Yuga in Hindu philosophy is the name of an epoch or era within a four age cycle. According to Hindu cosmology, life in the universe is created and destroyed once every 4.1 to 8.2 billion years, which is one full day and night for Brahma. The lifetime of Brahma himself believed to be 311 trillion and 40 billion years as per Hindu cosmology. The cycles are said to repeat like the seasons, waxing and waning within a greater time-cycle of the creation and destruction of our universe. Like Summer, Spring, Winter and Autumn, each yuga involves stages or gradual changes which the earth and the consciousness of mankind goes through as a whole. A complete Yuga cycle from a high Golden Age, called the Satya Yuga to a Dark Age, Kali Yuga and back again is said to be caused by the solar system's motion around another star.
Example via www.ramdass.org: Helping Out