Earth's axis of rotation
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Understanding Earth's Axis of Rotation
Variability in Earth's Rotation Rate and Axis Position
The Earth's rotation is not constant; both the rate of rotation and the position of the rotation axis vary over time. Changes in the rotation rate are directly proportional to changes in the length of a day (LOD)1. Variations in the position of the rotation axis are classified as either "polar motion" or "nutation." Polar motion describes the movement of the axis relative to the Earth's surface, while nutation refers to the movement of the axis relative to inertial space1. These variations are influenced by different excitation processes, with long-term processes causing mostly polar motion and nearly diurnal processes causing mostly nutation1.
Causes of Polar Motion and Nutation
Polar motion can arise from the redistribution of mass within the Earth, such as mantle density heterogeneities. This motion is influenced by the Earth's viscosity structure and mantle flow fields, which are consistent with tomographic anomalies and lithospheric plate motions2. The gravitational attraction of the Sun and Moon also causes nutational motion due to their nearly diurnal periods as seen from Earth1.
Interdisciplinary Study of Earth's Rotation
The study of Earth's rotation involves multiple disciplines, including astronomy, geodesy, and geophysics. Changes in angular velocity affect the length of the day, while variations in the rotation axis position are associated with polar motion and precession-nutation3. Each discipline contributes to the observation, understanding, and modeling of these phenomena, providing a comprehensive view of Earth's rotational dynamics3.
Observational Techniques and Historical Data
Modern observations of Earth's rotation have significantly improved due to advancements in space geodetic methods such as satellite laser ranging (SLR), very long baseline interferometry (VLBI), lunar laser ranging (LLR), and the global positioning system (GPS)7. These techniques have enhanced our understanding of variations in Earth's rotation over different time scales, from hours to geological epochs7.
Geophysical Implications of Rotation Variations
Irregularities in Earth's rotation, both in its rate and axis position, are caused by various geophysical processes. Short-period fluctuations are influenced by seasonal shifts in air masses and variable winds, while long-term fluctuations are affected by climatic changes and sea levels5. These variations provide valuable insights into geophysical phenomena and help in studying Earth's internal and external dynamics5.
Stability of Earth's Spin Axis
Recent studies using paleomagnetic data suggest that the Earth's spin axis has remained relatively stable over the last 130 million years, with deviations of no more than approximately 5 degrees10. This stability indicates that mantle mass heterogeneities have not changed rapidly enough to drive significant true polar wander (TPW)10.
Conclusion
The Earth's axis of rotation is subject to complex variations influenced by internal and external geophysical processes. Understanding these variations requires an interdisciplinary approach, combining insights from astronomy, geodesy, and geophysics. Modern observational techniques have greatly enhanced our ability to study these phenomena, providing a deeper understanding of Earth's rotational dynamics and their geophysical implications.
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The Earth’s Rotation
Earth's rotation, influenced by various processes, is influenced by the length of a day, the gravitational attraction of celestial objects, and the Earth's rotation rate.
Changes of the Earth's rotation axis owing to advection of mantle density heterogeneities
The Earth's rotation axis follows closely changes in the axis of maximum non-hydrostatic moment of inertia, with the current rate of polar motion explaining 40% of observed geodetically.
Highly CitedEarth rotation as an interdisciplinary topic shared by astronomers, geodesists and geophysicists
Earth rotation is an interdisciplinary topic shared by astronomers, geodesists, and geophysicists, with each discipline contributing to its observation, understanding, and modeling at different time scales.
How do we know that the Earth spins around its axis?
The Earth spins around its axis using the Foucault pendulum and sideways deflection of moving objects in a rotating system, as demonstrated by experiments with a carousel.
Astronomy-Geophysics. (Book Reviews: The Rotation of the Earth. A geophysical discussion)
This book explores irregularities in the Earth's rotation, revealing factors such as seasonal shifts, variable winds, and climate changes, as well as a secular increase in the length of day.
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