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Nodal precession
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<p>Nodal precession is the <a href="/facts/Precession/44Sk1PMD">precession</a> of the <a href="/facts/Orbital_plane_(astronomy)/xPdMmVKP">orbital plane</a> of a <a href="/facts/Satellite/PTX8c68t">satellite</a> around the <a href="/facts/Rotation/yChkz49x">rotational</a> axis of an <a href="/facts/Astronomical_object/BCHLa0Q2">astronomical body</a> such as <a href="/facts/Earth/HLLmDfj0">Earth</a>. This precession is due to the non-spherical nature of a rotating body, which creates a non-uniform <a href="/facts/Gravitational_field/K1uTmJFy">gravitational field</a>. The following discussion relates to <a href="/facts/Low_Earth_orbit/rq1TwayJ">low Earth orbit</a> of artificial satellites, which have no measurable effect on the motion of Earth. The nodal precession of more massive, <a href="/facts/Natural_satellite/AE4KQKbq">natural satellites</a> like the <a href="/facts/Moon/zKHqEMPb">Moon</a> is more complex. </p><p>Around a spherical body, an orbital plane would remain fixed in space around the gravitational <a href="/facts/Primary_(astronomy)/PzvXx42a">primary body</a>. However, most bodies rotate, which causes an <a href="/facts/Equatorial_bulge/8CIPWl0I">equatorial bulge</a>. This bulge creates a gravitational effect that causes orbits to precess around the rotational axis of the primary body. </p><p>The direction of precession is opposite the direction of revolution. For a typical prograde orbit around Earth (that is, in the direction of primary body's rotation), the <a href="/facts/Longitude_of_the_ascending_node/926pTlve">longitude of the ascending node</a> decreases, that is the node precesses westward. If the orbit is <a href="/facts/Retrograde_and_prograde_motion/1HCbwQqy">retrograde</a>, this increases the <a href="/facts/Ecliptic_coordinate_system/28zkWwVa">longitude</a> of the <a href="/facts/Orbital_node/E5tUmCsY">ascending node</a>, that is the node precesses eastward. This nodal precession enables <a href="/facts/Sun-synchronous_orbit/3HonupUd">heliosynchronous orbits</a> to maintain a nearly constant <a href="/facts/Beta_angle/I5JXV3sC">angle relative to the Sun</a>. </p>