month, in chronology, the conventional period of a lunation, i.e., passage of the moon through all its phases. It is usually computed at approximately 29 or 30 days. For the computation of the month and its harmony with the solar calendar and for the months in others than the Gregorian calendar, see calendar. For the difference between the sidereal month and the synodic month, see moon. Certain stones have in ancient and modern times been connected with the months; these lucky stones, or birthstones, are often given as follows: January [from the god Janus]: garnet; February [Lat., = expiatory, because of ancient rites]: amethyst; March [from the god Mars]: bloodstone or aquamarine; April: diamond; May: agate or emerald; June [from the gens Junius ]: pearl or moonstone; July [from Julius Caesar]: ruby or onyx; August [from Augustus]: carnelian or peridot; September [Lat., = seven; formerly the 7th month]: chrysolite or sapphire; October [eight]: beryl, tourmaline or opal; November [nine]: topaz; December [ten]: turquoise or zircon.
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