The Tantra of Kalachakra is the basis of Tibetan astronomy. It explains some phenomena in a similar manner as modern astronomy science. Hence, Sun eclipse is described as the Moon passing between the Sun and the Earth.[dubious ][better source needed]
In 1318, the 3rd Karmapa received vision of Kalachakra which he used to introduce a revised system of astronomy and astrology named the "Tsurphu Tradition of Astrology" (Tibetan: Tsur-tsi) which is still used in the Karma Kagyu school for the calculation of the Tibetan calendar.