The Chandler Wobble

The Chandler Wobble is a small motion in the Earth's axis of rotation relative to the Earth's surface, discovered by American astronomer Seth Carlo Chandler, Jr., in 1891. It is one of several wobbling motions the Earth undergoes as it spins on its axis. Swiss mathematician Leonhard Euler theorized that the Earth wobbled as it rotated on its poles, resulting in a periodic variation in latitude at every point on Earth, but he could not prove the theory because the variations were too small for 18th century instruments to detect. In 1891, after German astronomer Karl Friedrich Kustner claimed to have detected variations in latitude at the Berlin Observatory, the International Geodetic Association launched an international observing program to confirm his results, organizing simultaneous observations in Germany and Hawaii on opposite sides of the globe. That same year, Seth Carlo Chandler confirmed the wobble using his own observations and those of others from observatories around the world, verifying annual motion caused by the seasonal relocation of Earth's mass each year and a second motion with a 14-month cycle. Both terms were very small, only one or two tenths of a second of arc, which explained why they had been so difficult to detect. The Chandler Wobble amounts to about 20 feet on the Earth's surface and has a period of 433 days. In 1899, to measure the Chandler Wobble or variation of latitude, the International Geodetic Association established the International Latitude Service, made up of several dedicated observatories located along a common parallel of latitude, including the Gaithersburg Latitude Observatory. These observatories used identical Zenith Telescopes and observed sets of stars each night. In 1962 the International Latitude Service was reorganized into the International Polar Motion Service, adding many new observatories at different latitudes and several types of instruments. By 1980, other methods, particularly interferometry, satellite laser ranging, and the Global Positioning System, were able to track changes in the Earth's orientation in space far better than the classical optical instruments used at the IPMS stations.

Gaithersburg, Maryland · United States