:In Egyptian mythology, Month is an alternate spelling for Menthu.
The month is a unit of time, used with calendars, which is approximately as long as some natural period related to the motion of the Moon (i.e. "Moonth"). The traditional concept arose with the cycle of moon phases; such months are synodic months and last ~29.53 days. From excavated tally sticks, researchers have deduced that people counted days in relation to the Moon's phases as early as the paleolithic age. Synodic months are still the basis of many calendars.
1 Astronomical Background
The motion of the Moon in its orbit is very complicated and its period is not constant. Moreover, many cultures (most notably those using the Hebrew (Jewish) and Islamic calendars) start a month with the first appearance of the thin crescent of the new moon after sunset over the western horizon. The date and time of this actual observation depends on the exact geographical longitude as well as latitude, atmospheric conditions, the visual acuity of the observers, etc. Therefore the beginning and lengths of months in these calendars can not be accurately predicted. Most Jews currently follow a precalculated calendar, but the Karaites rely on actual moon observations.
1.1 sidereal month
The actual period of the Moon's orbit as measured in a fixed frame of reference is known as a sidereal month (\si-dir'-e-ǝl, sǝ- \), because it is the time it takes the Moon to return to the same position on the celestial sphereIn astronomy and navigation, the celestial sphere is an imaginary rotating sphere of "gigantic radius", concentric with the Earth. All objects in the sky can be thought of as lying upon the sphere. Projected, from their corresponding terran equivalents, a among the fixed starFor alternate meanings see star (disambiguation Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. A star is any massive gaseous celestial body in outer space. Stars appear as shining points in the nighttime sky that twinkle becs (Latin: sidus): about 27 1/3 days on average. This type of "month" has appeared among cultures in the Middle East, India, and China in the following way: they divided the sky in 28 lunar station s, characterized by asterisms (groups of stars), one for each day that the Moon follows its track among the stars.
1.2 tropical month
It is customary to specify positions of celestial bodies with respect to the vernal equinoxIn astronomy, an equinox is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator. The word "equinox" comes from the Latin for equal night . The equinoxes in March and September are the two time. Because of precessionPrecession (also called gyroscopic precession is the phenomenon by which the axis of a spinning object (e. a part of a gyroscope) "wobbles" when a torque is applied to it. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can, this point moves back along the ecliptic. Therefore it takes the Moon less time to return to the equinox than to the same point amidst the fixed stars. This slightly shorter period is known as tropical month; cf. the analogous tropical yearA tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). The precise length of time depends on which point of the ecliptic one of the SunThe Sun (also called Sol is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally capt. This type of month is not used much.
