Vimshottari Dasha

The system divides a notional human span of a hundred and twenty years among the nine grahas in a fixed sequence with fixed lengths: Ketu seven years, Venus twenty, the Sun six, the Moon ten, Mars seven, Rahu eighteen, Jupiter sixteen, Saturn nineteen and Mercury seventeen. The nine add to a hundred and twenty exactly, and the order never varies. What varies is where in the cycle a life begins.

That entry point is set by the Moon. The twenty seven nakshatras, the lunar mansions the ecliptic is divided into, are assigned to the nine planets three times over in the same order, so the mansion the Moon occupies at birth names the ruler of the first period, and the Moon's position within that mansion fixes how much of the period has already elapsed. Two charts with every planet in the same degree but the Moon a fraction of a mansion apart can therefore run entirely different timelines.

Each major period is subdivided into nine sub periods in the same proportions and the same order, and the subdivision can be carried further, three, four or five levels deep. Readings taken at that depth resolve to weeks. The name comes from the Sanskrit for a hundred and twenty, which is the one thing about the system that is not open to variation.

Vimshottari is the period system in general use, but it is not the only one the Sanskrit literature contains. Ashtottari runs to a hundred and eight years, Yogini to thirty six, and there are schemes tied to the sign rather than to the lunar mansion, along with a Kalachakra dasha that takes its divisions from a different geometry again. Classical texts discuss which system suits which chart, and the question is a live one in the commentarial literature rather than a settled matter.

The Brihat Parashara Hora Shastra, the large compendium attributed to the sage Parashara, is the text most often cited for Vimshottari and sets out the sequence and the subdivisions. The date and composition history of the work as it is printed today are debated, and the atlas records that rather than assigning it an age it cannot support.

David Pingree's survey of the Sanskrit astral literature is the standard guide to how this body of writing is organised and how it developed, including the substantial layer that entered from Greek astrology in the early centuries of the common era. The period systems are not part of that borrowed layer. Whatever their origin, they are among the features that make the Indian tradition's handling of time distinct from the Hellenistic material it otherwise absorbed so thoroughly.