polar motion

polar motion

a periodic rotation of the Earth's spin axis about a mean axis, somewhat like the wobble of a spinning top. Slight variations in latitude and longitude result from this wobble because the poles are displaced from their mean positions. The north pole of rotation rotates counterclockwise around its mean position.

Polar motion is primarily made up of two discrete periodic oscillations: one, called the Chandler Wobble, has about a 14-month period, and the other has a 12-month period. The combination of these two wobbles causes the poles to trace spiral paths out of, around, and eventually back into their mean positions over a period of about 6.5 years. The separation between the actual and mean poles was exceptionally large in about 1952, when they were separated by 12 m (37 feet), or 0.37 arc second (0.37″). Their maximum separation during the 6.5-year period averages about 0.25″.

Polar motion was first predicted by the Swiss physicist Leonhard Euler (Euler, Leonhard) in 1765 using dynamical theory and a rigid model of the Earth; he predicted a 10-month oscillation period for the phenomenon. Observational proof for the postulated latitude variations was obtained in the mid-1880s, and about that time the American astronomer S.C. Chandler (Chandler, Seth Carlo) analyzed these data and obtained both the 14-month and the 12-month periods. The four-month difference between Euler's predicted period and the actual duration of the Chandler Wobble is due to the elasticity of the Earth's mantle and the mobility of the oceans, which together subtly affect the Earth's response to rotation and for which Euler had not provided in his calculations.

Astronomical observations of the Earth's rotational position in space, which are used in determining Universal Time, must be corrected for slight variations in longitude caused by polar motion.

* * *

Universalium. 2010.

Look at other dictionaries:

• Polar motion — is the movement of Earth s rotation axis across its surface. 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 only a few… …   Wikipedia

• International Polar Motion Service — Der International Polar Motion Service (IPMS) ist der Nachfolger des Internationalen Breitendienstes. Er diente seit den 1970er Jahren zur genauen Überwachung der Erdrotation und ihrer Polbewegung und wurde in den 1980ern mit den Zeitdiensten zum …   Deutsch Wikipedia

• Polar Bear Expedition — Polar Bear Monument in White Chapel Cemetery, Troy, Michigan, sculptor Leon Hermant …   Wikipedia

• Polar Electro — Oy, or shortly Polar is pioneered and leading manufacturer of personal heart rate monitor registering and evaluation equipment. The company is based in Kempele, Finland. Founded in 1977 by University of Oulu professor Seppo Säynäjäkangas, who… …   Wikipedia

• Motion capture — Motion capture, motion tracking, or mocap are terms used to describe the process of recording movement and translating that movement on to a digital model. It is used in military, entertainment, sports, and medical applications, and for… …   Wikipedia

• Polar wander — is the phenomenon in which the North and South Poles of the Earth move with respect to the continents. This motion can be divided into two components, that due to continental drift (in which the continents move over the mantle), and true polar… …   Wikipedia

• Polar coordinate system — Points in the polar coordinate system with pole O and polar axis L. In green, the point with radial coordinate 3 and angular coordinate 60 …   Wikipedia

• Polar Express — Filmdaten Deutscher Titel: Der Polarexpress Originaltitel: The Polar Express Produktionsland: USA Erscheinungsjahr: 2004 Länge: 96 Minuten Originalsprache: Englisch …   Deutsch Wikipedia

• Movimiento polar — Diagrama mostrando el desplazamiento polar. El eje vertical corresponde al tiempo (unidades en días) y los ejes horizontales al desplazamiento sobre la superficie (cada segmento equivale a unos 3 metros sobre la superficie). Datos suministrados… …   Wikipedia Español

• Mechanics of planar particle motion — Classical mechanics Newton s Second Law History of classical mechanics  …   Wikipedia