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18 year cycle of the moon4/14/2024 The period of the lunar nodal precession is defined as the time it takes the ascending node to move through 360° relative to the vernal equinox (autumnal equinox in Southern Hemisphere). The lunar nodes are the points where the Moon's orbit intersects the ecliptic.Īnother type of lunar orbit precession is that of the plane of the Moon's orbit. ![]() Nodal precession occurs every 18.6 years. ![]() This causes an eclipse season approximately every six months. Nodal precession Approximate axial parallelism of the Moon's orbit results in relative revolution of the lunar nodes as the Earth revolves around the Sun. This apsidal precession completes one rotation in the same time as the number of sidereal months exceeds the number of anomalistic months by exactly one, after about 3,233 days (8.85 years). This is the reason that an anomalistic month (the period the Moon moves from the perigee to the apogee and to the perigee again) is longer than the sidereal month (the period the Moon takes to complete one orbit with respect to the fixed stars). ![]() This kind of precession is that of the major axis of the Moon's elliptic orbit (the line of the apsides from perigee to apogee), which precesses eastward by 360° in approximately 8.85 years.
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