The Sun Treatise

"Mihira [Varahamihira] had the theoretical treatises of the Greeks (Yavanas) available to him, and from his style of interpretation, it appears that he was introducing new ideas—or at least ideas and words that were not common to both traditions—into his own works. It is certain that some of these ideas date to a time after Ptolemy." To refute this opinion, the strongest evidence seems to me to be the fact that Varahamihira a 6th-century Indian astronomer and polymath showed an ignorance of the precession of the equinoxes (the movement of the spring equinox), even though he was aware that in his own time, the southern solstice Dakshinayana; the sun's southernmost point occurred at the beginning of the zodiac sign of Cancer or in the Punarvasu lunar mansion Nakshatra, whereas in ancient times it occurred at the midpoint of the Ashlesha constellation.1 If he had been familiar with the works of Hipparchus or Ptolemy, he would have certainly accepted the precession of the equinoxes the slow, circular shifting of Earth's axis that changes which stars are visible at the equinoxes as they described it. This point was also not addressed by Brahmagupta the 7th-century mathematician who first defined rules for computing with zero, which reveals that until Brahmagupta’s time, the concept of the precession of the equinoxes had not troubled medieval Indian astronomers. This is despite the fact that through direct observation of the sky in ancient times, they had realized that the constellations associated with the northern solstice Uttarayana and southern solstice had changed. We know this because the Maitrayani Upanishad mentions that the southern solstice occurred when the sun was between the Magha constellation and the middle of Dhanishta, and the northern solstice occurred when the sun was between the middle of Shravishtha and Ashlesha. In the Vedanga Jyotisha one of the oldest Indian texts on astronomy, used to time rituals as well, it is clearly stated that the northern solstice began when the sun entered the beginning of Shravishtha. Discussing this very shift, Varahamihira explains that in our time, the southern solstice occurs in Punarvasu; if it should differ from this in the future, one must determine it through direct observation.2

From the figures mentioned above, it is clear that the Indian values for the sidereal year the time it takes for the Sun to return to the same position relative to the stars are no more than 3 minutes and 27 seconds longer than the actual physical sidereal year, and Brahmagupta’s calculation is the closest of all. In reality, this value is about one and a quarter minutes less than the value of the anomalistic year manda-kendra varsha; the time between the Earth's successive closest approaches to the Sun, meaning it almost perfectly matches it. This is the reason why the motion of the solar apogee mandochcha; the point where the sun is farthest from the Earth is considered almost negligible in our texts. In comparison, there is a greater degree of error in the sidereal year values used by Meton a 5th-century BCE Greek astronomer and in Babylonia. The values for the tropical year sayan varsha; the year measured by the cycle of seasons given by Ptolemy and Kepler are 6.5 or 7 minutes greater than the actual tropical year. Therefore—

1. original: "आश्लेषार्द्धादासीद्यदा निवृत्तिः किलोष्णकिरणस्य । युक्तमयनं तदासीत् साम्प्रतमयनं पुनर्वसुतः ॥२१॥" translation: "When the return of the sun once occurred from the middle of Ashlesha, that solstice was then correct; currently, the solstice occurs from Punarvasu." — Brihat Samhita, Verse 21
2. Varahi Samhita, chapter on the Sun’s motion, pages 16, 17; Vigyanbhashya, page 336.