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  2. Geocentric model - Wikipedia

    en.wikipedia.org/wiki/Geocentric_model

    Pages from 1550 Annotazione on Sacrobosco's De sphaera mundi, showing the Ptolemaic system. In the Ptolemaic system, each planet is moved by a system of two spheres: one called its deferent; the other, its epicycle. The deferent is a circle whose center point, called the eccentric and marked in the diagram with an X, is distant from the Earth.

  3. Barycentric and geocentric celestial reference systems

    en.wikipedia.org/wiki/Barycentric_and_geocentric...

    The geocentric system is simpler, being smaller and involving few massive objects: that coordinate system defines its center as the center of mass of the Earth itself. The barycentric system can be loosely thought of as being centered on the Sun, but the Solar System is more complicated. Even the much smaller planets exert gravitational force ...

  4. Astronomical coordinate systems - Wikipedia

    en.wikipedia.org/.../Astronomical_coordinate_systems

    The geocentric ecliptic system was the principal coordinate system for ancient astronomy and is still useful for computing the apparent motions of the Sun, Moon, and planets. [3] It was used to define the twelve astrological signs of the zodiac , for instance.

  5. Deferent and epicycle - Wikipedia

    en.wikipedia.org/wiki/Deferent_and_epicycle

    The orbits of planets in this system are similar to epitrochoids, but are not exactly epitrochoids because the angle of the epicycle is not a linear function of the angle of the deferent. In the Hipparchian system the epicycle rotated and revolved along the deferent with uniform motion.

  6. Planetary coordinate system - Wikipedia

    en.wikipedia.org/wiki/Planetary_coordinate_system

    Chart of lunar maria with lines of longitude and latitude. The prime meridian is the centre of the near side of the Moon.. A planetary coordinate system (also referred to as planetographic, planetodetic, or planetocentric) [1] [2] is a generalization of the geographic, geodetic, and the geocentric coordinate systems for planets other than Earth.

  7. Equatorial coordinate system - Wikipedia

    en.wikipedia.org/wiki/Equatorial_coordinate_system

    The positions of the planets and other Solar System bodies are often specified in the geocentric equatorial rectangular coordinates ξ, η, ζ and a fourth distance coordinate, Δ (equal to √ ξ 2 + η 2 + ζ 2), in units of the astronomical unit.

  8. Primum Mobile - Wikipedia

    en.wikipedia.org/wiki/Primum_Mobile

    In classical, medieval, and Renaissance astronomy, the Primum Mobile (Latin: "first movable") was the outermost moving sphere in the geocentric model of the universe. [ 1 ] The concept was introduced by Ptolemy to account for the apparent daily motion of the heavens around the Earth, producing the east-to-west rising and setting of the sun and ...

  9. Celestial spheres - Wikipedia

    en.wikipedia.org/wiki/Celestial_spheres

    In Aristotle's fully developed celestial model, the spherical Earth is at the centre of the universe and the planets are moved by either 47 or 55 interconnected spheres that form a unified planetary system, [19] whereas in the models of Eudoxus and Callippus each planet's individual set of spheres were not connected to those of the next planet ...