70
ARYABHATlYA
20. The east and west line and the north and south line and the perpendicular from zenith to nadir intersect in the place where the observer is.
21. The vertical circle which passes through the place where the observer is and the planet is the drnmandala. There is also the drkksepamandala which passes through the nonagesimal point.[1]
The nonagesimal or central-ecliptic point is the point on the ecliptic which is 90 degrees from the point of the ecliptic which is on the horizon.
These two circles are used in calculating the parallax in longitude in eclipses.
22. A light wooden sphere should be made, round, and of equal weight in every part. By ingenuity one should cause it to revolve so as to keep pace with the progress of time by means of quicksilver, oil, or water.[2]
Sukumar Ranjan Das[3] remarks that two instruments are named in this stanza (the gola and the cakra). I can see no reference to the cakra.
23. On the visible half of the sphere one should depict half of the sphere of the asterisms by means of sines. The equinoctial sine is the sine of latitude. The sine of colatitude is its koti.
The sine of the distance between the Sun and the zenith at midday of the equinoctial day is the equinoctial sine. This is the same as the equinoctial shadow and equals the sine of latitude. It is the base.
