Lalla

Lalla was an early Indian astronomer.

He wrote the. It contains an extensive discussion of matters regarding the Celestial Sphere. He discusses how it appears to the residents of the South Pole (demons) and the residents of the North Pole (gods), what would happen if they walked towards the equator, and how they see the sun. He discusses calculations of the latitudes. He also mentioned many of the ideas of the Purāṇas that contemporary astronomers did not agree with, such as the earth being flat, infinite, riding on an animal, having two suns and moons, the sun being in front of the moon, the earth floating on water, riding on a tortoise, the eclipses being a monster Rāhu, etc etc. He goes on to make several logical arguments against these notions, using counter-examples &c.

He also disupted notions of eclipses, using the concept of parallax. One was that Rāhu was the cause of eclipses. Rāhu he describes as the decapitated head of a demon who had been 'drinking the nectar' when Hari chopped it off. Due to a boon of Brahmā, his decapitated, floating head shows up on new-moon and full-moon days and eats the sun. Or the moon. Depending. Lalla also describes the theory of a snake eating the sun and moon.

He also criticizes the theory of a 'moving earth', including Āryabhaṭa's rotating earth theory. He makes several arguments against both theories. Of the latter, he asks why arrows shot up do not fall to the west, and why clouds move the way they do.

Armillary sphere
Each of the 7 planets gets a set of the following:


 * epicycle
 * eccentric
 * dṛṅmaṇḍala
 * dṛkkṣepamaṇḍala
 * apamaṇḍala / kakṣāmaṇḍala

Each of the 5 star-planets gets:


 * śīghra epicycle
 * śīghra eccentrics
 * vimaṇḍala

The moon also gets a vimaṇḍala

12 instruments of astronomy
In, Lalla describes his "twelve instruments of astronomy". They were:


 * Gola-yantra (sphere)
 * Bhagaṇa-yantra
 * Cakra-yantra (circle)
 * Dhanu-yantra (half circle)
 * Ghaṭī-yantra (water instrument to measure time)
 * Śaṅku-yantra
 * Śakaṭa-yantra
 * Kartarī-yantra
 * Pīṭha-yantra
 * Kapāla-yantra
 * Śalākā-yantra
 * Yaṣṭi-yantra

He also listed 'accessories' needed to use the instruments:


 * karṇa (hypotenuse)
 * shadow (presumably of a gnomon)
 * day semi-duration
 * Sun's longitude
 * place's latitude
 * plumb
 * compass
 * water
 * intelligence
 * effort