ASTRONOMY IN VEDANGA JYOTHISHYA
There are many complex algorithms to be able to estimate the nakshatra, Parva etc starting from a linear count in Yuga when Winter solstice occurred with Sun and Moon at Shravishta.
i) There are ten Ayana’s or Solstices in a Yuga. Algorithm in RVJ8-9 provides the moon pointed Nakshathras at beginning of Solstice
ii) The Equinoxes of Visuvat’s are estimated by algorithm in RVJ31, YVJ23
iii) The Algorithm in YVJ11 provides Ritu or vedic season during Yuga
iv) The thiti at end of each Parva or paksha in a Yuga can be estimated by algorithm in YVJ13 and RVJ4
v) The nakshathra can be determined from algorithm in YVJ14
vi) Nakshathra fractions can be determined from RVJ10 and YVJ15
vii) Lagna with respect to Shravishta can be found using algorithm in YVJ16 and RVJ14
viii) Nakshathra at any Parva during Yuga can be found suing algorithm in YVJ14 and YVJ18. The abbreviations for nakshathra using phonetics make estimation easy.
Modeling errors in Vedanga Jyotishya from modern astronomical view point
Clearly a 3400-year-old mathematical model of sun-moon motion cannot have the precision of modern day models of sun-moon motion. Vedanga Jyotishya has an understanding of possible errors in its model and allows for corrections by observation.
1) Solar year of 366 days is a round off of what we now know as 365.24 etc
2) Solar and Lunar conjunction do occur every 1830 days. However use of this 1830-day cycle will shift the Solstice 4 to 5 days every Yuga. Lagadha was apparently aware of this.
3) Earth’s Precession of sun is not explicitly accounted for, and may or may not be known to Lagadha
4) Provision to correct error occurring over rounded Yuga to 366 days at the beginning of Yuga with leftover errors is implicit in Vedanga Jyotishya
5) Vedanga Jyotishya proposes linear moon time motion with equal angular motion of moon for Nakshatras, making all thiti’s equal. This is not true because of complex moon motion.