and a tripod, then you'll get a much more impressive image by using a longer exposure and a mid-telephoto focal length; a 70-200mm range is currently ideal depending on how much of the tail you want to try and capture, or go for a longer length if you just want to capture the quite spectacular coma. Open the lens to the widest aperture, manually focus to infinity (I use a bright star for this), keep the exposure down to about 20s and adjust the ISO to suit.
      • 20s is far too long at 70-200 mm, you'll turn the stars into streaks.

        Set to the highest ISO you can, set the exposure to about 2s...3s, take about 100 shots, and stack them (lots of free apps available, or photoshop, etc.)

        You want the best image, that's how you get it.

        For instance, here's a shot of a MUCH dimmer and smaller comet made just that way at 200mm; check out how you can see both the ion and dust tails:

        http://www.flickr.com/photos/48447736@N00/4695946008/ [flickr.com]

        (you can see that the 2.5s exposure there wa

    • I've heard up to 15x brighter than the moon. But it's all speculation. They do not know how much, if any of the comet will survive its encounter with the sun. It's possible it could be anywhere from barely visible or extremely spectacular. We're just going to have to wait and see. I really hope it's a dazzler though. My sons 5yrs old and I can't even put into words how fantastic an event that would be for him. It's the kind of thing that would spawn a whole generation of scientists.

      • I've heard up to 15x brighter than the moon. But it's all speculation. They do not know how much, if any of the comet will survive its encounter with the sun. It's possible it could be anywhere from barely visible or extremely spectacular. We're just going to have to wait and see. I really hope it's a dazzler though. My sons 5yrs old and I can't even put into words how fantastic an event that would be for him. It's the kind of thing that would spawn a whole generation of scientists.

        The "brighter than the moon" thing was banded around by the press, but AFAIK no reputable scientists ever expected it to get to lunar brightness.

    • See this link for some stunning imaging by amateurs: http://www.cometisonnews.com/ [cometisonnews.com]

      and this one for some serious work by 'just' an amateur: http://brucegary.net/ISON/ [brucegary.net]

      and this one which was one of the earliest to plot data (that I knew of): http://www.aerith.net/comet/catalog/2012S1/2012S1.html [aerith.net]

      Personally, from its outburst a couple of days ago, I expect it to become negative magnitude easily (the more negative, the brighter).

  • Day early, day late...either way, looks like you just follow the damn thing, find some kid in the straw, and call him the sone of a deity.

    My bet: he'll be covered in meatballs and pasta.

  • "Spontaneous"? (Score:5, Insightful)

    by fatphil (181876) on Sunday November 17, 2013 @11:06AM (#45448269) Homepage
    That word does not mean what you think it means.

    It's bombarded so aggressively, it's having its surface ripped off it to create that enormous tail, and it's suffering from ever greater gravitational tidal forces - that's about as far as you can get from happening without apparent external infuence.
    • by Travis Repine (2861521) on Sunday November 17, 2013 @11:20AM (#45448341)
      If I didn't know any better, I would say that you have feelings for this Comet.
    • "Spontaneous disintegration" is EXACTLY what "Spontaneous disintegration" means. Look up Comet LINEAR, for example. It disintegrated in August 2006 for no apparent reason, since it was not passing near the Sun or a planet when it broke apart.
      • by fatphil (181876)
        Your date or your name seem fucked up - are you referring to the comet about which NASA said:
        "In hindsight Comet LINEAR began falling apart in June when the comet unexpectedly brightened, indicating an outburst of dust. Powerful gas jets nudged the comet along a chaotic path, another indication of a very volatile activity."
        At that point, note that the comet had a very visible tail - it was being pounded constantly by the solar wind.

        If you think "unexpected" and "spontaneous" mean the same thing, please inve
    • by riverat1 (1048260)

      Since this is ISON's first encounter with the Sun it's unclear how well consolidated the comet is. As I said less than 1% of comets fall apart like this before they get to the Sun but you don't know if it will until it happens (or doesn't).

    • It's bombarded so aggressively, it's having its surface ripped off it to create that enormous tail, and it's suffering from ever greater gravitational tidal forces - that's about as far as you can get from happening without apparent external infuence.

      This is what bugs me about the prediction of closest Earth approach "if it survives".

      Now, I'm not sure about this... but it is necessarily on a hyperbolic trajectory. Does the trajectory stay approximately the same if it breaks up and therefore changes mass? I.e., if it's a relatively passive breakup (by no means a given), would all the pieces continue in the same trajectory? Or is it altered?

      • Re:"Spontaneous"? (Score:4, Informative)

        by fatphil (181876) on Sunday November 17, 2013 @03:23PM (#45449651) Homepage
        The centre of mass of the fragments will continue in the same path initially. However, the smaller the fragment, the more the solar wind will affect it. Some groups of comets that appear at about to have a very similar path have been conjectured to be just components of much larger comets that have fragmented (e.g. the Kreutz group).
        • The centre of mass of the fragments will continue in the same path initially.

          Good answer. I should have thought of that.

  • by Anonymous Coward
    Somebody queue the "three wise men", of Biblical fame.
  • Comet ISDN? (Score:2, Funny)

    by Anonymous Coward

    Old news. Tell me when Comet ADSL is heading our way.

  • What distinguishes comets is not only their insanely eccentric orbits but also their predominantly icy makeup, right? Will it still have any ice or other volatiles after such a close pass with the sun? If all that volatile mass burns off, won't that significantly alter its orbit thereafter?

    • That was my question too. Or close to it. Will the trajectory change much (or at all) if it breaks up or loses mass during its swing around the sun?

      I admit that I don't know enough about the mechanics to know the answer off-hand.
  • with all the *son technologies, it is hard to keep track :p

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