The Nakshatra system is found in one of the most ancient and extant Indian texts on astronomy and astrology (Jyotisha) known as Vedāṅga Jyotiṣa, Jyotiṣavedāṅga  (Devanagari:  वेदाङ्ग ज्योतिष)  Jyotiṣavedāṅga  The current form of the text is dated to circa 700 BCE but it is based on a tradition reaching back to about 1400 BCE  The text is foundational to Jyotisha, one of the Vedanga disciplines. 

.There are 27 nakshatras divided again into 4 quarters called padas (legs/feet). The length of a nakshatra pada is 3º 20′ Later developments include various forms of Lunar Mansions employing 28 rather than 28 mansions

Rig Veda Vedanga Jyotisha di Lagadha