Geocentric
Cross-traditionAstronomical factEditorial synthesis
Definition
Measured from the centre of the Earth. A geocentric position describes where a body appears from here: a choice of viewpoint, not a claim that the Earth is the centre of the solar system.
Also called: Earth-centred · Geocentric frame
In more depth
Any celestial position has to be measured from somewhere, and the answer changes with the viewpoint. Heliocentric coordinates are measured from the centre of the Sun; geocentric coordinates are measured from the centre of the Earth. Modern ephemerides compute the underlying motions in a solar-system frame and then transform them to whichever centre the caller asks for.[1]
Astrology is geocentric because it describes the sky as seen from Earth, which is where the observer stands. Saying a chart is geocentric is a statement about the frame of reference, and carries no implication that the Earth is physically central; the heliocentric structure of the solar system is not in question here.[2]
References
Numbered citations in the text link to the records below; each record links to the full source registry.
- Ryan S. Park; William M. Folkner; James G. Williams; Dale H. Boggs. The JPL Planetary and Lunar Ephemerides DE440 and DE441. The Astronomical Journal 161 (3), article 105. 2021. Astronomical fact View source record
- NASA Science. Basics of Space Flight, Chapter 2: Reference Systems. current (living reference page). Astronomical fact View source record