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Related to Sideric month: Sidereal zodiac
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 calendarcalendar
[Lat., from Kalends], system of reckoning time for the practical purpose of recording past events and calculating dates for future plans. The calendar is based on noting ordinary and easily observable natural events, the cycle of the sun through the seasons with equinox
..... Click the link for more information. . For the difference between the sidereal month and the synodic month, see moonmoon,
natural satellite of a planet (see satellite, natural) or dwarf planet, in particular, the single natural satellite of the earth. The Earth-Moon System
The moon is the earth's nearest neighbor in space.
..... Click the link for more information. . 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 JanusJanus
, in Roman religion, god of beginnings. He was one of the principal Roman gods, the custodian of the universe. The first hour of the day, the first day of the month, the first month of the year (which bears his name) were sacred to him.
..... Click the link for more information. ]: garnet; February [Lat.,=expiatory, because of ancient rites]: amethyst; March [from the god MarsMars,
in Roman religion and mythology, god of war. In early Roman times he was a god of agriculture, but in later religion (when he was identified with the Greek Ares) he was primarily associated with war.
..... Click the link for more information. ]: bloodstone or aquamarine; April: diamond; May: agate or emerald; June [from the gens Junius]: pearl or moonstone; July [from Julius CaesarCaesar, Julius
(Caius Julius Caesar), 100? B.C.–44 B.C., Roman statesman and general. Rise to Power
Although he was born into the Julian gens, one of the oldest patrician families in Rome, Caesar was always a member of the democratic or popular party.
..... Click the link for more information. ]: ruby or onyx; August [from AugustusAugustus
, 63 B.C.–A.D. 14, first Roman emperor, a grandson of the sister of Julius Caesar. Named at first Caius Octavius, he became on adoption by the Julian gens (44 B.C.) Caius Julius Caesar Octavianus (Octavian); Augustus was a title of honor granted (27 B.C.
..... Click the link for more information. ]: 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.
monthThe period of the Moon's revolution around the Earth with reference to some specified point in the sky (see table). The differences in the monthly periods result from the complicated motion of the moon.
an interval of time nearly equal to the period of revolution of the moon about the earth. Different types of months are distinguished (see Table 1 and Figure 1). These include (1) the synodic month, which is the period of the sequence of the lunar phases (it serves as the basis for lunar calendars);
|Table 1. Length of various types of months|
|Type of month||Mean solar days||Mean solar time|
|Synodic .....||29.530588||29 days||12 hr||44 min||3 sec|
|Sidereal .....||27.321661||27 days||7 hr||43 min||12 sec|
|Tropical .....||27.321582||27 days||7 hr||43 min||4 sec|
|Anomalistic .....||27.554550||27 days||13 hr||18 min||33 sec|
|Nodical .....||27.212220||27 days||5 hr||5 min||36 sec|
(2) the sidereal month, during which the moon performs a complete revolution about the earth and returns to its original position relative to the stars; (3) the tropical month, which is the period during which the moon returns to a given longitude; (4) the anomalistic month, which is the interval of time between successive passages of the moon through the perigee; and (5) the nodical month, which is the period of time between successive passages of the moon through the same node of its orbit (this concept is important for the theory of eclipses). In the Gregorian calendar, the year is divided into 12 months, each month containing from 28 to 31 days; this calendar does not agree with the lunar phases.