Nakshatra

Nakshatra (Sanskrit नक्षत्र, nakṣatra — "the unmoving", "stellar constellation") is a lunar mansion, one of 27 (sometimes 28) constellations in Vedic astrology, through which the Moon passes during a sidereal month (~27.3 days).

Size of a mansion. Each Nakshatra occupies 13°20′ of the ecliptic (360° / 27 = 13°20′).

The Oldest Layer of Indian Astronomy

Mentioned in the Rigveda. Nakshatras are the oldest layer of Indian astronomy, mentioned in the Rigveda (c. 1500 BCE). It is an older system than the zodiac.

Structure of Each Nakshatra

Each Nakshatra has:

• A ruling Graha (ग्रह) — determines the starting Dasha period
• A deity (Devata, देवता) — mythological archetype
• Shakti (शक्ति) — a special power or ability
• Gana (गण) — temperament: Deva (divine), Manushya (human), Rakshasa (demonic)

Grouping by Grahas

27 = 9 × 3. The 27 Nakshatras are grouped into 9 triples, each ruled by one of the Navagraha.

The Birth Nakshatra

Key to the Dasha. The position of the Moon in a Nakshatra at birth (Janma-Nakshatra, जन्मनक्षत्र) determines the sequence of Dasha periods (#18) and is considered one of the key indicators of a chart.

An extra layer in Sankhya Shastra. In Sankhya Shastra (#30), the Nakshatra system is used as an additional layer of interpretation of numerical destiny.