CHAPTER III DIRECTION, PLACE AND TIME. JUNCTION-STARS OF THE ZODIACAL ASTERISMS AND CONJUNCTION OF PLANETS WITH THEM them. (1) DIRECTION, PLACE AND TIME. Setting up of the gnomon : 1. After having tested the level of the ground by means of water, draw a neat circle with a pair of compasses. (At the centre of that circle, set up a vertical gnomon). The gnomon should be large, cylindrical, massive, and tested for its perpendicularity by means of four threads with plumbs tied to Bhaskara I in his commentary on the Aryabhatiya¹ tells us that there was difference of opinion amongst astronomers in his time regarding the shape and size of a gnomon (also called style). Some astronomers prescribed a gnomon with its one third in the bottom of the shape of a prism on a square base (caturaśra), one-third in the middle of the shape of a cow's tail (gopucchakāra), and one-third at the top of the shape of a spear-head (śülākāra); and some others prescribed a square prismoidal (samacaturaśra) gnomon. The followers of Aryabhata I, he informs us, prescribed the use of a broad (prthu), massive (guru), and large (dirgha) cylindrical gnomon, made of excellent timber, and free from any hole, scar, or knot on its body. In the above stanza Bhaskara I prescribes this last kind of gnomon: the other two kinds he proves in the commentary to be defective and so he rejects them. For getting the shadow-end easily and correctly, the cylindrical gnomon was surmounted by a fine cylindrical iron or wooden nail fixed vertically at the centre of the upper end. The nail was taken to be longer than the radius of the gnomon, so that its shadow was always seen on the ground. 2 ¹ ii. 14. 2 See Bhaskara I's commentary commentary on MBh, iii. 1.. Ā, ii. 13. Also see Parameśvara's
