The study of astrology accords primary importance to time. Not even two smallest fractions of time element can be said to be similar. Each of them is different. Every fraction of time energises the living beings in the earth in many ways. The existence of planets and their effects on life in earth depends upon time cycle. Time is the force behind the creation and destruction of every organism in the cosmos. Time is classified into 9 types namely Brahmam, Divyam, Pithryam, Prajāpathyam, Gauravam, Souram, Savanam, Chhandram and Arkham.
Day and night calculations, the holy periods of Shadhasheethi and Vishnupathi and Dakshiṇāyaṇa and Uttarāyaṇa period are reckoned with the help of Souramānam.
One lunar month contains thirty days from Prathipādam to Amāvāsya. The daily rotation of the stellar sphere makes one star day. A Savana Day is of 60 Ghatis duration from one sunrise to the next sunrise. Thus, 360 Savana days form a Savana year. 365.25 days make a solar year (Souravarsham). Kalpa is one year of Lord Brahma and is equal to our 4,32,00,00,000 years.
There are four Yugas, namely:
1. Krutha or Satya = 17, 28,000 human years
2. Thretha = 12,96,000 human years
3. Dwāparam = 8, 64,000 human years
4. Kali = 4,32,000 human years