Loading ...
Sorry, an error occurred while loading the content.
 

C/ISON's Current Status and Potential Future

Expand Messages
  • cnj999
    In looking at the most recent photometric data, it would appear that C/ISON s absolute magnitude (assuming a change in heliocentric brightness in step with the
    Message 1 of 3 , May 30, 2013
      In looking at the most recent photometric data, it would appear that
      C/ISON's absolute magnitude (assuming a change in heliocentric brightness in
      step with the typical 8.3 log r) is close to magnitude 7.5 currently.
      Under normal circumstances this would make ISON similar to many modestly
      bright (i.e. "average") comets seen in the past. However, with this comet's
      exceedingly small perihelion distance the ultimate situation is less clear.

      Comet Ikeya-Seki of 1965, with an absolute magnitude of 6.5 , appears to
      represent the faintest major sungrazer/sun-skirting comet to have survived
      perihelion essentially intact. The non-surviving sungrazing comets of 1880
      and 1887 were "thought" to have absolute magnitudes of around 7.0-7.5 ,
      although this might be open to question. Then there is Lovejoy's recent comet
      that violated all the rules and was intrinsically quite faint, ultimately
      classified as a member of the non-survival group. So...where will C/ISON fall?
      This is really difficult to predict at the moment. However, I would like
      to offer the following tentative prognostication.

      Comet ISON will develop more slowly in the autumn morning sky than had been
      initially hoped for. It will not actually attain naked eye brightness
      until just a week, or two, before perihelion passage. By then it will already
      be descending into the morning twilight. On perihelion day the comet may
      attain -6 very briefly (hours) and be visually detected near the Sun using
      great caution, then immediately begin to fade rapidly.

      As the comet retreats from the Sun its head will be brighter than
      magnitude +2 or +3 for just a few days, but it will be beginning to unfurl an
      extraordinary long straight tail of considerable surface brightness, at least
      initially. This tail could reach 30 or perhaps even 45 degrees in length a
      week post-T, but its visibility with the naked eye will rapidly wane. The
      tail's impressive visual show will last perhaps no more than a week to ten
      days in total. Thereafter, like C/Lovejoy, ISON's photographic tail will
      continue to lengthen and fade for some time. Concurrent to this the comet's head
      will likely dissipate more-or-less in the same manner as did Lovejoy's,
      with Comet ISON becoming a "Headless Wonder" by mid December, or very soon
      thereafter.

      I would anticipate that any further critical predictions of this comet's
      future behavior will have to wait until at least early September.

      J.Bortle







      [Non-text portions of this message have been removed]
    • David Seargent
      Kreutz comets might behave more like short-period objects in certain respects. Very few have been discovered prior to perihelion which probably indicates that
      Message 2 of 3 , May 30, 2013
        Kreutz comets might behave more like short-period objects in certain respects. Very few have been discovered prior to perihelion which probably indicates that the initial increase in brightness is very steep. A good case in point is C/White-Ortiz-Bolelli in 1970 which should have been an easy discovery in the weeks before perihelion. The 1945 object (which was discovered well before perihelion but then faded out) was probably in outburst at discovery and may have been a very small and fragile object that was breaking apart when found. In general, the "typical" Kreutz behaviour may be more like Lovejoy than Ikeya-Seki. This probably does not apply directly to ISON which appears to be a "first-time" comet, but John's predictions will likely turn out to be close to reality I think. The present brightness formula makes naked-eye observing prior to perihelion seem rather doubtful, especially with an inconvenient mid-month full moon and the comet's position low in the morning twilight, so it is the post-T performance that will probably make or break this comet's reputation!

        Regards,

        David





        To: comets-ml@yahoogroups.com
        From: jbortle@...
        Date: Thu, 30 May 2013 10:23:51 -0400
        Subject: [comets-ml] C/ISON's Current Status and Potential Future







        In looking at the most recent photometric data, it would appear that
        C/ISON's absolute magnitude (assuming a change in heliocentric brightness in
        step with the typical 8.3 log r) is close to magnitude 7.5 currently.
        Under normal circumstances this would make ISON similar to many modestly
        bright (i.e. "average") comets seen in the past. However, with this comet's
        exceedingly small perihelion distance the ultimate situation is less clear.

        Comet Ikeya-Seki of 1965, with an absolute magnitude of 6.5 , appears to
        represent the faintest major sungrazer/sun-skirting comet to have survived
        perihelion essentially intact. The non-surviving sungrazing comets of 1880
        and 1887 were "thought" to have absolute magnitudes of around 7.0-7.5 ,
        although this might be open to question. Then there is Lovejoy's recent comet
        that violated all the rules and was intrinsically quite faint, ultimately
        classified as a member of the non-survival group. So...where will C/ISON fall?
        This is really difficult to predict at the moment. However, I would like
        to offer the following tentative prognostication.

        Comet ISON will develop more slowly in the autumn morning sky than had been
        initially hoped for. It will not actually attain naked eye brightness
        until just a week, or two, before perihelion passage. By then it will already
        be descending into the morning twilight. On perihelion day the comet may
        attain -6 very briefly (hours) and be visually detected near the Sun using
        great caution, then immediately begin to fade rapidly.

        As the comet retreats from the Sun its head will be brighter than
        magnitude +2 or +3 for just a few days, but it will be beginning to unfurl an
        extraordinary long straight tail of considerable surface brightness, at least
        initially. This tail could reach 30 or perhaps even 45 degrees in length a
        week post-T, but its visibility with the naked eye will rapidly wane. The
        tail's impressive visual show will last perhaps no more than a week to ten
        days in total. Thereafter, like C/Lovejoy, ISON's photographic tail will
        continue to lengthen and fade for some time. Concurrent to this the comet's head
        will likely dissipate more-or-less in the same manner as did Lovejoy's,
        with Comet ISON becoming a "Headless Wonder" by mid December, or very soon
        thereafter.

        I would anticipate that any further critical predictions of this comet's
        future behavior will have to wait until at least early September.

        J.Bortle







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







        [Non-text portions of this message have been removed]
      • biver_nicolas
        I am perfectly inline with what John Bortle just said... and getting a bit skeptical by some big fuss about international (professional) observing campaigns
        Message 3 of 3 , Jun 3, 2013
          I am perfectly inline with what John Bortle just said... and getting a bit skeptical by some big fuss about international (professional) observing campaigns that should probably be a little more cautious about the performance of the comet.
          If it behaves as the dusty dynamically new Oort cloud comet C/2011 L4 we just saw (and disintegrate shortly after perihelion), then it may just perform as a small yearly comet, only before perihelion when beyond 30 deg. from the Sun reaching an outagssing rate on the order of 5 tons/s at 0.5 AU from the sun - similar to what comet Lemmon is still outgassing now at 1.4 AU from the Sun.
          I have updated my mh(rh) plot at :
          http://www.lesia.obspm.fr/perso/nicolas-biver/cometsmagpreperi-2011l4-2012s1.jpg

          I did try to see it in good observing conditions on the 10th of May with my 16" dobsonian, but could see anything convingly brighter than m1=15.0 (nearby stars down to 16.0) - while C/2011 L4 in early june 2012 (when further away from the Sun but closer to ther Earth) although the illumination difference was only 0.2 mags, was quite easy in a 8" scope!

          Lets hope for better, but until it reaches 0.3 AU, we should look at it as a new Oort cloud comet like PanSTARRS, and wait until October when it crosses the ~1.5 AU limit to see its real activity.

          Nicolas
        Your message has been successfully submitted and would be delivered to recipients shortly.