Vimshottari dasha

Vimshottari is a timetable of periods, called dashas, each ruled by one of nine grahas, which add up to 120 years. Counting from Ashvini, the order is Ketu 7 years, Venus 20, the Sun 6, the Moon 10, Mars 7, Rahu 18, Jupiter 16, Saturn 19 and Mercury 17. Iyer's note in the 1905 edition of the Brihat Jataka lists the same nine in the order Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury, Ketu, Venus, which is the same cycle entered at a different point.

The Moon's nakshatra decides where the timetable starts. Each lord rules three nakshatras nine places apart, so Ashvini, Magha and Mula belong to Ketu while Krittika, Uttara Phalguni and Uttara Ashadha belong to the Sun. The typed Sanskrit of the Brihat Parashara Hora Shastra on Wikisource, edition unidentified, counts from Krittika and takes the remainder after dividing by nine, and Iyer gives the unspent part of the first period as the share of the nakshatra the Moon has still to cross, a rough rule by his own account. None of the sources read fixes the length of a dasha year: Iyer's example speaks of savana and soura years, and the Brihat Parashara Hora Shastra gives no length. The calculator uses a 365.25-day year, which is a convention of this site.

Vimshottari is not Varahamihira's own scheme. The quoted sentence is Iyer's comment on the system of dashas in the Brihat Jataka itself, and he says that Indian astrologers instead use the simple nakshatra dashas, the Udu dashas. In the sources read here, the 120-year table first appears in Iyer's translator's note and in chapter 46 of the typed Brihat Parashara Hora Shastra.

That chapter lists many dasha systems, among them Ashtottari, and calls Vimshottari the chief, with the further statement that in the Kali age it is the principal one. It sets conditions only for the other systems, for example Ashtottari when Rahu stands in an angle or triangle from the lord of the Lagna, and none that limits Vimshottari. A 1912 translator wrote that Vimshottari prevailed in the Deccan and the United Provinces and Ashtottari in Bengal, where Vimshottari was also gaining ground. The typed text gives Mercury 19 years, a total of 122 that contradicts its own 120, while Iyer and the 1912 translator give 17.