LUNAR CYCLE. — In chronology, this term (Latin *circulus lunae* or *lunaris*; French *cycle lunaire*; German *Mondszythus*) designates a period of nineteen solar years, equivalent to 235 lunations or lunar months, necessary for a given moment in the solar year to coincide again with the same lunar phase.
It is one of the computations used in the Middle Ages for determining Easter: already employed by the Greeks, the Jews derived it from them in 338 AD. In itself, it corresponds exactly to the so-called "nineteen-year cycle" (*circulus decennovennalis*), with which it is often confused, but it differs in the ideal starting date, which in the lunar cycle is calculated to 3 AD, whereas in the nineteen-year cycle it is placed in the year 1 BC. It is found cited in some medieval documents alongside the date.