From there I tracked back to things like Isaac Azimov, Moon over Babylon which contains a good description of Planetary Hours--a concept in astrology--but like modern astrologers, he does not seem to know what the planetary hours were actually good for.  Realizing the import was a major breakthrough.  

Clues turn up here and there.  The Ballad of Thomas the Rhymer was one.  I was sitting in a concert at a Pagan Festival when I heard it performed for the first time.  I was astonished.  That was when the Planetary Hours clicked into place.  

In Richard Feynman's Surely You're Joking, Mr. Feynman he describes besting the archaeologists in a matter involving Mayan codices and astronomy--specifically picking out the 11959 day Mayan eclipse cycle.  Actually, the cycle of eclipses is 11960 days, and the one day discrepancy is a further hint.  

I spent a month surfing the net reading about the Mayan Calendar.  There is less there than you think.  Much drivel and absurdities.  But again, some good clues.  

But before all of this was cracking out an ordinary Astronomy text and making comparisons of planetary constants.  Ratios of synodic periods are the key.  Since, fortunately, the ancients had the same sky that we do, it is possible to know what they could observe.  They just thought about it differently.  

I will have to post a diary.  

Thanks for your compliment, and interest.  

The Fates are kind.