The Vedic concept of Kala (time) is interesting. Our concept of the solar month is based on the Sun’s movement through each sign. The Sun’s movement across the twelve signs represents a sidereal year, which is equivalent to one divine day. Three hundred and sixty of such days are therefore one divine year. Twelve thousand divine years constitute a period of four Yugas (a Chaturyuga). Seventy-one Chaturyuga is a Manvantara; and fourteen Manvantara is a Kalpa or a day of Brahma (one thousand Yugas).
Duration of the different eras:
Krita (Satya) Yuga, 4,800 divine years – 1,728,000 human years (4 times Kali Yuga)
Treta Yuga, 3,600 divine years – 1,296,000 human years (3 times the size of Kali Yuga)
Dwapara Yuga, 2,400 divine years – 864,000 human years (2 times the size of Kali Yuga)
Kali Yuga, 1,200 divine years – 432,000 human years