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The orbit of the Moon is a nearly circular ellipse about the Earth (the semimajor and semiminor axes are 384,400 km and 383,800 km, respectively: a difference of only 0.16%). The equation of the ellipse yields an eccentricity of 0.0549 and perigee and apogee distances of 362,600 km (225,300 mi) and 405,400 km (251,900 mi) respectively (a ...
The Moon is Earth 's only natural satellite. It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have over time synchronized the Moon's orbital period ( lunar month) with its rotation period ( lunar day) at 29.5 Earth days, causing the same side of the Moon ...
The far side of the Moon is the lunar hemisphere that always faces away from Earth, opposite to the near side, because of synchronous rotation in the Moon's orbit. Compared to the near side, the far side's terrain is rugged, with a multitude of impact craters and relatively few flat and dark lunar maria ("seas"), giving it an appearance closer ...
Newton applied his theorem to understanding the overall rotation of orbits (apsidal precession, Figure 3) that is observed for the Moon and planets. The term "radial motion" signifies the motion towards or away from the center of force, whereas the angular motion is perpendicular to the radial motion.
Earth's rotation axis moves with respect to the fixed stars (inertial space); the components of this motion are precession and nutation. It also moves with respect to Earth's crust; this is called polar motion. Precession is a rotation of Earth's rotation axis, caused primarily by external torques from the gravity of the Sun, Moon and other bodies.
Lunar precession. Lunar standstill: every 18.6 years, the declination range of the Moon reaches a maximum or minimum. Lunar precession is a term used for three different precession motions related to the Moon. First, it can refer to change in orientation of the lunar rotational axis with respect to a reference plane, following the normal rules ...
In astronomy, the rotation periodor spin period[1]of a celestial object(e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the sidereal rotation period(or sidereal day), i.e., the time that the object takes to complete a full rotationaround its axisrelative to the background stars (inertial space).
Apsidal precession is considered positive when the orbit's axis rotates in the same direction as the orbital motion. An apsidal period is the time interval required for an orbit to precess through 360°, [2] which takes the Earth about 112,000 years and the Moon about 8.85 years. [3]