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In short
Ketu is the Moon's descending node, counted as the ninth of the nine grahas in BPHS. This app places it exactly 180 degrees from Rahu, marks it retrograde, treats it as a natural malefic, and gives it the 7-year period that opens the Vimshottari sequence for births in Ashwini, Magha and Mula.
What the term means
Ketu is the point where the Moon's path crosses the Sun's path going south - the descending one of the two lunar nodes. Like Rahu it has no body, yet it is read as a graha. In this app Ketu is not computed on its own: it is always Rahu's longitude plus 180 degrees, so the two are always in opposite signs and opposite houses.
Where the term comes from
BPHS Ch. 3 Sl. 10 lists Ketu ninth and last of the grahas, and Sl. 11 counts it a malefic with Rahu. Sl. 30 describes Rahu at length and then says only that "Ketu is akin to Rahu". BPHS Ch. 47 Sl. 34-39½ gives Ketu exaltation in Vrischik, Mooltrikon in Dhanu and own sign in Vrischik, and records that some sages give it Meen instead. The Bhrigu Sutras identify Ketu as the descending node, say the nodes are always 180 degrees apart and always retrograde, and note that the ancients disagree about their signs (Part I, pp. 12-13).
How this app uses it
- Position: ketu = rahu + 180, from the mean node. Ketu's retrograde flag is set to true by convention, like Rahu's.
- Nature: Ketu is in the MALEFICS list (see papa graha) and casts only the 7th-house aspect.
- Dignity: there are no node rows in the dignity table, so the BPHS Ch. 47 signs are not applied and Ketu reads Neutral everywhere.
- Lordship: Ketu rules no sign in SIGN_LORDS. In the Chara Dasha it is Scorpio's second lord beside Mars, and the engine picks the stronger of the two.
- Timing: Ketu's Vimshottari period is 7 years. The engine's sequence starts from Ketu, so a Moon in Ashwini, Magha or Mula starts the timeline in a Ketu period.
One engine reading
For 19 January 1985, 11:14 IST, New Delhi, the engine places Ketu at Scorpio 0.54, Vishakha pada 4, in the 9th house - opposite Rahu at Taurus 0.54 in the 3rd.
Pages that use this term
- Ketu in Vedic astrology - the full page on the node.
- Ketu Mahadasha - the seven-year period.
- Ketu in the 12th house - one of the twelve house pages.
- Kaal Sarp Dosha explained - the axis Ketu forms with Rahu.
- Vimshottari Dasha calculator - shows where Ketu's period falls in your timeline.
Related terms
Mean node, Chhaya graha, Mahadasha and Vrishchika.