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Equinotial Marker HowTo
by Simon at 18:06 30/12/04 (Blogs::Simon)
I've been meaning to do a diagram like this for ages, and have finally got around to it. It's a graphical representation of how you can set up a basic calendar system to determine the equinox using only a stick, a mirror and any convenient marker stone on any single clear night of the year.

The inspiration for this is information contained in a book called "America BC" by Barry Fell.

Equinotial marker diagram

(Edited: Note that Polaris is used in the diagram to indicate 'true north', and ancient versions would need to use different reference points depending on epoch, due to precession)

From the book:

One day in 1874 a Reverend M. Gass, assisted by two students, was engaged in opening a small burial mound near Davenport, Iowa. Near the surface they found an intrusive Indian burial of obviously modern date but, as they descended deeper into the mound they began to uncover the skeletons of the persons for whom the mound had initially been raised. There were two adult skeletons, and a third skeleton of a child placed between them. Nearby they found an engraved tablet, now known as the Davenport Calendar Stele.

Photograph of Davenport Calendar Stele

This tablet carries an engraving consisting of a central scene surrounded by inscriptions in Egyptian, Iberian Punic and Libyan. The Iberian and Libyan texts both say that the outermost hieroglyphs contain the secret of how to regulate the calendar. The hieroglyphs themselves say (literally):

To a pillar attach a mirror so that at New Year the sun being in conjunction with the Ram in its house at the tilting of the balance in the Spring the Festival of celebration of the First of the Year and religious rites of the New Year are to take place when The Watcher stone at sunrise is illuminated by the sun. Star-watcher Priest of Osiris of the Libyan region.

Line tracing of Davenport Calendar Stele

The reference to a mirror is the key that I'd never previously encountered in any discussion about calendrical markers - but its use is obvious when you think about it, and the resulting geometry of the marker system is trivial.

This older article provides my textual description of the method used to set up the system.


GIF image (58 K) Diagram of equinotial marker setup
JPG image (72 K) Photograph of Davenport Calendar Stele
GIF image (52 K) Line tracing of Davenport Calendar Stele
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