Latitude exact relationship of parallels and meridians with horizontal and vertical: both are complicated curves. On the sphere the normal passes through the centre and the latitude () is therefore equal to the angle subtended at the centre by the meridian arc from the equator to the point concerned. If the meridian distance is denoted by then where denotes the mean radius of the Earth. is equal to . No higher accuracy is appropriate for since higher-precision results necessitate an ellipsoid model. With this value for the meridian length of 1 degree of latitude on the sphere is (60.0 nautical miles).
International Latitude Observatory International Latitude Observatory The International Latitude Observatories were a system of (originally) 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. The original six observatories were located in: The International Latitude Service was created by the International Geodetic Association in 1899 to study the precession, or "wobble" of the Earth's axis, and its effect on measures of latitude. Six separate observatories were created along the parallel 39° 08' north latitude. The alignment of all