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Re: [comets-ml] ISON on the Web

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  • jbortle@aol.com
    Dave, I would think that any fragmentation even resulting in the separation of Comet ISON from the Great Comet of 1680 would likely have occurred quite near
    Message 1 of 24 , Dec 13, 2012
      Dave, I would think that any fragmentation even resulting in the separation
      of Comet ISON from the Great Comet of 1680 would likely have occurred
      quite near the time of perihelion passage as the perihelion points of both
      orbits almost coincide (perhaps they even precisely do, considering the
      possible uncertainties in the 1680 object's orbital elements). Similarly, the
      velocities involved in a separation at say less than 0.1 a.u. of the Sun would
      be much higher than might be anticipated if it were to have occurred a
      some huge heliocentric distance. Likewise, I don't believe that a distance
      disruption event would result in their aphelion diverging so much. Given the
      magnitude of the deviations in the two orbits' aphelion directions it
      therefore seems to me much more difficult to accept a breakup far from the Sun at
      low velocity of a few meters per second.

      I would also comment that IF (still a big "if" here) the Great Comet of
      1680 and ISON are truly directly related, then the separation of more than
      300 years in the dates of their perihelia implies to me that the revolution
      period of the 1680 object is likely to be much longer than assumed and has
      an orbital eccentricity considerably greater than currently cataloged, at
      least if the break-up occurred only one revolution ago. Recall that the
      individual nucleii of the Great September Comet of 1882 had periods separated by
      only about one hundred years each, yet their overall orbital periods were
      in the order of 1,000 years.

      In addressing relative magnitudes of the two bodies, the intrinsic
      brightness of the two may be even less clear. Unquestionably the 1680 comet was
      spectacular, but like Comet Hykutake, the 1680 comet was observed under
      extraordinarily favorable circumstances influencing its perception by observers
      Based on the crude brightness observations of the period it has been
      generally assumed that the Great Comet of 1680 had an H10 value of about 5.0 .
      Currently we are "assuming" ISON to be roughly H10 = 6.0 at its current
      heliocentric distance. To my mind, considering what I will point out below, it
      is possible that there may really be very little, if any, difference between
      the intrinsic brightness of the two.

      The as yet little appreciated observational factor involved with both of
      these comets is the nature of tail development commonly exhibited in the case
      of Sungrazing/Sunskirting comets: their tails can often be utterly unique
      and fully orders of magnitude in surface brightness greater than those of
      their comparably H10 brethren, especially when observed under favorable
      view circumstances. You and I can fully appreciate this factor in having seen
      Comet Ikeya-Seki at its best back in 1965 (and others perhaps to a lesser
      degree with recent Comet Lovejoy), but the great bulk of observers today
      cannot begin to appreciate the significance of this in terms of ISON's coming
      apparition.

      If Comet ISON can survive perihelion passage (and major
      Sungrazing/Sunskirting comets seems all to be quite able to do so, implying that they must
      all be dynamically "old" objects), then we are almost surely in for a
      striking display in the morning sky as Comet ISON recedes from the Sun next
      December. It's immense tail, partly the result of our extremely favorable viewing
      circumstances in this case and just as with the Great Comet of 1680 -
      could well result in a tail of amazing length and surface brightness, even if
      tipped by a only tiny, relatively insignificant head.

      J.Bortle



      .



      In a message dated 12/13/2012 12:37:26 A.M. Eastern Standard Time,
      seargent@... writes:


      One further thought about this. I just wonder if it is possible that the
      1680 was dynamically new and that ISON split away from it at Oort-Cloud
      distances or, in any case, at very large distances from the Sun. The 1680 comet
      was certainly spectacular, but we don't know its brightness at ISON's
      present distance. Maybe it was a lot brighter then (in terms of absolute
      magnitude) than it was during its observed period!
      Cheers,
      David




      To: comets-ml@yahoogroups.com
      From: jbortle@...
      Date: Wed, 12 Dec 2012 09:35:47 -0500
      Subject: Re: [comets-ml] ISON on the Web





      Addressing pending comet ISON, I still hold the opinion that it is in some
      fashion related to the Great Comet of 1680 for several good reasons.
      Orbital catalogs indicate the 1680 object to have been following an
      exceedingly
      elongated ellipse, the crude observations of the day fitting an orbit
      with"e" close to 0.99999 . That it could be even a bit more eccentric, but
      still
      not quite parabolic, is certainly not an unreasonable assertion.

      Precise eccentricity is not easily determined at large heliocentric
      distances for comets with vanishing small values of "q", so perhaps Comet
      ISON
      may yet be found to be periodic. If indeed perhaps with a period of some
      tens
      of thousands of years, then Comet ISON could conceivably be a major
      fragment which separated from the 1680 comet one or two returns ago,
      making it
      also dynamically "old" and potentially a good performer near perihelion.

      While I cannot ascribe to some of the outlandish magnitude predictions
      I've
      seen on Internet forums, I do see ISON attaining a very significant
      negative magnitude when at perihelion. Perhaps even more important, and
      regardless of whether its nucleus survives its brush with the Sun fully
      intact, or
      disrupts hours or days thereafter, I anticipate a post perihelion tail
      display in latter December next that will be virtually second to none:
      imagine
      Comet Lovejoy on steroids.

      J.Bortle





      In a message dated 12/12/2012 12:29:49 A.M. Eastern Standard Time,
      seargent@... writes:

      The comet MIGHT reach negative magnitudes, but that does not mean
      outshining the Moon and casting shadows! In many respects, this comet
      seems similar
      to Seki-Lines in 1962 - each appears dynamically new, of similar intrinsic
      brightness and each a deep sunskirter. S-L became an impressive object
      with a strong tail, although it did not become visible in daylight as had
      been
      predicted. If ISON behaves similarly, it might not become a super-comet
      but it will still be a nice object. The only thing that could then spoil
      it
      is if people were made to expect something far more spectacular because of
      irresponsible hype!
      Cheers,
      David

      To: comets-ml@yahoogroups.com
      From: dfischer@...-bonn.de
      Date: Wed, 12 Dec 2012 00:57:03 +0100
      Subject: Re: [comets-ml] ISON on the Web

      > Anyway, here endeth the rant!

      And so spoke Ernesto Guido, the late Giovanni Sostero and Nick Howes in
      http://remanzacco.blogspot.it/2012/09/new-comet-c2012-s1-ison.html
      immediately after the discovery: "According to its orbit, this comet might
      become a naked-eye object in the period November 2013 - January 2014. And
      it might reach a negative magnitude at the end of November 2013." As far
      as I know nothing has changed in this respect - so what is there *not* to
      get suitably excited about ...?

      In a more urgent matter, the heated discussion here from October on where
      C/2011 L4 (PANSTARRS) may be headed brightness-wise has long died down,
      without any insights gained. The 'critical' distance from the Sun, 1.5 AU,
      where according to some pessimists the lightcurve will bend down, will
      only be reached in early January, so we only have the past lightcurve -
      fuzzily pointing to a -1 mag. peak in
      http://www.aerith.net/comet/catalog/2011L4/2011L4.html - and comparisions
      with other comets to work with.

      Any new insights/opinions would be highly welcome, in the context of
      certain publicistic preparations that are due this month ...

      Daniel

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      ------------------------------------

      Comet Observations List: http://groups.yahoo.com/group/CometObs/
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      NOTICE: Material quoted or re-posted from the Comets Mailing List should
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    • tonyjhoffman
      As a journalist who occasionally gets to write articles about astronomy (although usually I have to do it on my own time), I am appalled (though not surprised)
      Message 2 of 24 , Dec 17, 2012
        As a journalist who occasionally gets to write articles about astronomy (although usually I have to do it on my own time), I am appalled (though not surprised) by the amount of disinformation--sometimes honest mistakes but often exaggeration and hyperbole, if I may apply a cometary term to a terrestrial problem--in articles on astronomical topics. I expect nonsense in certain quarters, but astronomy publication that should have known better was touting Comet ISON as potentially a "once-in-a-civilization's-lifetime" event, and at least one other was clearly overhyping the comet's prospects. Kohoutek was the first comet I ever observed, so my experience has taught me to be cautious when it comes to claims about comets, and I've tried to present a balanced account in the two stories I've written about Comet ISON. Of course even if a sungrazer or sunskirter approaches the brightness of the Full Moon, it's not an apt comparison because you're seeing it in the daylight sky when right near the Sun.

        David, I enjoyed your e-book on sungrazing comets. One of the points I found most interesting is your idea that there may be a de facto cap on the apparent magnitude of sungrazers, or indeed any comet, of between -11 and -13 or thereabouts, that even with forward scattering they generally don't approach their brightness would indicate based on their absolute magnitudes, and that sunskirters even more than sungrazers tend to lag.

        On a personal note, I was thrilled to see that you included the photo of Ikeya-Seki in twilight that graced article on said comet inthe February 1966 (if I recall right) issue of National Geographic. In the early 1970s I came across that issue at a yard sale, with its cover headline "Giant Comet Grazes the Sun", and that issue ignited my interest in comets, and especially in sungrazers. I still have it here somewhere.

        Tony


        --- In comets-ml@yahoogroups.com, David Seargent wrote:

        Hi all,

        Have you read the tripe about C/ISON that is being published on the Web at present? I am old enough to recall C/Kohoutek in 1973 and much of this sounds all-too-familiar. Did you know that;
        ISON is as large as Hale-Bopp,
        will be at least as bright as the full Moon and cast shadows at night
        might be a return of the Comet of 1680
        is a sign of the end of the world and the Second Coming of Christ?

        With respect to the latter, my Bible says that not even Jesus knew when this would happen, so I don't know where the "prophet" saying this gets his info!
        Regarding the more "scientific"(?) statements, ISON appears to be a new comet (unlike H-B) so its present activity far from the Sun is likely due to surface volatiles rather than large size. Even so, it is intrinsically MUCH fainter than H-B with most CCD estimates indicating an absolute magnitude near 6. It does not appear to be very large; probably average size.
        These sort of statements either frighten people or build up unrealistic hopes, but they will probably get even worse as the time approaches! We may need to come out with some sane statements to counter the sensation-mongers and the cranks in the year ahead. Anyway, here endeth the rant!
        Cheers,
        David

        [Non-text portions of this message have been removed]
      • stuartatkinson2013
        Hi all, Amateur astronomer/writer/Outreach educator just joined the Group and really looking forward to following PANSTARRS and ISON with all of you! Going to
        Message 3 of 24 , Dec 31, 2012
          Hi all,

          Amateur astronomer/writer/Outreach educator just joined the Group and really looking forward to following PANSTARRS and ISON with all of you! Going to be challenging for me, living here in the Lake District in the UK (we have lakes because of all the rain...makes sense!) but can't wait for March and then November. I agree that web coverage of these comets is going to be dreadful in someplaces, and will lead to major disappointment for some people. I've created a blog (link below) which will,hopefully, be useful for people wanting to enjoy these comets, but I go to great pains to stress that we just don't know how bright they will be, so everyone needs to be both patient and realistic. Crossing my fingers and hoping for the best tho!

          My blog: http://waitingforison.wordpress.com/
        • dfischer@astro.uni-bonn.de
          ... Which in itself leads to a misunderstanding: as we have learned from the McNaught 2007 and Lovejoy experiences the (coma total) brightness is far less
          Message 4 of 24 , Dec 31, 2012
            > I go to great pains
            > to stress that we just don't know how bright they will be

            Which in itself leads to a misunderstanding: as we have learned from the
            McNaught 2007 and Lovejoy experiences the (coma total) brightness is far
            less important than the dust tail size and surface brightness that make or
            break a Great Comet for the public at large - and two aren't directly
            correlated, with the tail show lagging well behind coma development.
            Wonder if and when reliable predictions for PANSTARRS' and ISON's dust
            tails might become available.

            Now you could say: "just wait and see;" if the tail of either comet
            McNaught-ifies, the world will get it early enough. But for well-organized
            astronomy outreach such advance knowledge would be an advantage. And those
            challenged by viewing geometry and/or weather would appreciate early
            advice on whether to travel. A daring German astronomy tour operator has
            already chartered a plane for a PANSTARRS observing flight out of Cologne
            on 16 March, you know ...

            Daniel
          • Harry Geist (OOL)
            You are correct, which is why my FB comment included the phrases: if predictions hold, we could all witness. , potentially , perhaps brighter than the full
            Message 5 of 24 , Dec 31, 2012
              You are correct, which is why my FB comment included the phrases: "if
              predictions hold, we could all witness.", "potentially", "perhaps brighter
              than the full moon", "it's not a sure thing", and "hope for a spectacular
              nighttime show." I thought I couched my posting in enough language to say
              "it's not definite." Maybe I shouldn't have written anything, but I thought
              it was worth mentioning.





              Harry Geist

              hgeist@...





              From: comets-ml@yahoogroups.com [mailto:comets-ml@yahoogroups.com] On Behalf
              Of dfischer@...-bonn.de
              Sent: Monday, December 31, 2012 9:41 AM
              To: comets-ml@yahoogroups.com
              Subject: Re: [comets-ml] Re: ISON on the Web





              > I go to great pains
              > to stress that we just don't know how bright they will be

              Which in itself leads to a misunderstanding: as we have learned from the
              McNaught 2007 and Lovejoy experiences the (coma total) brightness is far
              less important than the dust tail size and surface brightness that make or
              break a Great Comet for the public at large - and two aren't directly
              correlated, with the tail show lagging well behind coma development.
              Wonder if and when reliable predictions for PANSTARRS' and ISON's dust
              tails might become available.

              Now you could say: "just wait and see;" if the tail of either comet
              McNaught-ifies, the world will get it early enough. But for well-organized
              astronomy outreach such advance knowledge would be an advantage. And those
              challenged by viewing geometry and/or weather would appreciate early
              advice on whether to travel. A daring German astronomy tour operator has
              already chartered a plane for a PANSTARRS observing flight out of Cologne
              on 16 March, you know ...

              Daniel





              [Non-text portions of this message have been removed]
            • Owen Brazell
              I would think that given the weather here in the uk it might be good for someone to arrange trips from here in uk as well :-) Owen Sent from my iPad ...
              Message 6 of 24 , Dec 31, 2012
                I would think that given the weather here in the uk it might be good for someone to arrange trips from here in uk as well :-)

                Owen



                Sent from my iPad

                On 31 Dec 2012, at 14:41, dfischer@...-bonn.de wrote:

                > > I go to great pains
                > > to stress that we just don't know how bright they will be
                >
                > Which in itself leads to a misunderstanding: as we have learned from the
                > McNaught 2007 and Lovejoy experiences the (coma total) brightness is far
                > less important than the dust tail size and surface brightness that make or
                > break a Great Comet for the public at large - and two aren't directly
                > correlated, with the tail show lagging well behind coma development.
                > Wonder if and when reliable predictions for PANSTARRS' and ISON's dust
                > tails might become available.
                >
                > Now you could say: "just wait and see;" if the tail of either comet
                > McNaught-ifies, the world will get it early enough. But for well-organized
                > astronomy outreach such advance knowledge would be an advantage. And those
                > challenged by viewing geometry and/or weather would appreciate early
                > advice on whether to travel. A daring German astronomy tour operator has
                > already chartered a plane for a PANSTARRS observing flight out of Cologne
                > on 16 March, you know ...
                >
                > Daniel
                >
                >


                [Non-text portions of this message have been removed]
              • jbortle@aol.com
                In a message dated 12/31/2012 9:44:00 A.M. Eastern Standard Time, ... Which in itself leads to a misunderstanding: as we have learned from the McNaught 2007
                Message 7 of 24 , Dec 31, 2012
                  In a message dated 12/31/2012 9:44:00 A.M. Eastern Standard Time,
                  dfischer@...-bonn.de writes:

                  > I go to great pains
                  > to stress that we just don't know how bright they will be

                  Which in itself leads to a misunderstanding: as we have learned from the
                  McNaught 2007 and Lovejoy experiences the (coma total) brightness is far
                  less important than the dust tail size and surface brightness that make or
                  break a Great Comet for the public at large - and two aren't directly
                  correlated, with the tail show lagging well behind coma development.
                  Wonder if and when reliable predictions for PANSTARRS' and ISON's dust
                  tails might become available.

                  Daniel

                  The question of the degree of dust tail development in potential Great
                  Comets is hardly as much of a total unknown as implied here and most certainly
                  a comet's intrinsic magnitude is a basic, if not THE crucial factor
                  governing it.

                  One needs to be exceedingly cautious about employing only a couple of
                  decidedly unusual, if not downright unique comets, in support of any sweeping
                  statement concerning how Great Comets do or do not behave. In fact, dust
                  tail development and the visual prominence of comets that closely approach the
                  Sun are intimately related to intrinsic brightness, there being only a
                  handful of true exceptions to this over the course many decades, if not
                  hundreds of years.

                  Those comets showing a high, stabile, intrinsic brightness and having
                  perihelia significantly less than 1 au will nearly always display an impressive
                  dust tail given favorable viewing geometry, a factor that in itself can
                  play an most interesting role. In general, high intrinsic brightness in a
                  comet signals the probability of a high dust production rate. Conversely,
                  comets of low intrinsic brightness (fainter than m10 = 7.5) typically are much
                  more gas dominated objects and only under highly unusual circumstances can
                  they generate a significant and bright dust tail.

                  Prognosticating the size, brightness, and general appearance of a major
                  comet's dust tail is not necessarily just a shot in the dark. It is the
                  ascertaining of an accurate intrinsic magnitude for the comet once it has come
                  within about 1.5 au of the Sun that will indicate to the observer what the
                  object's future development will likely be. The major difficulty with both
                  brightness and physical development predictions today is that most comets are
                  now discovered at enormous solar distances and conditions prevailing there
                  governing their activity do not directly translate to what will be the
                  case much closer in to the Sun. Any early parameters/predictions become even
                  more dubious with regard to Oort Cloud comets.

                  All that said, when PANSTARRS, or ISON, are a month or so short of their
                  perihelia, be assured that it will be reasonably possible to predict their
                  dust tail's prominence and appearance to the unaided eye once they have
                  rounded the Sun.

                  J.Bortle


                  [Non-text portions of this message have been removed]
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