The smallest unit of time is a nimesha; this is the amount of time it takes to blink. Fifteen nimeshas make one kashtha and thirty kashthas are one kala. Thirty kalas one muhurta and there are thirty muhurtas in one divaratra (one day). Fifteen muhurtas constitute the day and fifteen muhurtas make up the night. One month for humans is one day for the ancestors (pitri). Shuklapaksha is the lunar fortnight during which the moon waxes and krishnapaksha is the lunar fortnight during which the moon wanes. Shuklapaksha corresponds to night for the ancestors and krishnapaksha corresponds to day. Thus, thirty human months are merely one month for the ancestors. Three hundred and sixty human months are one year for the ancesotrs. One human year is one divaratara for the gods. The human year is divided into two ayanas, each consisting of six months. These are known as uttarayana and dakshinayana. Uttarayana is day for the gods and dakshinayana is night. Thirty human years are one month for the gods and three hundred and sixty human years are one year for the gods.
Time is divided into four yugas (eras). These are known as satya yuga or krita yuga, treta yuga, dvapara yuga and kali yuga. The lengths of these yugas are defined in terms of years of the gods. Satya yuga has four thousand years of the gods, treta yuga three thousand, dvapara yuga two thousand and kali yuga one thousand. A cycle of satya yuga, treta yuga, dvapara yuga and kali yuga is known as a mahayuga. Thus, a mahayuga would seem to consist of ten thousand years of the gods. But this is not quite correct. In between any two yugas are intervening periods, known as sandhyamshas. For example, the sandhyamsha for satya yuga is four hundred years, for teta yuga three hundred years, for dvapara yuga two hundred years and for kali yuga one hundred years. Once one adds the sandhyamshas, a mahayuga adds up to twelve thousand years of the gods. A little over seventy-one yugas constitute one manvantara. Fourteen such manvantaras are one kalpa. A kalpa is merely one day for Brahma. At the end of Brahma‘s day, the universe is destroyed. It is then created afresh when a new day dawns for Brahma.