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The spheres thus moved with a "natural nonviolent motion". [33] The mover's power diminished with increasing distance from the periphery so that the lower spheres lagged behind in their daily motion around the Earth; this power reached even as far as the sphere of water, producing the tides. [34] [35]
Taking the distance of the Sun as 1,266 Earth radii, he was forced to place the sphere of Venus above the sphere of the Sun; as a further refinement, he added the planet's diameters to the thickness of their spheres. As a consequence, his version of the nesting spheres model had the sphere of the stars at a distance of 140,177 Earth radii. [34]
The ancient Greeks assumed the literal truth of stars attached to a celestial sphere, revolving about the Earth in one day, and a fixed Earth. [9] The Eudoxan planetary model , on which the Aristotelian and Ptolemaic models were based, was the first geometric explanation for the "wandering" of the classical planets . [ 10 ]
The horizontal, or altitude-azimuth, system is based on the position of the observer on Earth, which revolves around its own axis once per sidereal day (23 hours, 56 minutes and 4.091 seconds) in relation to the star background. The positioning of a celestial object by the horizontal system varies with time, but is a useful coordinate system ...
Eudoxus's model was geocentric, with the Earth being a stationary sphere at the center of the system, surrounded by 27 rotating spheres. [4] The farthest sphere carried stars, which he declared to be fixed within the sphere. Thus, though the stars were moved around the Earth by the sphere which they occupied, they themselves did not move and ...
The ecliptic is the plane which contains the orbit of a planet, usually in reference to Earth. Elongation refers to the angle formed by a planet, with respect to the system's center and a viewing point. A quadrature occurs when the position of a body (moon or planet) is such that its elongation is 90° or 270°; i.e. the body-earth-sun angle is ...
Astronomers believed that the seven naked-eye planets (including the Moon and the Sun) were carried around the spherical Earth on invisible orbs, while an eighth sphere contained the fixed stars. Motion was provided to the whole system by the Primum Mobile, itself set within the Empyrean, and the fastest moving of all the spheres. [5]
This small difference in the Sun's position against the stars causes any particular spot on Earth's surface to catch up with (and stand directly north or south of) the Sun about four minutes later each day than it would if Earth did not orbit; a day on Earth is therefore 24 hours long rather than the approximately 23-hour 56-minute sidereal day ...