The nodal period (or draconic period) of a satellite is the time interval between successive passages of the satellite through either of its orbital nodes,[1][2] typically the ascending node.
It is distinct from the sidereal period, which measures the period with respect to reference stars seemingly fixed onto a spherical background, since the location of a satellite's nodes precess over time.
[3] For example, the nodal period of the Moon is 27.2122 days[4] (one draconic month), while its sidereal period is 27.3217 days[5] (one sidereal month).
The oblate figure of the Earth has important effects of the orbits of near-Earth satellites.
[6] 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:[7] where