Kali Yuga (Devanāgarī: कलियुग [kəli juɡə], lit. "age of [the demon] Kali", or "age of vice") is the last of the four stages the world goes through as part of the cycle of yugas described in the Sanskrit scriptures, within the present Mahayuga. The other ages are called Satya Yuga, Treta Yuga, and Dvapara Yuga.
There is considerable controversy over the date for the start of the Kali Yuga and its duration. According to the Surya Siddhanta, Kali Yuga began at midnight (00:00) on 18 February 3102 BCE. This is also considered the date on which Lord Krishna left the earth to return to his heavenly abode. This information is placed at the temple of Bhalka, the place of this incident (see photo).
According to the astronomer and mathematician Aryabhatta the Kali Yuga started in 3102 BCE. He finished his book “Aryabhattiya” in 499 CE, in which he gives the exact year of the beginning of Kali Yuga. He writes that he wrote the book in the "year 3600 of the Kali Age" at the age of 23. As it was the 3600th year of the Kali Age when he was 23 years old, and given that Aryabhatta was born in 476 CE, the beginning of the Kali Yuga would come to (3600 - (476 + 23) + 1 (As only one year elapses between 1 BCE and 1 CE) = ) 3102 BCE.