Ketu Dasha

The Ketu Mahadasha is the first period in the Vimshottari dasha, the principal system of planetary periods in jyotisha. Vimshottari means one hundred and twenty, the total span in years of the full cycle, divided among the nine grahas in a fixed sequence. Which period a person is born into is set by the nakshatra the Moon occupies at birth, and the sequence then runs Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury. Ketu's period lasts seven years. As the south node and the significator of detachment, loss, and spirituality, its dasha is traditionally read as a time of endings, letting go, sudden turns, and inward or spiritual reorientation, coloured throughout by Ketu's karmic nature. These are the interpretive conventions of the tradition; the system is a mathematical timing scheme keyed to the Moon's birth nakshatra.

Within each mahadasha the same nine grahas recur as shorter antardasha, or bhukti, sub-periods, always beginning with the mahadasha lord's own antardasha and then proceeding through the standard sequence, Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury, from that starting point. The length of each antardasha is proportional: it is found by multiplying the mahadasha's total years by the antardasha lord's own Vimshottari years and dividing by one hundred and twenty, so the nine antardashas within a mahadasha always sum exactly back to that mahadasha's length. A seven-year Ketu Mahadasha therefore opens with a Ketu-Ketu antardasha of only about five months, seven times seven divided by one hundred and twenty in years, before moving to the longer Ketu-Venus stretch. The same proportional method is applied recursively to divide antardashas into still finer pratyantardashas.

This period runs seven years of the 120 that the Vimshottari cycle divides among the nine grahas, and a life enters it at birth if the Moon stood in one of its lord's three nakshatras, Ashwini, Magha and Mula.

The order of the nine periods is fixed and does not vary: Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury, and then Ketu again. It is the same order in which the nine grahas own the twenty-seven nakshatras, running three times through the list, which is what ties the dasha sequence to the Moon's position at birth. The nakshatra the Moon occupied gives the period a life begins in, and the fraction of that nakshatra already traversed gives how much of the period has already elapsed.

Each major period is subdivided in the same order and in the same proportions. A mahadasha is divided into nine antardashas, each running for the same fraction of it that its lord's own period bears to the whole 120 years, and the subdivision can be carried further into pratyantardashas and beyond. That is how the system produces timing fine enough to be tested: a combination in a chart is expected to show during the period and subperiod of the planets that form it.

Ketu opens the list as the tradition states it, which is a convention of presentation rather than a claim that any life begins there. A life begins in whichever period the Moon's nakshatra assigns, and all nine are equally likely at birth in proportion to their lengths.