The
Chandler wobble is a small motion in the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's axis of
rotationEarth's rotation is the rotation of the solid Earth around its own axis. The Earth rotates towards the east. As viewed from the North Star Polaris, the Earth turns counter-clockwise.- Rotation period :...
relative to the Earth's surface, which was discovered by
AmericanThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
astronomerAn astronomer is a scientist who studies celestial bodies such as planets, stars, and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
Seth Carlo ChandlerSeth Carlo Chandler, Jr. was an American astronomer.He was born in Boston, Massachusetts. During his last year in high school he performed mathematical computations for Benjamin Peirce, of the Harvard College Observatory.After graduating, he became the assistant of Benjamin A. Gould...
in 1891. It amounts to 0.7 arcseconds (about 15 meters on the Earth's surface) and has a period of 433 days. This wobble combines with another wobble with a period of one year so that the total
polar motionPolar 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...
varies with a period of about 7 years.
The Chandler wobble is an example of the kind of motion that can occur for a spinning object that is not a sphere; this is called a
free nutation.
The
Chandler wobble is a small motion in the
EarthEarth is the third planet from the Sun. It is the fifth largest of the eight planets in the solar system, and the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density...
's axis of
rotationEarth's rotation is the rotation of the solid Earth around its own axis. The Earth rotates towards the east. As viewed from the North Star Polaris, the Earth turns counter-clockwise.- Rotation period :...
relative to the Earth's surface, which was discovered by
AmericanThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
astronomerAn astronomer is a scientist who studies celestial bodies such as planets, stars, and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
Seth Carlo ChandlerSeth Carlo Chandler, Jr. was an American astronomer.He was born in Boston, Massachusetts. During his last year in high school he performed mathematical computations for Benjamin Peirce, of the Harvard College Observatory.After graduating, he became the assistant of Benjamin A. Gould...
in 1891. It amounts to 0.7 arcseconds (about 15 meters on the Earth's surface) and has a period of 433 days. This wobble combines with another wobble with a period of one year so that the total
polar motionPolar 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...
varies with a period of about 7 years.
The Chandler wobble is an example of the kind of motion that can occur for a spinning object that is not a sphere; this is called a
free nutation. Somewhat confusingly, the direction of the
Earth's spin axis relative to the stars also varies with different periods, and these motions (caused by the tidal attraction of the Moon and Sun) are also called
nutationNutation is a slight irregular motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight...
s, except for the slowest, which is the
precession of the equinoxesIn astronomy, axial precession is a gravity-induced, slow and continuous change in the orientation of an astronomical body's rotational axis. In particular, it refers to the gradual shift in the orientation of Earth's axis of rotation, which, like a wobbling top, traces out a cone in a cycle of...
.
The existence of a free nutation of the Earth was predicted by
Leonhard EulerLeonhard Paul Euler was a pioneering Swiss mathematician and physicist who spent most of his life in Russia and Germany. His surname is in English ; the common English pronunciation is incorrect....
in 1755 as part of his studies of the dynamics of rotating bodies. Based on the known
flatteningThe flattening, ellipticity, or oblateness of an oblate spheroid is the "squashing" of the spheroid's pole, towards its equator.-First and second flattening:...
of the Earth he predicted that it would have a period of 355 days. Several astronomers searched for motions with this period, but none were found. Chandler's contribution was to look for motions at any possible period; once the Chandler wobble was observed, the difference between its period and the one predicted by Euler was explained (by
Simon NewcombSimon Newcomb was a Canadian-American astronomer and mathematician. Though he had little conventional schooling, he made important contributions to timekeeping as well as writing on economics and statistics and authoring a science fiction novel.-Early life:Simon Newcomb was born in the town of...
) as being caused by the non-rigidity of the Earth. The full explanation for the period also involves the fluid nature of the Earth's core and oceans: the wobble in fact produces a very small ocean
tideTides are the rises and falls of sea level caused by the combined effect of rotation of the Earth and the gravitation of the Moon and the Sun. The tides occur with a period of approximately 12 and a half hours and are influenced by the shape of the near-shore bottom.Most coastal areas experience...
with an amplitude of
c. 6
mm-Education:*Master of Management, a post-graduate business degree* Master of Music, a music degree-Computer technology:* MediaMonkey, a digital media player and media library application* mm tree, Andrew Morton's Linux kernel tree...
, the
pole tide; the only tide not caused by bodies outside the Earth. Despite the small amplitude, the gravitational effects of the pole tide is easily detected by the
superconducting gravimeterA gravimeter or gravitometer, is an instrument used in gravimetry for measuring the local gravitational field of the Earth. A gravimeter is a type of accelerometer, specialized for measuring the constant downward acceleration of gravity...
(see
e.g. Fig. 2.3 in Virtanen 2006).
To measure the wobble, the
International Latitude ObservatoriesThe International Latitude Observatories were a system of six observatories located near the parallel of 39° 08' north latitude. They were used to measure the variation in latitude that occurs as a result of the wobble of the Earth on its polar axis...
were established in 1899. (The wobble is also called the
variation of latitude). These provided data on the Chandler and annual wobble for most of the 20th century,
though they were eventually superseded by other methods of measurement. Monitoring of the
polar motionPolar 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...
is now done by the International Earth Rotation Service.
The wobble's amplitude has varied since its discovery, reaching its largest size in 1910 and fluctuating noticeably from one decade to another. While it has to be maintained by changes in the
mass distributionMass distribution is a term used in physics and mechanics and describes the spatial distribution of mass within a solid body. In principle, it is relevant also for gases or liquids, but on earth their mass distribution is almost homogeneous.-Astronomy:...
or
angular momentumAngular momentum is a quantity that is useful in describing the rotational state of a physical system. For a rigid body rotating around an axis of symmetry , the angular momentum can be expressed as the product of the body's moment of inertia and its angular velocity...
of the Earth's
outer coreThe interior structure of the Earth, similar to the other, is layered. These layers can be defined by either their chemical or their rheological properties. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a...
,
atmosphereAn atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low...
, oceans, or crust (from
earthquakeAn earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph...
s), for a long time the actual source was unclear, since no available motions seemed to be coherent with what was driving the wobble. On 18 July 2000, however, the
Jet Propulsion LaboratoryJet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is situated in the northern portion of Pasadena...
announced that "the principal cause of the Chandler wobble is fluctuating pressure on the bottom of the
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
, caused by
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
and
salinitySalinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
changes and
windWind is the flow of air or other gases that compose an atmosphere . On Earth, wind consists of the bulk movement of air...
-driven changes in the circulation of the oceans."
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