A paksha is the moon’s fortnight – lunar fortnight. Two pakshas make a month – Shukla Paksha and Krishna Paksha. The fortnight during which the moon is waxing is called Shukla or Shuddha or the bright phase of moon. This begins with the end of Amavasya (No moon day) and lasts up to the end of Pournami (Purnima or full moon day).
The fortnight during which the moon is waning is called
Krishna or Bahula. This lasts from the end of Poornima (full moon) to end of Amavasi (No moon).
Each chandramana maas or lunar month consists of both the pakshas (halves), Shukla paksha (Bright half) and Krishna Paksha (Dark half).
A month in the calendars followed in
North India begins with the Krishna Paksha – after the full moon or Purnima.
A month in traditional calendars followed in Gujarat,
Maharashtra, Andhra Pradesh and Karnataka begins with the Shukla Paksha – after Amavasi or no moon.