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Encke near Perihelion - Jan 1.744, 2004

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  • terryjlovejoy
    Hi, After 3 unsuccessful days attempting to locate Comet Encke near perihelion (due to scattered cloud) I finally succeeded this morning. Unfortunately, I did
    Message 1 of 5 , Jan 1, 2004
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      Hi,

      After 3 unsuccessful days attempting to locate Comet Encke near
      perihelion (due to scattered cloud) I finally succeeded this
      morning. Unfortunately, I did not verify the comet visually since I
      was more focused on getting an image. However, a brief attempt in
      very bright twilight using 15x70 binoculars clearly revealed nothing
      brighter than magnitude 6.0. Tommorrow I will make a more serious
      attempt visually.

      Anyway, I have posted an image of Encke on my webpage at:

      http://members.ozemail.com.au/~lovejoyt/southern.htm

      Some further notes on the Encke image:

      The comet was located at 5.4 degrees elevation with the sun 12.9
      degrees below (the limiting magnitude in this image is 15 - this
      suprised me!). The ion tail is at PA 269 and is traced 20' where it
      leaves the field of view. The coma is 2.1' diameter and measured at
      total integrated mag 7.8 as compared to tycho2 Rc mags (7.5 using
      USNO 2.0 R mags). Since the comet appears quite gasy, I suspect the
      visual magnitude might be substantially higher - perhaps brighter
      than 7.0.

      And for the Afrho people, these are my Afrho values (using Tycho 2 RC
      mags and circular measurement aperture):

      98800km - 286cm
      49700km - 434cm
      24700km - 558cm

      Finally, I am somewhat dissappointed at not seeing/imaging the comet
      at perihelion as I now know it would have been quite possible. Pity
      about the cloud we had here last few days....

      Regards,
      Terry Lovejoy
    • cnj999
      ... Terry - Your observations are in very good agreement with a sighting communicated to me recently by Alan Hale. He reports spotting 2P/Encke visually at
      Message 2 of 5 , Jan 1, 2004
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        terryjlovejoy wrote:
        > Unfortunately, I did not verify the comet visually since I
        > was more focused on getting an image. However, a brief attempt in
        > very bright twilight using 15x70 binoculars clearly revealed
        > nothing brighter than magnitude 6.0.
        >
        > The coma is 2.1' diameter and measured at total integrated
        > mag 7.8 as compared to tycho2 Rc mags (7.5 using
        > USNO 2.0 R mags). Since the comet appears quite gasy, I suspect the
        > visual magnitude might be substantially higher - perhaps brighter
        > than 7.0.
        >

        Terry - Your observations are in very good agreement with a sighting
        communicated to me recently by Alan Hale. He reports spotting
        2P/Encke visually at dawn on December 27.54UT (2.34 days before
        perihelion passage) with a 41-cmL, giving the comet's total magnitude
        as about 7.0-7.5 and noting that the small, highly condensed object
        could only be followed for a very short time before being swallowed
        up in the growing light of dawn.

        He further notes that the comet could not be detected convincingly
        during previous attempts made on the mornings of December 25th and
        26th, when he was using a 20-cmL.

        Additionally, I note that your total magnitude and that of Hale's are
        in excellent agreement with brightness expectations based on Z.
        Sekanina's and my own photometric formulae derived from data gathered
        at many previous returns of this comet.

        John Bortle
      • ligustri rolando
        compliments for the result of the enterprise! Have to have a really good sky to succeed in photographing a comet at only 5 degrees on the horizon! Very
        Message 3 of 5 , Jan 1, 2004
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          compliments for the result of the enterprise! Have to have a really good sky
          to succeed in photographing a comet at only 5 degrees on the horizon! Very
          interesting the image because difference is noticed with the numerous images
          before the perielihon where the comet was very diffused, now it has a
          beautiful condensed aspect and with a hold tail of ions.

          regards
          Rolando

          > Hi,
          >
          > After 3 unsuccessful days attempting to locate Comet Encke near
          > perihelion (due to scattered cloud) I finally succeeded this
          > morning. Unfortunately, I did not verify the comet visually since I
          > was more focused on getting an image. However, a brief attempt in
          > very bright twilight using 15x70 binoculars clearly revealed nothing
          > brighter than magnitude 6.0. Tommorrow I will make a more serious
          > attempt visually.
          >
          > Anyway, I have posted an image of Encke on my webpage at:
          >
          > http://members.ozemail.com.au/~lovejoyt/southern.htm
          >
          > Some further notes on the Encke image:
        • Seiichi Yoshida
          Dear colleagues, ... I myself has been using own formulae derived from observations since its return in 1990, as posted to this list on Sept. 28. The
          Message 4 of 5 , Jan 11, 2004
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            Dear colleagues,

            John Bortle wrote:
            > Additionally, I note that your total magnitude and that of Hale's are
            > in excellent agreement with brightness expectations based on Z.
            > Sekanina's and my own photometric formulae derived from data gathered
            > at many previous returns of this comet.

            I myself has been using own formulae derived from observations since
            its return in 1990, as posted to this list on Sept. 28.

            The brightness in this return had well corresponded to the
            prediction. And the observations near the perihelion mentioned above
            also corresponded to it, too.

            I have heard that 2P/Encke has been fading since the discovery while
            it has been passing near by the Sun repeatedly every 3.3 years. But
            based on the observations since 1990, no evident long-term fading is
            found.

            Best regards,

            P.S.
            For the latest light curves of other recent comets, please see:

            http://www.aerith.net/comet/catalog/index-update.html

            --
            Seiichi Yoshida
            comet@...
            http://www.aerith.net/
          • cnj999
            ... I certainly agree with Yoshida that there has been relatively little evidence of this comet fading during the last decade or so. But 2P/Encke s secular
            Message 5 of 5 , Jan 11, 2004
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              Seiichi Yoshida wrote:
              > The brightness in this return had well corresponded to the
              > prediction. And the observations near the perihelion mentioned above
              > also corresponded to it, too.
              >
              > I have heard that 2P/Encke has been fading since the discovery while
              > it has been passing near by the Sun repeatedly every 3.3 years. But
              > based on the observations since 1990, no evident long-term fading is
              > found.
              >

              I certainly agree with Yoshida that there has been relatively little
              evidence of this comet fading during the last decade or so. But
              2P/Encke's secular decline in brightness has to be measured more in
              terms of centuries than in decades. Without question, this comet was
              much brighter in the early 1800's than it is today. It was not at all
              uncommon to see it faintly with the unaided at favorable apparitions
              during the early 19th century (1805, 1819, 1829, 1838). More
              recently, however, my nakedeye sighting in the early 1980's (when it
              was an extremely difficult nakedeye object) seems to have been the
              first such reported occurrence since the 1940's and there were very
              few such instances during the whole of the 20th century.

              There is little doubt in my mind that 2P/Encke has faded about 2 full
              magnitudes in intrinsic brightness over the course of the past two
              centuries. It is also within the realm of possibility that this comet
              only became significantly active sometime during the 18th century.
              This would tend to explain its failure to be accidentally detected if
              it had been only slightly brighter during the 16th and 17th centuries.

              Finally, Z.Sekanina points out in one of his studies on the secular
              decay of 2P/Encke that a new active region seems to have appearred on
              its surface, resulting in a slow but steady brightening of its post-T
              lightcurve, even as its pre-T intrinsic brightness is fading. He has
              suggested that in decades to common 2P/Encke might well become a far
              more prominent object for Southern Hemisphere observers than is
              currently the case.

              John Bortle
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