<P> The properties of the orbit described in this section are approximations . The Moon's orbit around Earth has many irregularities (perturbations), the study of which (lunar theory) has a long history . </P> <P> The orbit of the Moon is distinctly elliptical, with an average eccentricity of 0.0549 . The non-circular form of the lunar orbit causes variations in the Moon's angular speed and apparent size as it moves towards and away from an observer on Earth . The mean angular movement relative to an imaginary observer at the Earth - Moon barycentre is 7001131760000000000 ♠ 13.176 ° per day to the east (Julian day 2000). </P> <P> The Moon's elongation is its angular distance east of the Sun at any time . At new moon, it is zero and the Moon is said to be in conjunction . At full moon, the elongation is 180 ° and it is said to be in opposition . In both cases, the Moon is in syzygy, that is, the Sun, Moon and Earth are nearly aligned . When elongation is either 90 ° or 270 °, the Moon is said to be in quadrature . </P> <P> The orientation of the orbit is not fixed in space, but rotates over time . This orbital precession is also called apsidal precession and is the rotation of the Moon's orbit within the orbital plane, i.e. the axes of the ellipse change direction . The Moon's major axis--the longest diameter of the orbit, joining its nearest and farthest points, the perigee and apogee, respectively--makes one complete revolution every 8.85 Earth years, or 3,232.6054 days, as it rotates slowly in the same direction as the Moon itself (direct motion). The Moon's apsidal precession is distinct from the nodal precession of its orbital plane and axial precession of moon itself . </P>

Information about the path of revolution of moon around the earth