A lunar month in Hindu calendar has two fortnights – Shukla
Paksha and Krishna Paksha. Shukla is waxing or light phase of moon and Krishna is waning or dark phase of moon. Shukla Paksha starts
after Amavasi or no moon day. Krishna Paksha starts after Full moon or Purnima.
Shukla Paksha starts after new moon or Amavasya.
Each paksha has 15 tithis.
Each tithi has a name starting from
Amavasya
Pratipada
Dwitiya
Tritiya
Chaturthi
Panchami
Sashti
Saptami
Ashtami
Navami
Dasami
Ekadasi
Dwadasi
Trayodasi
Chaturdasi
Purnima
Earlier each tithi of the Krishna Paksha and Shukla Paksha
had separate names but now it has been discontinued. Krishna
or Shukla is prefixed to demarcate the tithis during each fortnight.
Krishna Paksha is mainly used for conducting ceremonies
dedicated to dead ancestors.