Spin, Wobble, and Nutation

Abstract

Observing and Understanding Earth Rotation: A Joint GGOS/IAU Science Workshop; Shanghai, China, 25–28 October 2010; The Earth rotates about its axis once a day, but it does not do so uniformly. Instead, the rate of rotation fluctuates by as much as a millisecond a day, the Earth wobbles as it rotates because the Earth's mass is not balanced about its rotation axis, and the Earth's rotation axis precesses and nutates in space. These variations in the Earth's rotation are caused by processes acting within the interior of the Earth such as glacial isostatic adjustment and core‐mantle interaction torques, by processes acting at the surface of the Earth such as fluctuations in the transport of mass within the atmosphere and oceans, and by processes acting external to the Earth such as torques due to the gravitational attraction of the Sun, the Moon, and the planets. These and other aspects of the Earth's rotation were discussed at a recent workshop in China that attracted 90 participants from 12 countries. The workshop was jointly organized by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy and Commission 19 (Rotation of the Earth) of the International Astronomical Union (IAU). The objectives of the workshop were to (1) assess our ability to observe the Earth's time‐varying rotation, (2) assess our understanding of the causes of the observed variations, (3) assess the consistency of Earth rotation observations with global gravity and shape observations, and (4) explore methods of combining rotation, gravity, and shape observations to gain greater understanding of the processes causing them to change on both the Earth and other planets, like Mars.