Eclipses occur in patterns. The Saros Series is a period of 223 lunar months that has been used to predict eclipses for thousands of years. In a Saros Series, exactly 9 years, 5.5 days after any lunar eclipse, a solar eclipse will occur, and vice versa. Approximately 6585.3211 days, or 18 years, 11 days, and 8 hours after one eclipse, the Sun, Earth, and Moon return to about the same relative geometry, and a nearly identical eclipse occurs. These similar eclipses are part of the same Saros Cycle, and the time between the two eclipses is called a saros.