At the top center is Manjushri, holding an upraised sword in the right hand and a lotus stem to the heart with the left, the blossom supporting the Prajnaparamita book. Manjushri, the patron bodhisattva of astrology is seated on a lotus in vajra posture surrounded by a blue and orange nimbus. The central image is a yellow tortoise lying on the back with limbs extended holding staves with impaled corpses. At the center of the round belly is a circle of nine multi-coloured squares containing the 9 magic numbers (mewa gu). Surrounding that, on a dark blue wheel and brown background are the 8 triagrams, of Chinese origin. The outer circle of various colours represent the elements: wood, fire, iron, water and earth. Pictured within are the 12 animal figures of the 60 year cycle. Starting from the top green square on left and moving right are a hare, dragon, snake, horse, sheep, monkey, bird, dog, boar, mouse, ox and tiger. The Tibetan system of astrology derives from two main sources, the early Manjushri system and the later Kalachakra Tantra system.