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

Re: [comets-ml] C/2010 X1 remnant, and other things.

Expand Messages
  • Juan José González Suárez
    Alan, Richard, Jakub, Nicolas, Dave, Mike, and friends, Some days ago, I started a mail to this list with some lines of California Dreamin (1965). Let me
    Message 1 of 24 , Oct 28, 2011
      Alan, Richard, Jakub, Nicolas, Dave, Mike, and friends,

      Some days ago, I started a mail to this list with some lines of
      "California Dreamin" (1965).
      Let me begin today with other song of the same year, another one of my
      most favorite songs, ( for obvious reasons ... ), "Sound of Silence":
      "Hello darkness, my old friend ... I've come to talk with you again ...
      ... and the vision that was planted in my brain ... still remains ..."
      Yes, the Oct. 9 and Oct. 21 visions ( of the C/2010 X1 remnant ) that
      then were planted in my brain still remain, crystal clear, similar to
      many previous estimates of very low DC "normal" comets with tail and no
      observable central condensation.

      Let's go to this ( complex ) subject.

      0 - Sorry for the extreme length of the text.

      1 - This will be my final post on these C/2010 X1 - and related -
      threads, like another kind of "silence": this subject is closed for me.
      I've been physically tired lately, under antibiotic treatment. I'm
      simply a visual observer, doing my work under mountain skies ... not
      wishing to go on forever into dialectical discussions.

      2 - Recent CBET 2876 ( including Sostero, Guido and Howes imaging
      efforts, visual photometry, and mainly, Sekanina's analysis on the
      comet's disintegration process ) gives a good resume of the actual
      knowledge about this final evolution of the comet.

      3 - I suppose that most members of this list are some kind of tired
      about this X1-related threads. I also suppose that many members are
      tired of my long posts ( so am I ...). We must remember that I didn't
      begin the long posts. I ONLY reported to the list what I thought were
      interesting observations. Some people can justifiably think that I'm
      seeking some notoriety. I can assure them that I'm not. At my near 60
      years of varied life I have near fulfilled almost all my life goals. I
      have had enough experiences ( including near death situations :
      exploring underground rivers in deep caves, mountain-climbing on ice,
      ..., potential severe accidents after hundreds of thousands of
      kilometers on the road ), and my actual perspective of life is familiar
      and quiet ... But including, of course, the serious observation of comets.

      ( sorry for this personal digression ).


      4 - Sincere thanks to Richard Miles for his very interesting
      contribution ( directly related to this thread ) on contrasting human
      vision and CCD cameras.
      These paragraphs are of the most pertinence and interest :

      >
      > Anyway, back to the pertinent point, it's this. People these days are so
      > used to using cameras and the like that they fall into the trap of
      thinking
      > the eye operates on the same principle as a camera or CCD. The truth is
      > that in many of its functions IT DOES NOT. Indeed it is the very
      mechanism
      > by which the eye works that makes it so valuable when estimating the
      > appearance and brightness of diffuse extended objects such as comets.
      > even larger areas but at the expense of gradually falling efficiency.]
      > ...
      >
      > A CCD camera is a difficult tool to use for measuring the integrated
      > intensity of an extended coma because as you use increasingly larger
      > measuring apertures, three effects work against you; (i) you add more
      noise,
      > (ii) larger areas contain increasing numbers of background stars, and
      (iii)
      > the same error in the measured background intensity leads to an
      increase in
      > the systematic errors in the final result.
      > ...
      > A well-trained visual observer can avoid these pitfalls of the CCD!
      > (btw: The recent work of Sostero, Guido and Howes on C/2010 X1
      > has been useful re. image background subtraction techniques for
      amateurs.)
      >
      > Advanced amateurs working visually have honed their observing
      techniques to
      > be near optimal.
      > ...
      > Here's how I'd sum up working at the optimal limit for
      > seeing a very extended coma from a physiological basis:
      >
      > (a) The telescope focal length and magnification should be such that the
      > apparent size of the coma in the eyepiece is kept as small as possible,
      > preferably no larger than about 2 degrees in size.
      > (b) Vision should be averted by about 30 deg from the fovea.
      > (c) The exit pupil at the eyepiece should be 3-5 mm in diameter.
      > (d) Scattered light should be reduced to a minimum to minimise the
      intensity
      > of the background sky.
      >
      > The subject of the apparent intensity of the background sky is also
      crucial
      >...
      > So if we take a real example, what would be the ideal scope to view the
      > remnant cloud of C/2010 X1? If we consider that the cloud has a minor
      axial
      > dimension of 4' (from the Oct 23 image of Sostero et al.) then the ideal
      > magnification to use would be 30x (i.e. 2deg/4'). So to fit that
      through a
      > 5mm pupil, the entrance aperture would need to be 150 mm across.
      >...
      > We can now see that JJGS's setup of 77x200mm was not so far from the
      ideal,
      > which would have been say 40x150mm. However, using a 400mm scope would
      > push the apparent size subtended by the coma well past the 2-degree
      criterion.
      >
      > Many comet observers have a range of scopes / binoculars of various
      size and
      > so the key is to select the instrument which is best suited to each
      target.
      >
      > Richard

      - Well, Richard, I ( almost ) can't add a single line to your extensive
      exposition. I only can give some additional information related with my
      Oct. 21 observation of C/2010 X1. Knowing from theory and experience
      this "near optimal" considerations, ( and based on my previous Oct. 9
      observation ), I've tried to observe the remnant with 25x100 binoculars,
      without positive results. I have also 40 and 56 mmm eyepieces, giving 50
      and 36x with my 20 cm SCT ( focal length: 2000 mm ). Both setups (
      25x100 binoculars and SCT at very low magnifications ) give a too high
      apparent intensity of the background sky, not allowing the observation
      of such a diffuse object.
      Besides, on this kind of situations, there is another very important
      factor : the brightness and distribution of the nearby field stars.
      Taking all this into account, on my Oct. 21.00 UT, a higher
      magnification ( like 77x ) was also needed for the detailed detection of
      the motion, the study of the morphology of the "tail-like" remnant and
      the sunward coma-like near-circular area with a slightly higher degree
      of condensation.


      5 - Thanks also to Jakub Cerny ... I obviously agree with the C/2010 X1
      section of his text to a great extent :


      >
      > 1) Statement that the JJ's observations from 21.10. is real but the 9.10.
      > one is not. For me it is pretty hard to believe that someone would construct
      > a dust cloud with "tail" extending in p.a. which was later been confirmed on
      > CCDs without knowin that. If that observation was not real then JJ must have
      > really luck in imagination ;-). I also think that while the comet was on
      > 9.10. more distant, the difference between cloud and comet nucleus expected
      > position should be smaller!
      >
      > We should not forget that the recovery of dust cloud using CCD was made
      > after big effort inspired by JJ's visual observations. TO me it looks
      > simply, that it was not recovered on 9.10. due people did not even tried to
      > find it with small instruments.


      6 - ... But I can't agree with other sections :


      > 3)rd issue does not have anything with C/2010 X1 but for me it is most
      > important. The case of "bright" visual comets C/2011 A3 and C/2011 M1.
      > Honestly, always when I recieve a visual observations from J.J. then I have
      > on my mind something like "oh my god, he went crazy" with those magnitudes.
      > Somehow, JJ's magnitudes are always something like 2 mag brighter than other
      > observers. The reason is unknown, it can be anything started with bad
      > methodology to some specifications of JJ's sight or conditions.
      >
      > ...
      >
      > The other comet - C/2011 M1 seems to me very similar to comet from past -
      > 177P/Barnard ! Extremely large, diffuse coma with low surface brightness and
      > almost no sign of central condensation.
      >
      > ...
      >
      > Alan you speaking about that you never had more then 0.5 mag difference to
      > other observers, but I know al ot of historical issues when there was
      > terrible differences in comet magnitudes! Always it was caused by large,
      > faint diffuse coma.
      >


      - Jakub, you've got exactly the point in this last paragraph : the
      "great" referred differences in the m1 estimates arise in the
      observations of comets showing large and diffuse comae with faint outer
      regions. I will be more explicit : ... especially for such kind of
      comets located at low altitude, like C/2011 A3 in my recent observation :

      C/2011 A3 (Gibbs):
      2011 Oct. 15.79 UT: m1=9.1, Dia.=8', DC=2, Tail: 0.6 deg. in PA 80 deg,
      20 cm SCT (77x), Juan Jose Gonzalez ( Aralla, alt. 1360 m., Leon, N.
      Spain ) [ Altitude: 15 deg. Mountain location, very clear sky.].

      I will rewrite now Jakub's text with some of my own words : Honestly,
      when I make a "bright" visual estimate like the C/2011 A3 recent one, I
      have on my mind something like "some people in the cometary community
      will think that I'm wrong ...".
      But, as previously and frequently said, as a physicist and observer, I
      must report the estimates exactly as they are.

      Here are some recent estimates from Comet_Obs site:

      C/2011 A3 (Gibbs):
      Oct. 15.79 UT, m1=9.1, Dia.=8', DC=2, 20cm SCT (77x), J. J. Gonzalez
      (Spain);
      Oct. 7.41, m1=[10.4, 40.0cm L (144x), Seiichi Yoshida (Japan);
      Oct. 02.76, m1=10.6, Dia.=2.3’, DC=3, 25 cm reflector (100x), S. Szabo
      (Hungary);
      Sep. 24.83, m1=9.7, Dia.=6', DC=2/, 20 cm SCT (77x), J.J.Gonzalez;
      Sep. 24.78, m1=11.0, Dia.=5'.0, DC=2/, 35 cm reflector (107x), J.Cerny
      (Czech Republic);
      Sep. 19.84, m1=9.7, Dia.=6', DC=2/, 20 cm SCT (77x), J.J.Gonzalez;
      Sep. 3.83, m1=10.9, Dia=2.2', DC=3, 20 cmL (100x), M.Paradowski ( Poland);
      Sep. 03.81, m1=11.2, Dia.=3'.8, DC=3/, 35 cm reflector (107x), J.Cerny;
      Aug. 28.94, m1=10.8:, Dia=2.5', DC=2, 22 cmL (160x), M.Goiato (Brasil);
      Aug. 28.83, m1=12.0, Dia.=2'.6, DC=4, 35 cm L (107x), J.Cerny;
      Aug. 26.88, m1=10.3, Dia.=6', DC=2/, 20 cm SCT (77x), J.J.Gonzalez;
      Aug. 26.84, m1=[11.3, Dia.=3'.5, 25x100 binoculars, J.Cerny;
      Aug. 25.84, m1=11.5, Dia.=3'.5, DC=3, 35 cm L (107x), J.Cerny.

      In such cases ( as C/2011 A3 ) of comets located at low altitude, as we
      knows, the elevation of the observing site, and local atmospheric
      conditions, have a great influence.

      Another "problematic, extremely diluted and fuzzy comet" is C/2011 M1 :

      C/2011 M1 (LINEAR):
      Sep. 25.19 UT, m1=9.5, Dia.=5', DC=2, 20 cm SCT (77x) J.J.Gonzalez (Spain).
      Sep. 07.18, m1=9.2, Dia.=8', DC=2, 20 cm SCT (77x), J.J.Gonzalez.
      Sep. 03.18, m1=9.2, Dia.=7', DC=2, 20 cm SCT (77x), J.J.Gonzalez.
      Aug. 27.09, m1=10.4, Dia.=6'.4, DC=2, 35 cm L (64x), J. Cerny (Czech
      Republic).
      Aug. 26.89, m1=9.5, Dia.=6', DC=2, 20 cm SCT (77x), J.J.Gonzalez.
      Aug. 26.86, m1=10.2, Dia.=5', DC=2, 23,5 cm SCT (77x), C. Labordena (Spain).
      Aug. 24.82, m1=13.0:, Dia.=2', DC=2, 50,8 cm L (117x). S. Szabo (Hungary).
      Aug. 20.83, m1=10.6, Dia=2.7', DC=3, 25x100 B, M. Paradowski (Poland).
      Aug. 19.86, m1=12.2 , Dia=1', DC=1, 32 cm L (120x), U. Pilz (Germany).

      I must explain here something about the geographic and atmospheric
      conditions of the Cantabrian Mountains, or "Cordillera Cantabrica". The
      most simple geographic data and images can be found on the Wikipedia.
      They extend for more than approximately 300 km across N. Spain, along
      the coast of the Cantabrian Sea. The northern slope of the range rises
      abruptly from near sea level. The descent of the southern slope to the
      high plateaux of Leon and Castilla is more gradual. Many peaks are over
      2000 m high, but the greatest altitudes are attained in the central
      section, on the borders of Asturias, Leon, Cantabria and Palencia. In
      this section rises the higher massif, "Picos de Europa", one of the
      greatest mountain limestone karsts of the world, topping at 2650 m. The
      Cantabrian Mountains make a sharp divide between "Green Spain" to the
      north, and the dry central plateau of the Iberian Peninsula. The north
      facing slopes receive frequently heavy cyclonic rainfall from the
      Cantabrian Sea, whereas the southern slopes are dryer, in rain shadow.
      The east - west alignment of the ridge, nearly parallel and close to the
      sea, explains some of the special atmospheric conditions, very favorable
      on clear days for the astronomical observations at low altitude towards
      the eastern and western horizons.

      Let's now come back to the comets ...

      - Jakub and friends, my estimates AREN'T ALWAYS something like 2 mag
      brighter than other observers.

      A very good ( among many other ) recent example with very large coma is
      103P/Hartley near maximum brightness:

      103P/Hartley:
      2010
      Oct. 22.15, 4.3, & 50' (J. Cerny, Senohraby, Czech Republic, 0.05-m
      refractor);
      21.36, 4.8, 40' (M. Goiato, Aracatuba, Brazil, 8x25 binoculars);
      21.31, 5.0, 30' (W. Souza, Sao Paulo, Brazil, 7x50 binoculars);
      20.98, 5.5, 50' (G. Pappa, Mascalucia, Italy, 12x50 binoculars);
      20.19, 4.7, 45' (J. J. Gonzalez, Leon, Spain, 4x30 monocular);
      19.45, 4.9, 45' (C. W. Hergenrother, Tucson, Arizona, 6x30 monocular);
      18.10, 4.6, 50' (J. J. Gonzalez, Leon, Spain, naked eye);
      16.92, 4.8, 40' (T. Scarmato, Calabria, Italy, 7x50 binoculars);
      15.00, 4.7, 60' (J. J. Gonzalez, Leon, Spain, naked eye);
      14.12, 5.0, 40' (M. Goiato, Brazil, 8x25 binoculars);
      14.11, 5.1, 50' (P. Horalek, Ustupky, Czech republic, naked eye);
      13.93, 5.0, 50' (J. J. Gonzalez, Leon, Spain, 4x30 monocular);
      13.93, 5.1, 45' (M. Lehky, Hradec Kralove, Czech Republic, naked eye);
      13.92, 5.0, & 45' (J. Cerny, Senohraby, Czech Republic, naked eye);
      13.86, 5.3, 60' (V. Nevski, Vitebsk, Belarus, naked eye);
      13.38, 5.5, 30' (C. W. Hergenrother, Tucson, Arizona, 10x50 binoculars);
      12.93, 5.1, 45' (M. Lehky, Hradec Kralove, Czech Republic, naked eye);
      12.93, 5.3, 35' (P. Horalek, Ustupky, Czech republic, naked eye);
      11.95, 5.3, 40' (M. Lehky, Hradec Kralove, Czech Republic, naked eye);
      11.91, 5.2, & 45' (J. Cerny, Senohraby, Czech Republic, 0.05-m refractor);
      11.34, 5.8, 30' (C. S. Morris, Fillmore, CA, U.S.A., 10x50 binoculars);
      10.93, 5.4, 30' (M. Lehky, Hradec Kralove, Czech Republic, naked eye);
      10.86, 5.6, 45' (P. Horalek, Ustupky, Czech republic, 11x70 binoculars);
      10.80, 5.9, & 25' (B. H. Granslo, Nittedal, Norway, 7x50 binoculars);
      10.80, 5.2, 30' (T. Karhula, Virsbo, Sweden, naked eye);
      10.79, 5.5, 40' (K. Hornoch, Ondrejov, Czech Republic, naked eye);

      ( selected from the ICQ site ). The data are self-explaining ...

      - Let's comment the second section of the paragraph :
      "Somehow, JJ's magnitudes are always something like 2 mag brighter than
      other observers. The reason is unknown, it can be anything started with
      bad methodology to some specifications of JJ's sight or conditions".
      Bad methodology ? quoting a well-known dialogue : This can't be serious
      ... I've dedicated many thousands of hours on hundreds of nights to the
      improvement of the methodology of observation, making estimates of all
      kind of comets ( bright and faint, very diffuse and near stellar, ...)
      with all kind of instruments ( naked eye, low magnification monoculars,
      little and big binoculars, telescopes ... ) ...

      Some specifications of my sight ? Well ... from childhood, I know that I
      have good far vision ( but not exceptional ).

      - But ... yes, I can comment an interesting detail about my eyes. After
      all those thousands of hours at the eyepiece, my left eye is slightly
      more trained for the observation of diffuse comets, and the right eye
      for the observation of high-DC faint comets.
      So, I can understand well the problems of some visual astronomers when
      observing ( or not observing ... ) large and diffuse comet's comae.


      7 - Dave Herald addresses a very interesting and controversial question :


      > There is another issue to keep in mind with visual observations. It is one thing to compare estimates of total magnitude – as there the object is clearly visible ‘to all’. But when you get into the area of whether or not a visual observer could actually see an object, you run into issues of credibility that can too easily be treated as personal. The fundamental problem is that an observer’s assertion that they can see an object fails the test of repeatability until others can also see it. That is, until others can see it, the situation reduces to one of whether or not you believe the observer – or (perhaps more correctly) whether you accept the attribution given by the observer to what they saw. In this regard, getting an image of an object is far more satisfactory, as ‘everyone’ can dissect the image in detail and for independent conclusions.
      >
      > Net result is (in my opinion) that while visual observations of objects that are ‘generally’ visible are valuable and reliable, visual observations involving the detection of objects that others can’t see are properly subject treated with scepticism – purely on the basis of the lack of independent ‘repeatability’ or other forms of independent verification.
      >
      >
      > Dave Herald


      - I agree with most of your exposition, Dave. In this thread, C/2010 X1
      remnant has been observed both visually and CCD-imaged.

      But ... in some cases, we only have some single observations. And yes,
      we must treat them with specticism. But they can be probably true if the
      observer is a reliable one. We have some well known historical cases in
      Astronomy, both positive and negative.
      An interesting case ( especially for us, spaniards ) is the discovery of
      the atmosphere of Titan. Searching in Google for "discovery of the
      atmosphere of Titan" gives two dates : 1908 ( visually by Comas Solá ),
      1944 ( spectropically by Kuiper ). There has been a long debate about
      this question ...


      8 - The mail from Nicolas Biver is short but interesting, as usual.

      This is a well addressed text :


      > ...
      >
      > I have also another concern about a kind of "race for the brightest estimate" of any comets: it may not be true (hopefully) but I feel like there is a trend to look for being the one that will "see" the comet beeing the brightest (I recently observed C/2009 P1 barely brighter than 7.5, but several are reported it brighter than 7). It may be a bias due to method or star catalog selection, and also a trend not so confirmed in full ICQ dataset...
      > ...
      >


      - Nicolas, I've had the same feeling many times from the beginning of
      the World Wide Web in the mid-1990s, and the related instant information
      availability. Let's hope that this possible "race for the brightest
      estimate" will stay at the lowest possible level, as incompatible with
      the correct methodology.


      9 - The longer and denser mail comes from Alan Hale, deserving detailed
      answers.


      > ...
      > First off, of course, there is now no doubt that a faint dust stream remnant
      > of C/2010 X1 does indeed continue to exist. I was certainly skeptical of
      > this, up until the time I saw Rolando Ligustri's image that he took on the
      > 22nd; but that image, and the other images that he and other observers have
      > taken since then, clearly demonstrate that this dust stream is there.
      > ...
      > Armed with this knowledge, and also the knowledge of what precisely to look
      > for, I made another attempt on the morning of October 24. I did in fact seem
      > to see a shapeless but extended "something" in about the expected position,
      > and moreover this "something" seemed to move westward at the expected rate.
      > This was an extreme borderline observation ...
      > ...
      > For what it's worth, I did attempt a brightness measurement by an extreme
      > defocusing of stars, and would say somewhere around m1 ~12: I agree with
      > John, though, that this is essentially meaningless -- for one thing, there
      > is no coma, and that is usually what is meant by a comet's brightness -- and
      > at best it refers to a shapeless, ill-defined portion of the tail remnant.
      > ...


      - Alan, I'm glad that you could observe the C/2010 X1 remnant. From my
      side, the only "problem" was your extreme skepticism towards my visual
      observations and estimates.

      Let's make now a thought experiment : we interchange our "roles" in this
      C/2010 X1 "affair". So, you would have made two observations of the
      comet on Oct. 9 and 21 with a 20 cm SCT, and I would have tried it with
      a 41 cm telescope, without positive results. What would have been my
      reaction ? I never would have doubts about your observations. Instead, I
      would have thought about the causes of my negative result : objective
      difficulty of observing such a diffuse object, different starfields on
      different nights, atmospheric conditions, personal equation of the
      observer, magnification, and so on.

      This would have been the same for me towards any other well-known
      observer of our cometary community. Like you have said, "I have high
      respect for all of you".

      ( Well, maybe I'm not such a "well-known observer" after all for some
      members of our community ... I obviously respect that ... In any case,
      I'll continue observing comets, as happy as always, till age put an end
      ... ).

      Let me express another related comment ( previously told ) about my
      feelings after such "difficult" observations like the C/2010 X1 one. I
      don't think then about some kind of objective personal achievement.
      Mainly, I feel privileged to be in the correct mountain place and time
      for observing the comet to which I've dedicated my efforts.


      > ...
      > For what it's worth, I did attempt a brightness measurement by an extreme
      > defocusing of stars, and would say somewhere around m1 ~12: I agree with
      > John, though, that this is essentially meaningless -- for one thing, there
      > is no coma, and that is usually what is meant by a comet's brightness -- and
      > at best it refers to a shapeless, ill-defined portion of the tail remnant.
      > ...


      - I can't agree on the "essentially meaningless" nature of the magnitude
      estimate on this case. From CBET 2876 : " ... The amount of the dust
      ejecta in the cloud of C/2010 X1 cannot be determined because of the
      lack of photometry. A very crude estimate of the total cross-sectional
      area of the dust particles is only provided by the visual magnitude 10.2
      ... the result is about 480 km2. The mass of the cloud comes out to be
      on the order of 10^(12) grams."


      > ...
      > Now, having reported all this, I would like to comment on some visual
      > cometary observations, not only of C/2010 X1 but some other comets, and in
      > general. While Juan Gonzalez has been a bit on the "hot seat" with his
      > reports of C/2010 X1 -- and I freely admit that I have been among his
      > doubters, and I will get to that in a moment -- my comments are directed
      > more towards the current community of comet observers in general. I will
      > occasionaly use the word "you," but, except in the specific case of the
      > recent observations of C/2010 X1, I am not referring to any observer in
      > particular.
      >
      > Before proceeding, I wish to reiterate something I said in an earlier post,
      > i.e., at no time do I mean anything personal about any individual. I
      > consider everyone here friends and colleagues, and I have high respect for
      > all of you. I am speaking strictly of the scientific observations involved,
      > as I would like to believe that the visual brightness (and morphology)
      > reports of comets continue to have scientific value. That requires, though,
      > that they be done correctly at all times.
      > ...


      - When you say "...While Juan Gonzalez has been a bit on the "hot seat"
      with his reports of C/2010 X1 ... my comments are directed more towards
      the current community of comet observers in general", I obviously agree
      with you, Alan, ... but you are referring to me ( directly or indirectly
      ) in many sections of your text : regarding C/2010 X1, C/2011 M1, C/2011
      A3, and the final sections.

      Well, in any case, for me like for you, "... At no time do I mean
      anything personal about any individual. I consider everyone here friends
      and colleagues, and I have high respect for all of you".


      > ...
      > Let's look at Juan's two recent reports of C/2010 X1. The first one, on
      > October 9, specifically refers to a "coma;" we now know that there is no
      > "coma" for this comet, and anything that might have been visible was not at
      > the ephemeris position, and Juan makes no mention of this. Furthermore, he
      > remarks that there was zodiacal light present (with which I will concur,
      > with my own unsuccessful observation attempt around that same time), and,
      > considering the extremely low surface brightness of the "tail remnant," any
      > kind of background lighting should have wiped it out completely. (Recall
      > that all the CCD images at that time showed nothing, or at best, an
      > extremely faint and uncertain fragment that may or may not have been real.)
      > And while I accept at face value Juan's comments about the clarity of the
      > atmosphere down to the horizon, at an altitude of 23 degrees you are still
      > looking through over 2.5 air masses, and you are going to be encountering a
      > non-trivial amount of extinction.
      > ...


      - Here is my estimate, Alan :

      C/2010 X1 :
      2011 Oct. 9.20 UT: m1=10.7, Dia.=6', DC=1/, Tail: 0.2 deg. in PA 310
      deg, 20 cm SCT (77x), Juan Jose Gonzalez ( Alto del Castro - Aralla,
      alt. 1720 m., Leon, N. Spain ).
      [ The coma appears large and very diffuse, without central condensation.
      Observation made from mountain location under very good seeing
      conditions. Nearby field stars checked in DSS. Zodiacal light. Altitude:
      23 deg.].

      Yes, I used the word "coma", only referred to the morphological
      similarity between the observed object and a "normal" DC=1/ comet. As in
      my Oct. 21 estimate, this "coma" ( located in the sunward extreme of the
      remnant ) was a "near-circular area with a slightly higher degree of
      condensation".


      > ...
      > The upshot here is that I must remain very skeptical of the October 9 report
      > as, all things considered, it is inconsistent with what the CCD images (both
      > then and now) have revealed.
      > ...
      >


      - Sorry, but obviously I can't agree on your skepticism and
      interpretation of the images.

      Supplementary information ( from a previous post ) : For me this case
      wasn't problematic or near the threshold of visual detection. It was a
      clear observation ( the atmospheric conditions in the Cantabrian
      Mountains were near optimal down to the line of horizon ) made in the
      course of a short observing session ( 1 hour approx. ) between moonset
      and the beginning of the morning astronomical twilight. Under such very
      good conditions, and besides C/2010 X1, my plan was to observe another
      four comets ( C/2010 G2, C/2011 S2, 49P, and 45P at low altitude ), so I
      only could dedicate approx. 10 min to the observation and magnitude
      estimate of C/2010 X1, at low magnification as necessary. I didn't check
      for the motion, given the short time-interval and the apparent lack of
      central condensation in such a large ( 6' ) coma. The geometric center
      of this coma was close to the MPC ephemeris position, with an error bar
      of ± 4'.


      > ...
      > The second observation, on October 21, does seem at face value to be
      > reasonably consistent with what the later images showed, although I note
      > that he reported one of his "bright areas" to be at the ephemeris position.
      > ...
      >


      - This is my another estimate :

      C/2010 X1 :
      2011 Oct. 21.00 UT: m1=10.2, Dia.=7', DC=1/, Tail: 0.4 deg. in PA 310
      deg, 20 cm SCT (77x), Juan Jose Gonzalez ( Alto del Castro - Aralla,
      alt. 1720 m ).
      [ The comet's remnant appears visually like a very diffuse tail-like
      morphology, observable for 0.4 deg along the major axis, showing two
      near-circular areas of similar brightness with a slightly higher degree
      of condensation and 7' of diameter. One of this areas, with geometric
      center located approximately at R.A.=8h00m.5, Decl.=+28o26'.0 ( Oct.
      21.00 UT ), was close to the ephemeris position. The other area's center
      was located at R.A.=7h59m.5, Decl.=+28o34'.5. The motion of both areas
      was followed for 40 minutes, being consistent with the
      ephemeris.Observation made before moonrise, from mountain location with
      very good seeing, under slightly better conditions than twelve days ago
      (Oct.9). Nearby field stars checked in DSS. Altitude: 16 deg.].

      I said then, clearly : One of this areas ... was close to the ephemeris
      position. ( NOT at the ephemeris position ).


      > ............................ The October 21 report is much less clear to me;
      > I do have some problems with it, which I've discussed, but on the other hand
      > it is consistent enough with the CCD images that I cannot simply dismiss it.
      > ...


      - Yes, Alan, my Oct. 21.00 UT report is consistent enough with the
      POSTERIOR CCD images.

      ( I wish to sincerely thank here Nick Howes comment : "Your visual
      observations are what inspired our team to keep trying to image Elenin").


      > ...
      > While I am not infallible, with this kind of track record it is
      > inconceivable to me that I could be looking *directly* at a 9th- or
      > 10th-magnitude comet, and *not* see it. Yet, if I am to believe some of the
      > reports that have been submitted in recent years, that is precisely the
      > case.
      > ...
      >


      - Alan, I have been looking *directly* at some 9th- or 10th-magnitude (
      or similar ) comets, and I *didn't* see them ...

      Some of them were large and diffuse comets that I've been observing some
      days before, at decreasing altitude, when approaching perihelion.
      In other cases, also related to diffuse comets, there were various
      factors : atmospheric conditions, elevation of the site, ...



      > ...
      > There are several examples I can cite, but I will focus on two recent
      > ones.
      >
      > We've already discussed C/2011 M1 to an extent. Some of you were
      > consistently reporting this comet to be as bright as m1 ~9-10, with a large,
      > diffuse coma, and yet, despite numerous search attempts, I never saw it. And
      > in this case, the CCD images backed me up ...
      > ...
      > Another example that I have not seen discussed here yet is C/2011 A3. Again,
      > several of you have reported this comet as being bright at m1 ~9-10 and with
      > a large coma, and, again, despite numerous attempts I have failed to see it.
      > (Other observers have privately informed me that they, too, have failed to
      > see it.) Once again, the CCD images back me up ...
      > ...
      >


      - C/2011 A3 and C/2011 M1 visual observations have been extensively
      debated before.

      Obviously, like you, I'm not infallible in my observations, but
      sincerely, is for me impossible to think that more than four well-known
      observers ( as J. Cerny, M. Goiato, C. Labordena, M. Paradowsky, U.
      Pilz, S. Szabo, ... ) can be wrong on each comet ( A3, M1 ).
      CCD images aren't ALWAYS an evidence against a visual observation, as
      the recent C/2010 X1 case demonstrate, and has been exposed somewhere
      before.


      > ...
      >
      > These are *not* cases of "visual photometry vs. CCD photometry;" these are
      > cases of CCD images showing what is and what isn't there. It is very
      > disingenuous to cite the CCD images as positive evidence of the C/2010 X1
      > observations, and then turn around and dismiss the CCD images of C/2011 M1
      > and C/2011 A3 which reveal that those two comets were much, much fainter
      > than the visual reports at the times in question.
      > ...
      >


      - Well, here is a clear disagreement. These ARE cases of the general
      "Visual vs. CCD" debate. Regarding the C/2010 X1, C/2011 A3 and C/2011
      M1 references, we obviously interpret them in different ways.


      > ...
      > There are two other issues I would like to touch upon. Back when they were
      > active, I was constantly cross-checking my observations against those of
      > John Bortle and Charles Morris, and I was almost always within a
      > half-magnitude or so of their reports. This doesn't necessarily mean that
      > any particular individual is "right," and, yes, we all should "call them as
      > we see them," but if everyone involved is doing it correctly, we should all
      > be seeing something fairly similar to each other. After all, if the depth of
      > a lake is 10 meters at a certain point, then all measurements of the depth
      > at that point should be somewhere close to 10 meters. Similarly, if a
      > comet's "true" brightness is magnitude 10.0, then all measurements should be
      > somewhat close to that (say, between magnitude 9.5 and 10.5).
      > ...
      >


      - First of all, my memory and greetings to Charles, valued friend.

      Alan, I remember well those times, after the beginning of the WWW in the
      mid-1990s. And I agree on the utility of that kind of cross-checking
      observations among experienced observers.

      But ... the problem of the m1 estimates and coma diameter of large and
      diffuse comets was and is always present.

      Only as a single example ( not a rule ... ) :

      45P/Honda-Mrkos-Pajdusakova:
      1996
      Feb. 14.39 UT: m1=7.5:, Dia.~25', DC=0...10x50 B....Charles Morris
      (Lockwood Valley, CA) [Just a brightening of the sky background ...
      difficult to estimate.]
      Feb. 16.42 UT: m1=8.3, Dia.=10', DC=0-1...10x50 B....Alan Hale
      (Cloudcroft, NM).
      ( From Charles website ... ).

      Another question ... What really means "comet's "true" brightness" ? In
      Physics and Astronomy we don't know the "true" value, we only have
      observed values ( and we can estimate errors ... ).

      As previously exposed, this is especially evident for the diffuse comets ...


      > ...
      > And then, there is the topic of limiting cometary magnitudes for telescopes
      > of various apertures. I have been utilizing the 41 cm telescope for over two
      > decades now, and can state with reasonable confidence that its limiting
      > magnitude for comets is around 14.5. (I'm referring to "cometary" comets,
      > not completely stellar ones, which I can obviously detect fainter.) Over the
      > years, observers I know with similar-sized telescopes have reported
      > something similar, and those with smaller or larger telescopes have reported
      > limiting magnitudes that are consistent with this.
      >
      > And yet nowadays, I am seeing some of you, including some of you with
      > telescopes significantly smaller than mine, routinely reporting comet
      > magnitudes up to a full magnitude -- sometimes even more -- fainter than the
      > limit of my telescope. How is this possible? ...
      > ...


      - The limiting "cometary" magnitude for the 20 cm SCT in my observations
      is close to 14.0-14.3 ( Henden photometry as reference ) for DC=5
      comets, under optimal atmospheric conditions.


      > ...
      > A question I would ask is, do you ever look for a comet and *not* see it? If
      > you're constantly looking for comets near the limit of your telescope, there
      > should be quite a few of them that you never see. If you somehow are able to
      > "see" every comet you attempt, then I submit that something is wrong. You
      > all know how many comets I have visually observed over the years, but you
      > may not know that there are over 200 other comets that I have looked for,
      > and *not* seen.
      > ...
      >


      - Yes, Alan, I frequently look for a comet and I don't see it. The
      limiting star magnitude for my 20 cm SCT is close to 15.3 ( Henden ), in
      good agreement with Roger Clark's data on "Visual Astronomy of the Deep
      Sky". Quite oftenly, I make negative attempts on comets on the 13.5 -
      15.0 range, depending upon particular conditions and situations.

      I'm not constantly looking for comets near the limit of my telescope. I
      know my limitations, and I know the limitations of
      my telescope. Don't have here the exact number, but in a good
      aproximation there are over 100 comets that I have looked for,
      and not seen.


      > ...
      > I guess I am reminded of the old story of the "boy who cried 'wolf.'" If you
      > consistently report 9th-magnitude comets that aren't there, report comet
      > brightnesses that are three magnitudes different from what I'm seeing, and
      > report seeing comets with a small telescope that are far too faint for me to
      > see with my larger telescope, then you will have to pardon my skepticism
      > when it comes to reports of extremely unusual cometary phenomena like what
      > we've recently seen with C/2010 X1. Even if you got it right this time . . .
      > ...
      >


      - Alan, sincerely I don't know if this text is more or less addressed to
      me ... But well, let's write for clarifying some questions :

      a ) I DON'T report 9-th magnitude comet's that aren't there ( like
      C/2011 A3, C/2011 M1, ... ). Some observers, depending upon particular
      conditions and situations, can observe these kind of diffuse comets, and
      others ( sometimes including myself ) can't observe them.

      b) I understand perfectly the normal skepticism regarding some reports
      about unusual cometary phenomena like C/2010 X1 post-perihelion
      evolution. This must be the scientific attitude.

      c) and d) You are putting yourself as as a kind of "standard" for the
      comparison of other observers with comments like "brightnesses that are
      three magnitudes different from what I'm seeing" and "seeing comets with
      a small telescope that are far too faint for me to see with my larger
      telescope". Is this really a "completely" scientific attitude ?


      > ...
      > The enthusiasm for visual comet observations that I am seeing now is
      > refreshing to see, and again, I really would like to think that the data we
      > obtain is scientifically useful. (It might even help in resolving the
      > "visual photometry vs. CCD photometry" issue, although I sometimes think
      > that's an unsolvable problem.) But it can only be useful if it's done right.
      > I implore everyone here -- veterans included, and that includes me -- to be
      > careful and cautious in obtaining these observations, and to see to it that
      > we are making the most reliable observations that we can possibly make.
      > ...


      - Fortunately, we are in complete agreement on this.


      10 - Finally, and sincerely, I hope that all these "C/2010 X1 threads"
      have been ( in some ways ) useful for the cometary community.


      Best regards from your old and tired friend,


      Juan Jose Gonzalez


      --------------------------------------------------------------------------
    • Uwe Pilz
      Dear Alan, dear Jakub, the German group has a very large archive of comet images. You find images of 2011M1 here (all by Michael Jäger):
      Message 2 of 24 , Oct 29, 2011
        Dear Alan, dear Jakub,

        the German group has a very large archive of comet images. You find images of
        2011M1 here (all by Michael Jäger):

        http://kometen.fg-vds.de/pix/2011M1_e.htm
        --
        Uwe Pilz

        On Fri 28/10/11 20:19 , Alan Hale ahale@... sent:
        > Dear Jakub,
        >
        > One of the C/2011 M1 images is here:
        >
        > http://www.fototime.com/ftweb/bin/ft.dll/picture?PictId={FB5D92
        > 0C-F948-4AA7-8F78-77EEEE1A1AD6}&size=ORIG
        >
        > Unfiltered CCD, total exposure time 15 minutes.
        >
        > Two others were taken by Michael Jaeger and posted to the comet-images
        > group, but they seem no longer to be there. I will e-mail those to you
        > privately.
        >
        > The C/2011 A3 images were e-mailed to me privately, and I will have to
        > askpermission to forward them along.
        >
        >
        > Sincerely,
        >
        > Alan
        >
        >
        >
        >
        > ------------------------------------
        >
        > 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-mlYahoo! Groups Links
        >
        > To visit your group on the web, go to:
        > http://groups.yahoo.com/group/comets-ml/
        > Your email settings:
        > Individual Email | Traditional
        >
        > To change settings online go to:
        > http://groups.yahoo.com/group/comets-ml/join(Yahoo! ID required)
        >
        > To change settings via email:
        > comets-ml-digest@yahoogroups.com comets-ml-fullfeatured@yahoogroups.com
        > To unsubscribe from this group, send an email to:
        > comets-ml-unsubscribe@yahoogroups.com
        > Your use of Yahoo! Groups is subject to:
        > http://docs.yahoo.com/info/terms/
        >
        >
        >

        Hol Dir das Notizbuch von uni.de: Schreibe dazu einen Artikel zum aktuellen Monatsthema und mit etwas Glück wird dein Artikel veröffentlicht. Alle Infos hier: http://uni.de/redaktion/nachwuchsjournalisten-gesucht
      • dfischer@astro.uni-bonn.de
        Wow, I m deeply impressed by the enthusiasm of the debaters in the Elenin et al. issue - have there ever been postings that long and detailled? To digest them
        Message 3 of 24 , Oct 29, 2011
          Wow, I'm deeply impressed by the enthusiasm of the debaters in the Elenin
          et al. issue - have there ever been postings that long and detailled? To
          digest them all would take more time than most probably have, so: Is there
          a kind - and impartial - soul who would take up the task to condense it
          all into one (open access) article one could then point others to?

          The question of what the - trained, experienced amateur's - eye can do
          with extended low surface brightness sky objects comes up quite
          frequently, esp. among visual deep sky enthusiasts, and I've witnessed
          pretty aggressive debates between some observers and their doubters.
          Perhaps deepening our understanding here a bit would be a fine legacy of
          comet Elenin, living longer than its dusty remains ...

          Dan

          http://cosmos4u.blogspot.com/2011/10/bright-spot-emerges-on-uranus-cam.html
          (see 2nd graf)
          http://www.oculum.de/newsletter/astro/100/40/8/148.ln1in.asp#2
          http://cosmos4u.blogspot.com/2011/10/comet-elenin-gone-for-good-though-some.html
        • Alan Hale
          Dear Juan, and all, I think I probably agree with Juan on one thing, i.e., the folks here at comets-ml may be getting a bit tired of the discussion, and one
          Message 4 of 24 , Oct 29, 2011
            Dear Juan, and all,

            I think I probably agree with Juan on one thing, i.e., the folks here at
            comets-ml may be getting a bit tired of the discussion, and one can only say
            the same things so many times before its gets tiresome. So this will likely
            be my last post on the subject, and to keep it at a reasonable length I will
            address one of Juan's points, and then share another one of my boring
            stories for the general community to ponder.


            Juan, you asked what the responses would be like if the roles were to be
            reversed. I'm not sure that's a valid question, because the roles would not
            be reversed in any strict sense.

            At the risk of belaboring something that's already been covered: I am
            confident enough in my observing skills that, if I were to report that there
            was a 9th-magnitude comet in a certain location, then everyone in this group
            -- not just some people, but *everyone* -- who had the necessary sky and
            weather conditions, any kind of decent telescope, and any observing
            experience whatsoever, could turn their telescopes to that location, and see
            a relatively bright comet that would be somewhere near 9th magnitude. Anyone
            on this group with imaging capability would record a relatively bright comet
            that would be consistent with a visual brightness of 9th magnitude. I
            wouldn't have to offer any hand-waving explanations as to why experienced
            members of this group couldn't see anything and why long-exposure CCD images
            only recorded an extremely faint and barely detectable smudge of light.

            As far as the C/2010 X1 remnant goes, all individual considerations aside,
            given all the evidence up until that point that nothing of this comet had
            survived, this was, at face value, an extraordinary observation. If I in
            fact had then seen something, even if I was sure I was seeing it -- which I
            highly doubt, since even though I have now "observed" this remnant on three
            different mornings, it is such a borderline detection that, in the absence
            of any recent images, I'm still not 100% sure I've seen anything -- I would
            not have posted on this group "I got it! I got it!" At most, I would have
            posted something like "I think I might have something here; could those of
            you with imaging capability try to confirm it?" I may not have posted
            anything at all, but rather privately e-mailed those who I know have the
            capability to confirm (or dis-confirm) my observation and awaited their
            results before going public.

            In fact, the face value nature of the observation was so extraordinary that
            I probably would have had an attitude something like the physicists from
            CERN who recently reported that they apparently detected neutrinos traveling
            faster than lightspeed. Note that they have openly invited skepticism and
            scrutiny of their results.

            I will end this segment of my post with a plea to those of you with imaging
            capability: I really would like to see more images!! Especially if you took
            any on the mornings of October 24, 26, and/or 28, so I can compare them with
            what I think I detected visually.


            And, now, to my story . . . I have debated with myself whether or not to
            share this with the group, and if so, when . . . but now I think the
            occasion is appropriate. Members of the group can take this however they
            wish.

            There was a time, back some years ago, when a somewhat younger version of
            myself was zealously and enthusiastically trying to track down as many
            comets as I could. I was using a 41 cm reflector (not the one I have now),
            and "seeing" everything I looked for, and submitting all my obsevations to
            the Central Bureau. It turns out that some of my submitted observations were
            rather "interesting" and "unusual," as they involved comets that had
            seemingly disintegrated before the times of my observations, and that some
            of my other observations were not consistent with what other, more
            experienced, observers were reporting.

            I received a letter -- this was in the days before e-mail -- from none other
            than Brian Marsden, who pointed out these facts to me, and who politely, but
            nevertheless sternly, suggested that I was trying too hard to "see" comets
            at the limit of my telescope. He politely, but nevertheless sternly,
            recommended that I exercise a little more care and caution in obtaining my
            observations.

            There were essentially two ways I could have responded. My initial
            temptation was to write Brian back and adamantly maintain that I had indeed
            seen all the comets I had reported, and provide some "explanations" as to
            why other observers weren't seeing these comets -- and then continued on
            doing what I was doing.

            But there was a second course of action I could have pursued. I could
            carefully consider what Brian had written, and carefully re-evaluate the
            observations I had made and submitted. Doing so would force me to have to
            admit that, yes, I had indeed been trying too hard to "see" comets that
            really weren't there (and among other things, this would require the removal
            of a couple of comets from my tally, which I was already keeping). Doing so
            would also require me to carefully redouble my efforts to ensure that any
            future observations I made and submitted were valid.

            I chose the second course of action, and wrote a letter back to Brian
            admitting my errors, and promising to exercise more care and caution in the
            future. As a result:

            A) I received a second letter from Brian. This one was also polite, but was
            not stern. Instead, it was warm and friendly, and he warmly and strongly
            encouraged me to continue making and submitting observations.

            B) I held true to my word, and from that point on did everything I could to
            ensure that I was making the best possible observations I could make, and no
            longer "seeing" comets just because I wanted to see them.

            C) Within a few years I had earned Brian's trust to the point where I was
            being asked to confirm comet discoveries for the Central Bureau.

            I somehow don't think these would have happened if I had decided to pursue
            the first course of action . . .


            Before closing, I would be remiss if I didn't mention that I had the good
            fortune to have frequent observing sessions with Charles Morris during the
            2 1/2 years we lived and worked near each other in southern California. We
            observed a lot of comets together; yes, we competed with each other, and,
            yes, we sometimes disagreed with and argued with each other, but I learned a
            tremendous amount from him, and there is no question that all those joint
            observing sessions in the southern California mountains during those 2 1/2
            years played a significant and huge role in helping to make me the
            experienced comet observer that I would like to think I am today.


            Sincerely,

            Alan
          • Josef Müller
            ... I took an image in the morning (at 2:45h UT) of Oktober 24. (SBIG ST-10XME - 130 mm Astrophysics f/6,4 - 4 exposures à 300 s)
            Message 5 of 24 , Oct 29, 2011
              Am 29.10.2011 19:38, schrieb Alan Hale:
              >
              > Dear Alan,
              >
              I took an image in the morning (at 2:45h UT) of Oktober 24.
              (SBIG ST-10XME - 130 mm Astrophysics f/6,4 - 4 exposures à 300 s)

              http://www.westerwald-astro.de/jjm/kometen/elenin-remnant.php?BackPath=kometen

              I hope I can help you!

              Sincerely,

              Josef Müller A21



              [Non-text portions of this message have been removed]
            • Alan Hale
              Dear Josef, Thank you! -- that does help quite a bit. Your image was taken a few hours before my observation, but the displacement of the brightest portion of
              Message 6 of 24 , Oct 29, 2011
                Dear Josef,

                Thank you! -- that does help quite a bit. Your image was taken a few hours
                before my observation, but the displacement of the brightest portion of the
                tail with respect to the comet's ephemeris position, as well as the location
                of the tail's northern "edge," is consistent with what I was seeing.


                Sincerely,

                Alan
              • Jakub Černý
                Dear Alan and all, This message is not adressed to you or JJ s or someone else, its simply to all of us (including me). Everyone have different motivation of
                Message 7 of 24 , Oct 29, 2011
                  Dear Alan and all,



                  This message is not adressed to you or JJ's or someone else, its simply to
                  all of us (including me).



                  Everyone have different motivation of why doing comet observations. Some
                  people like to see their names, others want as much comets as possibile. I
                  guess everyone have different story. Mine is that I have done my first comet
                  light curve analysis half year before first visual estimate, with
                  calculator, pencil and paper. That motivated me to observe comets even for
                  me it is not the main thing. I more likely analyzing data then observing,
                  however life at computer on seat is quite boring and I would die if I would
                  not be in contact with dark starry nights. But still my interest are most
                  accurate data to analyze, because without them, my work simply have no
                  point. But after 13 years of observing of almost 100 comets (without thoose
                  what I did not see, yes I also have some negative observations), my
                  experience tells me that everyone doing mistakes, including very experienced
                  observers. Where does new observers missing experience, the old one thinks
                  that they never can be wrong.



                  The visual observations will always contain bad observations, because it is
                  not very accurate and depends on observer, instrument, conditions and
                  technique! So much can do a big mess, thats why analysis can be serious only
                  if it contains a hughe number of observations. That is also reason why,
                  while I planning observations, I divide comets on thoose, who are bright and
                  good visible and the others thats near or under visible limit. The second
                  group I observing only sometimes. I know it can contain larger errors, thats
                  why I observing theese comets for example once or twice per month. Observing
                  brightest comets everyday is really boring.



                  As I am working with visual and CCDs data on daily basis, I do not see
                  anything surprising on thoose cases discussed. It is pretty normal that in
                  cases of large diffuse comets, that the magnitude spread of visual observers
                  can reach even 3 magnitudes. Also it is usual, that in case of condensed
                  comets the CCDs giving usually 1 mag fainter results then visual observers,
                  in the case of large diffuse comets, the difference is much larger. There is
                  also extremely difference when people doing "photometry" from astrometric
                  images. These must be done without saturated center of comets and result is
                  large loose of whole coma. Usually the astrometric magnitudes can produce
                  even 8 mag difference!





                  Because theese threads consumed so much time already I deciede to do some
                  deeper investigation. How does that observations fit the theory.



                  C/2011 A3 (Gibbs): I have found comets with most similar activity in near
                  same heliocentric distance (during its brightening) to be C/1998 T1, C/2003
                  T4 and C/2005 E2 with coma diameter 190 000, 150 000 and 90 000 km. With
                  median at 150 000.



                  The expected visible coma diameter according to this value gives 1.2' at
                  beginning of August and 1.1' at its end. With r ~ 2.7 AU, there is not
                  expected strong water production and the coma should be dominated with dust
                  with continuum peaking in red, favourable for CCD chips with best QE in red
                  or infrared. There is nothing excceding this values on many CCDs
                  http://astrosurf.com/cometas-obs/C2011A3/fotos.htm .



                  C/2011 M1 (LINEAR): I have found comets with most similar level of activity
                  in near same heliocentric distance (during its brightening) to be C/1998 U5,
                  C/1999 Jc, C/2011 OG108 and C/2007 W1 theese comets have max. coma diameter
                  275 000, 290 000, 100 000 and 400 000 km. with median at 282 500 km.



                  The expected visible coma diameter acording to this value it gives 5.1' at
                  beginning of August and 4.4' at its end. With r ~ 1 AU the comet should be
                  gas rich, therefore with magnitude peak in green, favourable for visual
                  observers. CCD observations confirming that inside coma continuing very
                  small activity of comet which may feed its coma with gas
                  (http://astrosurf.com/cometas-obs/C2011M1/fotos.htm ). However I suppose
                  further imagining of this comet using small apertures with low f/ and try
                  remove stars from background in order to improve S/N ratio.





                  Conclusions are clearly for me, the visual observations of C/2011 A3 (Gibbs)
                  with coma larger then 1' are theoreticly unreal (6' coma would need coma on
                  diameter near 800 000 km!). However the visual observing of C/2011 M1 with
                  large diffuse coma fitting theory well, maybe the observations excceding 5'
                  coma diameter may cause small overestimate of its m1.



                  Best regards,

                  Jakub Cerny



                  From: comets-ml@yahoogroups.com [mailto:comets-ml@yahoogroups.com] On Behalf
                  Of Alan Hale
                  Sent: Saturday, October 29, 2011 7:39 PM
                  To: comets-ml@yahoogroups.com
                  Subject: Re: [comets-ml] C/2010 X1 remnant, and other things.





                  Dear Juan, and all,

                  I think I probably agree with Juan on one thing, i.e., the folks here at
                  comets-ml may be getting a bit tired of the discussion, and one can only say
                  the same things so many times before its gets tiresome. So this will likely
                  be my last post on the subject, and to keep it at a reasonable length I will
                  address one of Juan's points, and then share another one of my boring
                  stories for the general community to ponder.

                  Juan, you asked what the responses would be like if the roles were to be
                  reversed. I'm not sure that's a valid question, because the roles would not
                  be reversed in any strict sense.

                  At the risk of belaboring something that's already been covered: I am
                  confident enough in my observing skills that, if I were to report that there
                  was a 9th-magnitude comet in a certain location, then everyone in this group
                  -- not just some people, but *everyone* -- who had the necessary sky and
                  weather conditions, any kind of decent telescope, and any observing
                  experience whatsoever, could turn their telescopes to that location, and see
                  a relatively bright comet that would be somewhere near 9th magnitude. Anyone
                  on this group with imaging capability would record a relatively bright comet
                  that would be consistent with a visual brightness of 9th magnitude. I y
                  wouldn't have to offer any hand-waving explanations as to why experienced
                  members of this group couldn't see anything and why long-exposure CCD images
                  only recorded an extremely faint and barely detectable smudge of light.

                  As far as the C/2010 X1 remnant goes, all individual considerations aside,
                  given all the evidence up until that point that nothing of this comet had
                  survived, this was, at face value, an extraordinary observation. If I in
                  fact had then seen something, even if I was sure I was seeing it -- which I
                  highly doubt, since even though I have now "observed" this remnant on three
                  different mornings, it is such a borderline detection that, in the absence
                  of any recent images, I'm still not 100% sure I've seen anything -- I would
                  not have posted on this group "I got it! I got it!" At most, I would have
                  posted something like "I think I might have something here; could those of
                  you with imaging capability try to confirm it?" I may not have posted
                  anything at all, but rather privately e-mailed those who I know have the
                  capability to confirm (or dis-confirm) my observation and awaited their
                  results before going public.

                  In fact, the face value nature of the observation was so extraordinary that
                  I probably would have had an attitude something like the physicists from
                  CERN who recently reported that they apparently detected neutrinos traveling
                  faster than lightspeed. Note that they have openly invited skepticism and
                  scrutiny of their results.

                  I will end this segment of my post with a plea to those of you with imaging
                  capability: I really would like to see more images!! Especially if you took
                  any on the mornings of October 24, 26, and/or 28, so I can compare them with
                  what I think I detected visually.

                  And, now, to my story . . . I have debated with myself whether or not to
                  share this with the group, and if so, when . . . but now I think the
                  occasion is appropriate. Members of the group can take this however they
                  wish.

                  There was a time, back some years ago, when a somewhat younger version of
                  myself was zealously and enthusiastically trying to track down as many
                  comets as I could. I was using a 41 cm reflector (not the one I have now),
                  and "seeing" everything I looked for, and submitting all my obsevations to
                  the Central Bureau. It turns out that some of my submitted observations were
                  rather "interesting" and "unusual," as they involved comets that had
                  seemingly disintegrated before the times of my observations, and that some
                  of my other observations were not consistent with what other, more
                  experienced, observers were reporting.

                  I received a letter -- this was in the days before e-mail -- from none other
                  than Brian Marsden, who pointed out these facts to me, and who politely, but
                  nevertheless sternly, suggested that I was trying too hard to "see" comets
                  at the limit of my telescope. He politely, but nevertheless sternly,
                  recommended that I exercise a little more care and caution in obtaining my
                  observations.

                  There were essentially two ways I could have responded. My initial
                  temptation was to write Brian back and adamantly maintain that I had indeed
                  seen all the comets I had reported, and provide some "explanations" as to
                  why other observers weren't seeing these comets -- and then continued on
                  doing what I was doing.

                  But there was a second course of action I could have pursued. I could
                  carefully consider what Brian had written, and carefully re-evaluate the
                  observations I had made and submitted. Doing so would force me to have to
                  admit that, yes, I had indeed been trying too hard to "see" comets that
                  really weren't there (and among other things, this would require the removal
                  of a couple of comets from my tally, which I was already keeping). Doing so
                  would also require me to carefully redouble my efforts to ensure that any
                  future observations I made and submitted were valid.

                  I chose the second course of action, and wrote a letter back to Brian
                  admitting my errors, and promising to exercise more care and caution in the
                  future. As a result:

                  A) I received a second letter from Brian. This one was also polite, but was
                  not stern. Instead, it was warm and friendly, and he warmly and strongly
                  encouraged me to continue making and submitting observations.

                  B) I held true to my word, and from that point on did everything I could to
                  ensure that I was making the best possible observations I could make, and no
                  longer "seeing" comets just because I wanted to see them.

                  C) Within a few years I had earned Brian's trust to the point where I was
                  being asked to confirm comet discoveries for the Central Bureau.

                  I somehow don't think these would have happened if I had decided to pursue
                  the first course of action . . .

                  Before closing, I would be remiss if I didn't mention that I had the good
                  fortune to have frequent observing sessions with Charles Morris during the
                  2 1/2 years we lived and worked near each other in southern California. We
                  observed a lot of comets together; yes, we competed with each other, and,
                  yes, we sometimes disagreed with and argued with each other, but I learned a
                  tremendous amount from him, and there is no question that all those joint
                  observing sessions in the southern California mountains during those 2 1/2
                  years played a significant and huge role in helping to make me the
                  experienced comet observer that I would like to think I am today.

                  Sincerely,

                  Alan





                  [Non-text portions of this message have been removed]
                • Alan Hale
                  Dear Jakub, While I had stated earlier that I had probably made my last post on the ... As I have repeatedly stated, I am not infallible, and I am constantly
                  Message 8 of 24 , Oct 29, 2011
                    Dear Jakub,

                    While I had stated earlier that I had probably made my last post on the
                    subject, I can't let this slide:

                    > experience tells me that everyone doing mistakes, including very experienced
                    > observers. Where does new observers missing experience, the old one thinks
                    > that they never can be wrong.
                    >

                    As I have repeatedly stated, I am not infallible, and I am constantly aware
                    of that when I make my observations. I posted earlier today an account of
                    some serious observing errors I once made, and I can post quite a few more
                    accounts if people would like.

                    But that being said, after four decades of visual comet observations, (with
                    a few years of CCD observing thrown in as well), and over two decades of
                    that chasing down comets to confirm for the Central Bureau, there is simply
                    *no* way that I can be looking *directly* at a 9th, 10th, 11th magnitude
                    comet, and *not* see it.


                    Sincerely,

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