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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.
Epicyclical motion is used in the Antikythera mechanism, [citation requested] an ancient Greek astronomical device, for compensating for the elliptical orbit of the Moon, moving faster at perigee and slower at apogee than circular orbits would, using four gears, two of them engaged in an eccentric way that quite closely approximates Kepler's ...
The accuracy of this calculation requires that the two dates chosen be along the elliptical orbit's minor axis and that the midpoints of each half be along the major axis. As the two dates chosen here are equinoxes, this will be correct when perihelion, the date the Earth is closest to the Sun, falls on a solstice. The current perihelion, near ...
Polar motion in arc-seconds as function of time in days (0.1 arcsec ≈ 3 meters). [1] Polar motion of the Earth is the motion of the Earth's rotational axis relative to its crust. [2]: 1 This is measured with respect to a reference frame in which the solid Earth is fixed (a so-called Earth-centered, Earth-fixed or ECEF reference frame). This ...
When the curvature of the Earth is taken into account, the independence of the two motion does not hold. For example, even a projectile fired in a horizontal direction (i.e., with a zero vertical component) may leave the surface of the spherical Earth and indeed escape altogether.
Copernicus' displacement of the Earth from the center of the cosmos obviated the primary need for Ptolemy's epicycles: It explained retrograde movement as an effect of perspective, due to the relative motion of the earth and the planets. However, it did not explain non-uniform motion of the Sun and Moon, whose relative motions Copernicus did ...
The Chandler wobble or Chandler variation of latitude is a small deviation in the Earth's axis of rotation relative to the solid earth, [1] which was discovered by and named after American astronomer Seth Carlo Chandler in 1891. It amounts to change of about 9 metres (30 ft) in the point at which the axis intersects the Earth's surface and has ...
The stars viewed from Earth are seen to proceed from east to west daily (at about 15 degrees per hour), due to the Earth's diurnal motion, and yearly (at about 1 degree per day), due to the Earth's revolution around the Sun. At the same time the stars can be observed to anticipate slightly such motion, at the rate of approximately 50 arc ...