Astronomy

Āryabhaṭīya, Gītikā 1 (499 CE) fixes the Earth's eastward rotations per yuga at 1,582,237,500 against 4,320,000 solar revolutions — implying 1,577,917,500 civil days per yuga and a sidereal day of 86,164.10 seconds (23h 56m 4.10s). The modern value is 86,164.09 seconds: agreement to about 0.01 s. The verse also encodes the rotating-Earth doctrine numerically ("of the Earth eastward") — the parameter later tradition recast as revolutions of the stars.

The Aryabhatiya of Aryabhata · tr. W. E. Clark, 1930

Aryabhatiya Golapada IV.37 (499 CE) gives the correct geometric mechanism of both eclipses: the Sun is obscured when the Moon comes between Earth and Sun; the Moon is obscured when it passes into the Earth's shadow. Brahmagupta directly attacked this in Brahmasphuta- siddhanta XI.9 (628 CE), calling Aryabhata's eclipse account "false" and re-affirming the demon Rahu. The geometric reading did not become Indian astronomical mainstream until the Kerala school ~1500 CE.

The Aryabhatiya of Aryabhata · tr. W. E. Clark, 1930

Aryabhatiya I.3 gives the cosmic-cycle structure: 14 Manus × 72 yugas × 4,320,000 years = 4,354,560,000 years per kalpa (~4.35 billion). Modern radiometric Earth age (Patterson 1956): 4.54 billion. ~5% match between a 6th-century Sanskrit recurrence period and 20th-century radioactive-decay measurement. Almost certainly coincidence — Aryabhata was computing planetary cycles, not Earth's age — but striking.

The Aryabhatiya of Aryabhata · tr. W. E. Clark, 1930

Aryabhatiya Golapada IV.9 uses the boat analogy to argue that the apparent westward motion of stars is an illusion caused by Earth's eastward axial rotation. Aryabhatiya I.1 quantifies it: 1,582,237,500 rotations per yuga ≈ 366.26 sidereal rotations per year, accurate to ~4 parts per million against modern measurement. Predates Copernicus by 1,044 years; contested within Indian astronomy itself (Brahmagupta rejected it in 628 CE).

The Aryabhatiya of Aryabhata · tr. W. E. Clark, 1930

Pañcasiddhāntikā III.21 (505 CE) states that the summer solstice once turned from the middle of Āśleṣā — "then the ayana was right" — but at present begins from Punarvasu: a shift of about 23°, roughly 1,700 years of equinoctial precession separating the old record from current observation. Hipparchus discovered precession c. 130 BCE; this verse documents the Indian tradition registering the same drift by checking its inherited solstice positions against the sky.

The Panchasiddhantika: The Astronomical Work of Varaha Mihira · tr. G. Thibaut & Sudhakara Dvivedi, 1889