DERIVATION OF MEAN LONGITUDE That is to say, mean longitude of a planet in revolutions (revolution-number of the planet) × (ahargana) civil days in a yuga A rule for deriving the mean longitude of a planet from that of the Sun: 9. Reduce the Sun's mean longitude (given in terms of signs, degrees, and minutes) together with the years elapsed (treated as revolutions) to minutes of arc. Multiply them by the planet's own revolution-number stated in the Gitika¹ and divide (the product) by the number of (solar) years in a yuga. The result, say (the learned), is the planet's mean longitude in terms of minutes. That is to say, mean longitude of a planet in terms of minutes · 7 (Sun's mean longitude in revolutions etc. reduced to minutes) > (planet's revolution-number) Sun's revolution-number A rule for deriving the mean longitude of a planet from the mean longitude of the Moon or a planet or the ucca of a planet. 10. The (mean) longitude of the Moon, the planet, or the ucca (whichever is known) together with the revolutions per- formed should be reduced to minutes. The resulting minutes should then be multiplied by the revolution-number of the desired planet and (the product obtained should be) divided by the revolution-number of that (known) planet. The result is (the mean longitude of the desired planet) in terms of minutes.² ¹ This is the name of the first chapter of the Aryabhatiya. This rule occurs also in BrSpSi, xiii. 27; ŚiDVṛ, I, i. 30 (i); Siśe, ii, 25-26: SiŚi, I, i (c). 14 (i).
