Rotation (green), Precession (blue) and Nutation (red) of the Earth

Nutation is a slight irregular motion (etymologically a "nodding") in the axis of rotation of a largely axially symmetric object, such as a gyroscope or a planet. Image File history File links From German Wikipedia, by User Herbye. ... Image File history File links From German Wikipedia, by User Herbye. ... The axis of rotation of a rotating body is a line such that the distance between any point on the line and any point of the body remains constant under the rotation. ... Acrobatic bicycle is possible thanks to gyroscopic effects A gyroscope is a device for measuring or maintaining orientation, based on the principle of conservation of angular momentum. ... Jump to: navigation, search A planet in common parlance is a large object in orbit around a star that is not a star itself. ...

The nutation of a planet is due to the fact that the tidal forces which cause precession of the equinoxes vary over time so that the speed of precession is not constant. It was discovered in 1728 by the English astronomer James Bradley, but was not explained until 20 years later. The tidal force is a secondary effect of the force of gravity and is responsible for the tides. ... There are two types of precession: torque-free precession and torque-induced precession. ... It has been suggested that Equinoctial point be merged into this article or section. ... Events Astronomical aberration discovered by the astronomer James Bradley Swedish academy of sciences founded at Uppsala Births January 9 - Thomas Warton, English poet (d. ... James Bradley (1693 – July 13, 1762) was an English astronomer, Astronomer Royal from 1742. ...

Because the dynamics of the planets are so well known, nutation can be calculated within seconds of arc over periods of many decades. There is another disturbance of the Earth's rotation called polar motion that can be estimated only a few months ahead, because it is influenced by rapidly and unpredictably varying things such as ocean currents, wind systems, and motions in the Earth's core. This article needs to be wikified. ...

Values of nutation are usually divided into components parallel and perpendicular to the ecliptic. The component which works along the ecliptic is known as the nutation in longitude. The component perpendicular to the ecliptic is known as the nutation in obliquity. Celestial coordinate systems are based on an "equator" and "equinox," which means a great circle in the sky that is the projection of the Earth's equator outwards, and a line, the Vernal equinox intersecting that circle, which determines the starting point for measurement of right ascension. These items are affected both by precession of the equinoxes and nutation, and thus depend on the theories applied to precession and nutation, and on the date used as a reference date for the coordinate system. In simpler terms, nutation (and precession) values are important in observation from Earth for calculating the apparent positions of astronomical objects. The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... Illumination of Earth by Sun on the day of equinox In astronomy, the vernal equinox (spring equinox, March equinox, or northward equinox) is the moment when the sun appears to cross the celestial equator, heading northward. ... Right ascension (RA; symbol α: Greek letter alpha) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. ... There are two types of precession: torque-free precession and torque-induced precession. ... Jump to: navigation, search Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. ...

Nutation of Earth

In the case of Earth, the principal sources of tidal force are the Sun and Moon, which continually change location relative to each other and thus cause nutation in Earth's axis. The largest component of Earth's nutation has a period of 18.6 years, the same as that of the precession of the Moon's orbital nodes. However, there are other significant periodical terms which must be calculated depending on the desired accuracy of the result. A mathematical description (set of equations) that represents nutation is called a "theory of nutation" (see,e.g. [1]). Generally, the theory is really a theory, in the sense that it applies physical laws and astronomical measurements; however, there may be parameters which are adjusted in a more or less ad hoc way to obtain the best fit to data. As can be seen from the IERS publication just cited, nowadays simple rigid-body mechanics do not give the best theory; one has to account for deformations of the solid Earth. Jump to: navigation, search Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. ... The Sun is the star at the centre of our Solar system. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... A node is one of two points where a bodys orbit crosses the ecliptic, called the ascending node (when the body is moving northward) and descending node (when the body is moving southward). ... The International Earth Rotation Service (IERS) is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Paramater (EOP) and International Celestial Reference System (ICRS) groups. ...