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Just like Bill, I feel much in awe of the intellectual power of the people,
Babylonians and then Greeks, who assembled a mind-picture of the sky.

The notion of being able to say something as simple as "The Sun is in
Taurus", at a particular time of the year, when the Sun and Taurus can
never be seen together, calls for a lot of mental agility.

I imagine the development went a bit like this. Only a fraction of the
zodiacal stars can be seen on any night, but watching the constellations
pass each night over the year, shows that they join up again where they
started, so allows a inverted "bowl" to be constructed (in the mind,
anyway) that goes right around. That provides the background for the Sun's
path around the zodiac.

And then, as John Huth (Apache Runner) points out, stars rising heliacally
(rising just before dawn before being then blotted out by the sunlight),
and corresponding stars setting, mark the passage of the year, and these
are the stars that are closest to the Sun (in ecliptic longitude), at that
date, that can just be seen. So, you might estimate the angle between the
not-yet-risen Sun and the star at its final twinkle before sunrise, which
then helps to place the Sun with respect to the zodiacal stars..

But I suspect the biggest part in this evolving mind-picture was played by
the Moon, because of the way it could link the Sun and the stars, and
because it always kept pretty close to the Sun's path around the zodiac. If
you could estimate the angle between Sun and Moon, on a day they could both
be seen, and then the following night note where the Moon was against the
stars, allowing for the Moon's motion as fine-tuning, that allowed the Sun
to be mapped against the stars.

It must have called for a lot of mental contortion and argument, with
diagrams drawn with sticks in the sand, when these geometrical schools got
together in the Greek equivalent of Navlist. I can imagine it now.

And I think we need to distinguish between the Greeks and the Babylonians.
The Babylonians made superb observations, and kept detailed records, which
were invaluable to later astronomers, but they don't seem to have been at
all interested in understanding what was going on. Their aim seems simply
to be able to predict the future (such as eclipses) for the purpose of
deducing omens for their rulers. But the Greeks were another matter,
showing great intellectal curiosity. They built on the Babylonian records
and their own, to create a magnificent system  which lasted until
Copernicus showed it to be largely nonsense.

A crowning achievement was the discovery of precession of the equinoxes,
which could have been Hipparchus' work, but then later Ptolemy got its rate
quite badly wrong, which created problems for later astronomers right up to
the renaissance.

George.

contact George Huxtable, at george{at}hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


----- Original Message -----
From: "Bill" 
To: 
Sent: Saturday, December 11, 2010 9:05 PM
Subject: [NavList] Re: Ecliptic, zodiac and history


| 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  > 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      > 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.
|
|
|

   

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