The Moon's path around the Earth is divided into 27 equal parts called nakshatras, or lunar mansions. Each nakshatra is about 13 degrees and 20 minutes of the zodiac. The Moon spends roughly one day in each, which is why the birth nakshatra is so important in Vedic astrology.
Every nakshatra has a ruling deity, a symbol and a planetary ruler. For example, Ashwini is ruled by the Ashwini twins and symbolised by a horse's head; it brings speed, healing and initiative. Bharani is ruled by Yama and carries themes of bearing, discipline and transformation. Krittika, ruled by Agni the fire god, brings purification and sharpness.
The nakshatra of the Moon at birth is called the janma nakshatra. It influences the mind, emotional nature and the timing of life events through dasha periods. The nakshatra of the ascendant also colours the personality and life path.
Nakshatras add a deeper layer to the signs. Two people with the same Moon sign but different nakshatras can have very different temperaments. Learning the nakshatras turns a broad portrait into a finely detailed picture.