A system of 27 asterisms, or nakṣatras, plays an important role in Indian astronomy and calendrical science. The present convention is that the ecliptic is divided into 27 equal parts each 13°20' long commencing from one initial point. These arcs are called nakṣatras. Again a bright or prominent star of each division is called yogatārā bearing the name of the are division e.g., Kṛttikā as nakṣatra means an are division and as a yogatārā it means the star η Tauri of the Pleiades group.

The origin of this asterism system is very old. The names of these stars appearin Vedic litrature. The Taittirīya, Kāṭhaka, Maitrāyaṇī Saṃhitas and the 19th book of Atharva Veda, each has given a list of 27 nakṣatras (the last two have included an additional star, Abhijit (αLyrae), making a total of 28 nakṣatras). All these lists always begin with the name kṛttikas (the star group Pleiades), and order of names of stars are more or less the same. Some of the stars changed their names in different hands; but they are always either star groups or single stars, and never arc divisions.