Indian Chronology (Solar, Lunar and Planetary): A Practical Guide to the Interpretation and Verification of Tithis, Nakshatras, Horoscopes and other Indian Time-records, B.C. 1 to A.D. 2000 c14.12

c14.12

64. Now, how are we to determine the sun's tropical longitude? The longitude that is given by the day of the Indian solar year is a sidereal longitude, *i.e.*, the longitude of the sun measured from a fixed point of the ecliptic, which fixed point was the true vernal equinox about A.D. 500 or Kaliyuga 3600. Every year since then, the vernal equinox has been moving further and further away from that fixed point, and the sun's tropical longitude for any year subsequent to 3600 Kaliyuga must be found by adding to his sidereal longitude 3 degrees for every subsequent period of 200 years.* In this portion of our treatise degrees are always converted into days, and for the purpose of Sūrya Siddhānta tithis, the tropical longitude for any day in any year is determined by adding to the day of the solar year 1 day for every 64 years expired since 3740 Kaliyuga (A.D. 639). Other Siddhāntas give the precession as 1 day for every 60 years, which is more correct than 1 day for every 64 years (see Sec. 277).