Source : Webster's Revised Unabridged Dictionary (1913)

   {Cycle of indiction}, a period of 15 years, employed in Roman
      and ecclesiastical chronology, not founded on any
      astronomical period, but having reference to certain
      judicial acts which took place at stated epochs under the
      Greek emperors.

   {Cycle of the moon}, or {Metonic cycle}, a period of 19
      years, after the lapse of which the new and full moon
      returns to the same day of the year; -- so called from
      Meton, who first proposed it.

   {Cycle of the sun}, {Solar cycle}, a period of 28 years, at
      the end of which time the days of the month return to the
      same days of the week. The dominical or Sunday letter
      follows the same order; hence the solar cycle is also
      called the {cycle of the Sunday letter}. In the Gregorian
      calendar the solar cycle is in general interrupted at the
      end of the century.