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Re: [comets-ml] ISON on the Web

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  • jbortle@aol.com
    While I must sadly agree with Dave about the current hype and the even worse hype likely yet to come involving Comet ISON, I think that the question of at
    Message 1 of 24 , Dec 12, 2012
      While I must sadly agree with Dave about the current hype and the even
      worse hype likely yet to come involving Comet ISON, I think that the question
      of at least somewhat reliably predicting the future brightness of most
      comets is less far less mystical guesswork than many seem to assume. I have
      never ascribed to David Levy's often quoted assertion that, "Comets are like
      cats, they have tail and do precisely what they want." In my opinion to a
      significant degree they are predictable. Let me elaborate.

      If one examines the historical record it can be reasonably demonstrated,
      especially in recent decades where comets are being discovered at
      increasingly larger heliocentric distances, that dynamically "new" comets typically
      have a very poor performance record. Conversely, those that can be clearly
      identified as returning "old" objects generally do follow predictions quite
      well providing there are no disruption events. It is to be noted that "new"
      comets quite often will exhibit "n" values noticeably, sometimes even
      strikingly, higher than 4 in their early photometric behavior, while older ones
      do not. Quite honestly, the only "new" comet to very clearly violate this
      trend in my 50+ years of observing experience was McNaught's Great Comet.

      Comet Seki-Lines was perhaps the one other highly peculiar object in my
      experience. Not only did it fail to become a daylight object even though it
      brightened very steadily to within just a couple of days of perihelion and
      reappeared as a brilliant object only shortly after T (according to a study
      I read, the nucleus seemingly turned off at perihelion!), but the tail it
      developed post-T was rather uncharacteristic of a Sunskirting comet as
      well. There was certainly something odd about it as a comet.

      Likewise, the perihelion survival cutoff parameter I defined some 20 years
      ago has served very well in indicating which in-bound new comets were
      likely to disrupt, or just fade away, with their approach to the Sun. Mailing
      List readers will recall that, amid all the initial hype, virtually from the
      outset I was predicting that Comet Elenin would likely fail to
      survive...and didn't. Among questionable perihelion survival comets only McNaught's
      comet, one near the margin line of survival and the more recent sungrazing
      Comet Lovejoy, were dramatic exceptions to the longstanding rule. And these
      two objects I consider to each have been unquestionably extraordinary, if not
      absolutely unique, among comets in their overall behavior.

      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







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



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

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      [Non-text portions of this message have been removed]
    • Pheromons
      I agree with you... Only, some interesting comets have fooled us lot - a lot! Besides that, I concur with you 100%... Yours sincerely, Shri Krishna Yadav,
      Message 2 of 24 , Dec 12, 2012
        I agree with you...

        Only, some interesting comets have fooled us 'lot' - a lot!

        Besides that, I concur with you 100%...

        Yours sincerely,

        Shri Krishna Yadav,
        Indian Space Research Pvt. Ltd,
        New Delhi.
        -Sent via iPhone4S

        On 12-Dec-2012, at 8:05 PM, jbortle@... wrote:

        [Fullquote deleted by moderator]
      • David Seargent
        Hi John and all, I have long suspected that McNaught s great comet was an imposter! I mean, a dynamically old comet that had been flung back out into the Oort
        Message 3 of 24 , Dec 12, 2012
          Hi John and all,
          I have long suspected that McNaught's great comet was an imposter! I mean, a dynamically old comet that had been flung back out into the Oort Cloud at a previous return. We recall that the future orbit of Comet West places its aphelion back in the Oort Cloud, so that when it returns about a million years hence, it will arrive on an orbit that it indistinguishable from that of a new comet. McNaught simply did not act like a new comet, as you point out, but ISON appears to be acting this way in that it must have a good store of surface volatiles to be active at its present distance. I doubt that it would be capable of retaining this supply if it had previously passed just 0.01 AU from the Sun.
          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





          If one examines the historical record it can be reasonably demonstrated,
          especially in recent decades where comets are being discovered at
          increasingly larger heliocentric distances, that dynamically "new" comets typically
          have a very poor performance record. Conversely, those that can be clearly
          identified as returning "old" objects generally do follow predictions quite
          well providing there are no disruption events. It is to be noted that "new"
          comets quite often will exhibit "n" values noticeably, sometimes even
          strikingly, higher than 4 in their early photometric behavior, while older ones
          do not. Quite honestly, the only "new" comet to very clearly violate this
          trend in my 50+ years of observing experience was McNaught's Great Comet.

          J.Bortle






          Comet Observations List: http://groups.yahoo.com/group/CometObs/
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          .





          [Non-text portions of this message have been removed]
        • Jakub Cerny
          Hello David, I think that scenario that you described is quite real and it must happen sometimes. Therefore apperance of peculiar comets like McNaught is very
          Message 4 of 24 , Dec 12, 2012
            Hello David,

            I think that scenario that you described is quite real and it must
            happen sometimes. Therefore apperance of peculiar comets like McNaught
            is very probable.

            Jakub

            On 12/13/2012 12:47 AM, David Seargent wrote:
            > Hi John and all,
            > I have long suspected that McNaught's great comet was an imposter! I mean, a dynamically old comet that had been flung back out into the Oort Cloud at a previous return. We recall that the future orbit of Comet West places its aphelion back in the Oort Cloud, so that when it returns about a million years hence, it will arrive on an orbit that it indistinguishable from that of a new comet. McNaught simply did not act like a new comet, as you point out, but ISON appears to be acting this way in that it must have a good store of surface volatiles to be active at its present distance. I doubt that it would be capable of retaining this supply if it had previously passed just 0.01 AU from the Sun.
            > 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
            >
            >
            >
            >
            >
            > If one examines the historical record it can be reasonably demonstrated,
            > especially in recent decades where comets are being discovered at
            > increasingly larger heliocentric distances, that dynamically "new" comets typically
            > have a very poor performance record. Conversely, those that can be clearly
            > identified as returning "old" objects generally do follow predictions quite
            > well providing there are no disruption events. It is to be noted that "new"
            > comets quite often will exhibit "n" values noticeably, sometimes even
            > strikingly, higher than 4 in their early photometric behavior, while older ones
            > do not. Quite honestly, the only "new" comet to very clearly violate this
            > trend in my 50+ years of observing experience was McNaught's Great Comet.
            >
            > J.Bortle
            >
            >
            >
            >
            >
            >
            > Comet Observations List: http://groups.yahoo.com/group/CometObs/
            > Comet Images List: http://groups.yahoo.com/group/Comet-Images/
            >
            > NOTICE: Material quoted or re-posted from the Comets Mailing List should be indicated by:
            >
            > Comets Mailing List [date]
            > http://www.yahoogroups.com/group/comets-ml
            >
            >
            > Switch to: Text-Only, Daily Digest • Unsubscribe • Terms of Use • Send us Feedback
            >
            >
            > .
            >
            >
            >
            >
            >
            > [Non-text portions of this message have been removed]
            >
            >
            >
            > ------------------------------------
            >
            > Comet Observations List: http://groups.yahoo.com/group/CometObs/
            > Comet Images List: http://groups.yahoo.com/group/Comet-Images/
            >
            > NOTICE: Material quoted or re-posted from the Comets Mailing List should be indicated by:
            >
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            >
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            >
            >
          • David Seargent
            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,
            Message 5 of 24 , Dec 12, 2012
              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

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

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

              Comet Observations List: http://groups.yahoo.com/group/CometObs/
              Comet Images List: http://groups.yahoo.com/group/Comet-Images/

              NOTICE: Material quoted or re-posted from the Comets Mailing List should
              be indicated by:

              Comets Mailing List [date]
              http://www.yahoogroups.com/group/comets-ml
              Yahoo! Groups Links

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






              [Non-text portions of this message have been removed]
            • 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 6 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

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

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

                Comet Observations List: http://groups.yahoo.com/group/CometObs/
                Comet Images List: http://groups.yahoo.com/group/Comet-Images/

                NOTICE: Material quoted or re-posted from the Comets Mailing List should
                be indicated by:

                Comets Mailing List [date]
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                Yahoo! Groups Links

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






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



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

                Comet Observations List: http://groups.yahoo.com/group/CometObs/
                Comet Images List: http://groups.yahoo.com/group/Comet-Images/

                NOTICE: Material quoted or re-posted from the Comets Mailing List should
                be indicated by:

                Comets Mailing List [date]
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                Yahoo! Groups Links






                [Non-text portions of this message have been removed]
              • 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 7 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 8 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 9 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 10 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 11 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 12 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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