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The innermost spheres are the terrestrial spheres, while the outer are made of aether and contain the celestial bodies. In Plato's Timaeus (58d) speaking about air, Plato mentions that "there is the most translucent kind which is called by the name of aether (αἰθήρ)" [9] but otherwise he adopted the classical system of four elements.
In Greek antiquity the ideas of celestial spheres and rings first appeared in the cosmology of Anaximander in the early 6th century BC. [7] In his cosmology both the Sun and Moon are circular open vents in tubular rings of fire enclosed in tubes of condensed air; these rings constitute the rims of rotating chariot-like wheels pivoting on the Earth at their centre.
[4] For example, if a TNO is incorrectly assumed to have a mass of 3.59 × 10 20 kg based on a radius of 350 km with a density of 2 g/cm 3 but is later discovered to have a radius of only 175 km with a density of 0.5 g/cm 3 , its true mass would be only 1.12 × 10 19 kg.
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]
Plato and Aristotle helped to formulate the original theory of a sublunary sphere in antiquity, [4] the idea usually going hand in hand with geocentrism and the concept of a spherical Earth. Avicenna carried forward into the Middle Ages the Aristotelian idea of generation and corruption being limited to the sublunary sphere. [ 5 ]
S 3: a 3-sphere is a sphere in 4-dimensional Euclidean space. Spheres for n > 2 are sometimes called hyperspheres. The n-sphere of unit radius centered at the origin is denoted S n and is often referred to as "the" n-sphere. The ordinary sphere is a 2-sphere, because it is a 2-dimensional surface which is embedded in 3-dimensional space.
Visualization of a celestial sphere. In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth.All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer.
This system consisted of the four classical elements of air, earth, fire, and water, in addition to a new theory called the sulphur-mercury theory of metals, which was based on two elements: sulphur, characterizing the principle of combustibility, "the stone which burns"; and mercury, characterizing the principle of metallic properties.