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    Re: Ecliptic, zodiac and history
    From: John Huth
    Date: 2010 Dec 11, 16:41 -0500
    Whoops - the firmament moves westward  - I was distracted.   My apologies - that must've been confusing.

    On Sat, Dec 11, 2010 at 4:34 PM, Apache Runner <apacherunner@gmail.com> wrote:
    Ever wonder how we got 12 hours in the day or night?   Neugebauer traces it to Egyptian partitioning of the sky and times of night based on the passage star clusters.   It's a bit involved, and I have to confess to not having read his original work, but this was how it was explained to me by a friend who is a fan of the history of astronomy.  

    Now, you might ask what this has to do with the ecliptic.    The passage of time throughout the year (ie. a calendar) can be marked by the heliacal rising of stars.   That is to say, just before dawn, you can see a star rise. Given even something as crude as a clepsydra, you can measure a time that it reaches some angle where it's visible, and then find the time to sunrise, which comes next.   There's both an altitude and azimuth of that star that you can effectively measure with respect to the Sun from the heliacal rising and if you track this over the course of the year, and know that the overall "firmament" moves eastward at 360/365.24 days, you can trace out the path of the ecliptic.   



    On Sat, Dec 11, 2010 at 4:05 PM, Bill <billyrem42@earthlink.net> wrote:
    On 12/11/10 2:01 PM, Apache Runner wrote:...

    Thank you for your answers.

    I fear, despite my setup, my question became, "...how the heck did they figure out the ecliptic so long ago?"

    Given hindsight and the wealth of information available at my fingertips, I can wrap my head around discovering and mapping the ecliptic.

    What still puzzles me, given the zodiac is placed along the ecliptic (ignoring precession), how were they able to marry the ecliptic (using the path of the the sun through the stars as a definition of ecliptic) and star background almost 3000 years ago--800 to 1100 years prior to Ptolemy or Hipparchus? Obviously they could not view the Sun and stars simultaneously.

    For example:  It is noon on any given day, the sun directly south at XX degrees above the horizon.  If it were not for the sun, what star pattern would I see?

    Bill B.


    Bill -

    A few more items - here's a build-it-yourself Stonehenge website:

    http://www.christiaan.com/stonehenge/index.php?pg=stonehenge-build-your-own-stonehenge

    The history of the precession of the equinoxes in the west is a bit
    murky.   It's often attributed to Hipparchus, but he left no writings.
    It was pushed by Ptolemy.    Supposedly, the longitude of bright stars
    were measured over some time period and shown to shift relative to the
    equinox, with comparisons of data over about 150 years - long enough to
    make significant observations - that is to say, the shift is enough to
    be detectable.   Another method is timing the difference between a
    tropical and sidereal year which is interesting because you (well, I in
    any case) have to think through how this was done.


     Neugebauer proposed that the Babylonians knew about the precession.

    Somewhat tangentially, but perhaps related - some of my students built a
    clepsydra out of spare parts and tested it out as a mapping device (e.g.
    comparing longitudes of distant cities).    It was an interesting
    project, and I wish they'd been a bit more ingenious about it, but I
    think with some effort, one can build one that's reasonably accurate.

    On Sat, Dec 11, 2010 at 9:23 AM, Apache Runner <apacherunner@gmail.com
    <mailto:apacherunner@gmail.com>> wrote:

       The easiest way to do it is to chart the sunrise/sunset location
       against markers lying on the horizon.    Historically, you can find
       things like the Hopi sun calendar, or orientation of grave barrows
       in northern Europe.  The discussion of  astronomical alignments of
       places like Stonehenge seem to still be in flux, but there are
       pointers to the path of the ecliptic.    With decent markers on the
       horizon, you can see when the Sun appears to "stand still" against
       the markers at the solstices.  (Sostice = "sun stop")

       A more interesting issue is the knowledge of cycles of the Moon -
       the Saros cycle for example.    People would have to wait 18+ years
       to accumulate information from one eclipse to the next (18 years,
       11.3 days between lunar eclipses).   Half a year is nothing compared
       to figuring out eclipses.



       On Sat, Dec 11, 2010 at 1:10 AM, Bill <billyrem42@earthlink.net
       <mailto:billyrem42@earthlink.net>> wrote:

           I am guessing when I get an answer to my question, I'll slap
           myself on the forehead and utter, "Of course." But here goes.

           I look at star charts and planispheres with the current
           ecliptic--the path of the sun through the stars--neatly added. I
           take it for granted that if I could see the stars and the Sun
           simultaneously that is the relationship I would see. Easy to
           confirm with an almanac and spherical trig.

           The zodiac signs--a form of right ascension or SHA--lie along
           the ecliptic as opposed to the celestial equator. The zodiac
           etc. have been around for about 3000 years, spanning the
           Sumerian's lunar calendar, the Babylonians, and the sexagesimal
           system. The shift of the First Point of Aries to its present
           location on the celestial equator also appears to indicate a
           long history of ecliptic knowledge.

           My question, how the heck did they figure out the ecliptic so
           long ago?  No pi, no trig.  A viewer would have to wait half a
           year to see the star pattern that would have that day's Sun
           superimposed on it. Yes?  A lunar calendar with 12 cycles a year
           and a leap month every three years would not be a big help.

           Bill B.






    --
    Keeping up with the grind



    --
    Keeping up with the grind
       
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