Techniques of determining latitude in Indian astronomical treatises

Abstract

The latitude-longitude coordinate system is a well-known method of expressing one’s location on the earth’s surface. It can be ascertained from references in Indian astronomical treatises that the idea of latitude was well established in this tradition for a long time. It was important for several problems in astronomy, especially for one’s location, and was measured using specific techniques and instruments. This paper brings together some of the chief techniques provided in these texts and classifies them. It is found that the primary method is finding the equinoctial midday shadow using a gnomon and working out the zenith distance from there. Other methods include finding the shadow on any given day with the gnomon and back-computing the latitude, and measuring the polar altitude. In this context, the instruments for this purpose have also been discussed.