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In short
The lunar nodes are the two points where the Moon's apparent path crosses the Sun's: the northward crossing is Rahu and the southward crossing Ketu, always 180 degrees apart. This app computes Rahu as the mean node, places Ketu opposite it, and marks both retrograde because the nodes move backwards through the zodiac.
What the term means
The Moon's orbit is tilted against the Sun's apparent path, so the two cross at two points on opposite sides of the sky. These are the lunar nodes. The one the Moon passes going north is the ascending node, Rahu; the one it passes going south is the descending node, Ketu. They are points, not bodies, and several of BPHS's lists - the exaltation degrees of Ch. 3 Sl. 49-50, for one - cover only the seven grahas from Surya to Shani.
Where the term comes from
BPHS itself names Rahu and Ketu as grahas, and its English translation glosses them in Ch. 3 Sl. 11 as "the ascending and the descending nodes" of the Moon. The geometry is set out in the Bhrigu Sutras (Part I, pp. 12-13): the two paths are inclined to each other by about 5 degrees, the crossings are 180 degrees apart, the northward crossing is Rahu, and the nodes move backwards through the zodiac at 19 degrees 20 minutes a year, staying in a sign for about 18 months.
How this app uses it
- One model, everywhere: astronomy.js computes the mean node - the smoothed average position - and every chart, transit and dasha reads that same Rahu. Ketu is Rahu plus 180 degrees.
- Backwards motion: both nodes carry a retrograde flag set to true by convention. Run on 1 January 2000 and 1 January 2001, the engine's sidereal mean node moved 19.40 degrees backwards in that year, close to the Bhrigu Sutras' figure.
- The true node as a check: trueNodeOffset() computes how far the true node sits from the mean one. It never moves Rahu; the Kaal Sarp calculator uses it only to say whether its verdict would change on the true node.
- The axis: Kaal Sarp asks whether all seven other grahas fall on one side of the Rahu-Ketu line.
Pages that use this term
- Rahu in Vedic astrology - the ascending node as a graha.
- Ketu in Vedic astrology - the descending node as a graha.
- Kaal Sarp Dosha explained - the nodal axis test and the mean-versus-true check.
- Rahu transit in Aries - one of the node's sign transits, with Ketu opposite.
- Kaal Sarp Dosha calculator - reads your chart against the axis.
- Gochar calculator - current Rahu and Ketu signs counted from your Moon.
Related terms
Chhaya graha, Vakri, Graha and Ephemeris.