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  2. Astronomical nutation - Wikipedia

    en.wikipedia.org/wiki/Astronomical_nutation

    An example of precession and nutation is the variation over time of the orientation of the axis of rotation of the Earth. This is important because the most commonly used frame of reference for measurement of the positions of astronomical objects is the Earth's equator — the so-called equatorial coordinate system .

  3. Precession - Wikipedia

    en.wikipedia.org/wiki/Precession

    The precession of Earth's axis was later explained by Newtonian physics. Being an oblate spheroid , Earth has a non-spherical shape, bulging outward at the equator. The gravitational tidal forces of the Moon and Sun apply torque to the equator, attempting to pull the equatorial bulge into the plane of the ecliptic , but instead causing it to ...

  4. Nutation - Wikipedia

    en.wikipedia.org/wiki/Nutation

    A pure nutation is a movement of a rotational axis such that the first Euler angle is constant. [citation needed] Therefore it can be seen that the circular red arrow in the diagram indicates the combined effects of precession and nutation, while nutation in the absence of precession would only change the tilt from vertical (second Euler angle).

  5. Axial precession - Wikipedia

    en.wikipedia.org/wiki/Axial_precession

    Precessional movement of Earth. Earth rotates (white arrows) once a day around its rotational axis (red); this axis itself rotates slowly (white circle), completing a rotation in approximately 26,000 years [1] In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational ...

  6. Chandler wobble - Wikipedia

    en.wikipedia.org/wiki/Chandler_wobble

    It amounts to change of about 9 metres (30 ft) in the point at which the axis intersects the Earth's surface and has a period of 433 days. [2] [3] This wobble, which is an astronomical nutation, combines with another wobble with a period of six years, so that the total polar motion varies with a period of about 7 years.

  7. Polar motion - Wikipedia

    en.wikipedia.org/wiki/Polar_motion

    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 variation is a few meters on the surface of the Earth.

  8. Earth-centered inertial - Wikipedia

    en.wikipedia.org/wiki/Earth-centered_inertial

    The gravitational attraction of the Sun and Moon on the Earth's equatorial bulge cause the rotational axis of the Earth to precess in space similar to the action of a top. This is called precession. Nutation is the smaller amplitude shorter-period (< 18.6 years) wobble that is superposed on the precessional motion of the Celestial pole. It is ...

  9. Sidereal time - Wikipedia

    en.wikipedia.org/wiki/Sidereal_time

    such that θ is the Earth Rotation Angle, E PREC is the accumulated precession, and E 0 is equation of the origins, which represents accumulated precession and nutation. [15] The calculation of precession and nutation was described in Chapter 6 of Urban & Seidelmann.