Nodal period
The nodal period of a satellite is the time interval between successive passages of the satellite through either of its orbital nodes, typically the ascending node. This applies to artificial satellites like weather satellites, and natural satellites like the Moon. The nodal period of the Moon is 27.2122 days.
The oblate figure of the Earth has important effects of the orbits of near-Earth satellites. An expression for the nodal period (Tn) of a near circular orbit, such that the eccentricity (ε) is almost but not equal to zero, is the following:
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