Overview
Paksha (Sanskrit: पक्ष, romanised: pakṣa) refers to a fortnight period consisting of various lunar phases within a month of the Hindu lunar calendar. The term literally means "side" in Sanskrit, and denotes the periods between amavasya (new moon) and purnima (full moon), and vice versa.
A lunar month in the Hindu calendar comprises two pakshas, with each fortnight further subdivided into lunar days known as tithis. A paksha consists of fifteen such tithis, each corresponding to a 12-degree angular motion of the Moon relative to the Sun.
The fortnight extending from amavasya to purnima is termed Shukla Paksha (bright side), also known as Gaura Paksha, and corresponds to the period of the waxing moon. The succeeding fortnight, from purnima to amavasya, is called Krishna Paksha (dark side) or Vadhya Paksha, corresponding to the period of the waning moon. Amavasya itself corresponds to the period when the Moon is within 12 degrees of angular distance from the Sun before their conjunction.
Two regional traditions exist for marking the commencement of a lunar month. In the amanta tradition, a lunar month begins on the day following amavasya, while in the purnimanta system, it begins on the day following purnima. The amanta system is followed largely in South India, whereas the purnimanta system is prevalent in North India.