sextant: a measuring instrument for measuring the angular distance between celestial objects; resembles an octant
measuring instrument: instrument that shows the extent or amount or quantity or degree of something
vedic literature: (from the Sanskrit word for `knowledge') any of the most ancient sacred writings of Hinduism written in early Sanskrit; traditionally believed to comprise the Samhitas, the Brahmanas, the Aranyakas, and the Upanishads