
About Celtic Astrology
The Celtic zodiac is based on the cycle of the moon with the year divided into 13 lunar months, each associated with a tree considered to be sacred to the Druids.
The Druids believed the human race originally descended from the trees and each tree has particular magical qualities. They encoded these mysteries in a secret Shamanic alphabet, known as the Ogham, the origin of which is ascribed to Ogma, the Celtic god of poetry.
The 13 tree months each correspond to a tree, a letter of the Ogham alphabet, a guardian animal and a Celtic god.
This chart provides all information, as well as a detailed character analysis for each of the 13 personality types. It is especially interesting to compare the Celtic moon cycles with the traditional zodiac sun cycle.

Dimensions: inches / cm: 18.0 x 13.2" / 48 x 33cm.
I find that having this is useful as a reference.