The 13th sign seems to be The Serpent Bearer, Ophiuchus. So, there seems to be a connection to reptilians. Note the illustration of the Staff of Aesculapius. Regarding the staff: I've read somewhere a while ago, this symbol stands for Kundalini, The snakes are the Ida and Pingala Nadi spiraling around the spine. I don't know, maybe this explaination is a cover-up.
http://starsandcoffee.christian-astrono … #ophiuchus
A 13-month calender would make much more sense to me. The months would perfectly fit to the moon cycles (28 days). The word month derives obviously from "moon" So, it is illogical to have a calendar that causes the moon-cycles to be out of sync to the month lengths. Maybe that is the reason - to get people out of sync of their natural cycles. A problem could be, 13 x 28 sums up 364.
A man is born gentle and weak. At his death he is hard and stiff.
Green plants are tender and filled with sap. At their death they are withered and dry.
Therefore the stiff and unbending is the disciple of death. The gentle and yielding is the disciple of life.