This succession of pole stars is a result of Earth's precessional motion.
2.
Nutation is the smaller amplitude shorter-period ( < 18.6 years ) wobble that is superposed on the precessional motion of the Celestial pole.
3.
A precessional motion of the orbit plane is caused by the oblatedness of the Earth ( J _ 2 ), and the gravitational effects of Sun and Moon.
4.
The attitude of the spacecraft about its center of gravity was controlled to scan the celestial sphere in a regular precessional motion maintaining a constant inclination between the spin axis and the direction to the Sun.
5.
The Earth, in addition to its diurnal ( daily ) rotation upon its axis and annual rotation around the Sun, incurs a precessional motion involving a slow periodic shift of the axis itself : approximately one degree every 72 years.
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