Chobotov, V.A. (2002). Orbital Mechanics. AIAA Education Series. American Institute of Aeronautics & Astronautics. p. 72. ISBN978-1-60086-097-3. Retrieved October 24, 2021.
National Geospatial Intelligence Agency. "World Geodetic System 1984 datasheet"(PDF). United Nations Office for Outer Space Affairs. United Nations. Retrieved December 16, 2021.