Cycle

Cycle (Gr., 'a circle'), in Astronomy and Mathematical Chronology, a period or interval of time in which certain phenomena always recur in the same order. There are two great natural cycles, that of the sun and that of the moon. The solar cycle is a period of twenty-eight Julian years, after which the same days of the week recur on the same days of the year. The lunar or Metonic cycle consists of nineteen years or 235 lunations (see CHRONOLOGY), after which the successive new moons happen on the same days of the year as during the previous cycle. The number of the year in the cycle of the moon is called the Golden Number (q.v.). The cycle of Indictions (q.v.) is purely arbitrary, its years being fifteen, a conventional number; and the Julian Period, which combines and harmonises all the three others, might be termed the cycle of cycles. The term 'cycle of eclipses' is an instance of the more general use of the word, meaning the period of 223 lunations, within which seventy eclipses recur in the same order and magnitude—viz. twenty-nine of the moon and forty-one of the sun.