Unit of the cosmic cycle in Hindu cosmology. Each yuga is progressively shorter than the preceding one, corresponding to a decline in the moral and physical state of humanity. Four such yugas make up a mahayuga; 2,000 mahayugas make up the basic cosmic cycle, the kalpa. The first yuga was an age of perfection that lasted 1,728,000 years. The fourth and most degenerate yuga began in 3102 BC and will last 432,000 years. At the close of this yuga, the world will be destroyed, to be recreated after a period of quiescence as the cycle resumes.