sahasra-yuga-paryantam
ahar yad brahmaṇo viduḥ
rātriṁ yuga-sahasrāntāṁ
te ‘ho-rātra-vido janāḥ
“By human calculation, a thousand ages taken together form the duration of Brahmā’s one day. And such also is the duration of his night.” [Bhagavad-gītā As It Is, 8.17]
Lord Brahma is the first created being in the universe, and is also the first demigod.
A day of Brahma is called a kalpa. One kalpa is equal to 1000 yuga cycles. There are four yugas in one cycle. The four yugas are: Satya-yuga (which lasts 1,728,000 years), Tretā-yuga (which lasts 1,296,000 years), Dvāpara-yuga (which lasts 864,000 years), and Kali-yuga (the yuga that we are currently in, which lasts 432,000 years). His night comprises the same number of years. This calculation continues to roll on to form one year. One hundred such years, or 311,040,000,000,000 (311 trillion and 40 billion) earth years, equals his lifetime.
