There are 27 नक्षत्र (Nakshatras), which means lunar mansions in Vedic astrology.
According to Hindu ancient scriptures, The Nakshatras are 27 daughters of Daksha Prajapati. All of them were married to Chandra, moon god.
Their names are as follows,
Ashwini
Bharani
Krittika
Rohini
Mrigashira
Ardra
Punarvasu
Pushya
Ashlesha
Magha
Purva
Phalguni
Uttara Phalguni
Hasta
Chitra
Swati
Vishakha
Anuradha
Mula
Purva Ashadha
Uttara Ashadha
Shravana
Dhanishtha,
Shatabhisha
Purva Bhadrapada
Uttara Bhadrapada
Revati
Daksha Prajapati cursed the Chandra:
The moon god, Chandra was married to all 27 sisters, but was deeply loved only with Rohini. He spent nearly all his time with her and neglected his other 26 wives. They complained to their father about Chandra’s behaviour. Daksha Prajapati requested him to treat all of his daughters equally. But Chandra kept ignoring them. Daksha Prajapati cursed him that Chandra will lose all his radiance. Chadra lost his glow, which created a cosmic effect on the universe. Lord Brahma advised him to perform intense penance to Lord Shiva. Chandra choose Triveni Sangam which is the confluence of three rivers; Kapila, Hiran, and Sarasvati for his penance. Lord Shiva appeared and partially revoked the curse. Chandra will lose his glow for 15 days and regain his glow for 15 days. When he looses his glow it is known as कृष्णपक्षः (Krishnapaksah) means waning and when he gain his glow it is known as शुक्लपक्षः (Shuklapaksah) means waxing. This means Chandra will travel and visit one of his wives while completing his orbit.
It is said that Chandra Chandra built the first temple at this place which is known as Somnath Temple, the first of the twelve Jyotirlinga in gratitude.