In Astronomy, a sphere armillaire , so known under the name of spherical Astrolabe , is a modeling based on the celestial Sphère used to show the apparent movement of it star S around the Ground and Sun in the ecliptic.
Its name comes from the Latin armilla (circle, bracelet), since it consists of a whole of graduated metal circles representing the geometry of the descriptive elements of the sky, on the directional central sphere:
- the pole S,
- the axis of the poles
- the parallel S private individuals which are the equator, 2 polar circles and the 2 Tropique S.
- the ecliptic , apparent way traversed by the Sun in the sky, marked out by the Constellation S zodiacales.
- sometimes the Splicing S of the solstices and the equinoxes, celestial meridian lines passing by the ecliptic positions of the Sun at the beginning of the Season S.
- generally, a ball representing the Earth is placed in its center on the axis of the poles.
- the horizon of the place
- the Meridian local
The spheres armillaires were developed by the former Greeks and were already used like didactic tools at third century BC. In a larger and more precise form they were also used like instruments of observation, in particular by Ptolémée. The spheres armillaires became again popular at the end of the Moyen-âge; the astronomer Danish Tycho Brahe built several of them. The sphere armillaire was also known in China, since Zhang Heng (78 - 139 AD) until Su Song which conceived in 1088 a sphere armillaire actuated by a mechanism Hydraulique.
The portraits of the scientists and the personalities of the Renaissance often show those with a hand on a sphere armillaire which then represents the top of knowledge and wisdom. Currently recognized like the symbol of the universe.
The spheres armillaires were among the first built complex mechanical apparatuses; their development made many improvements in the technique and the design of parts and mechanical equipment.
A representation of the sphere armillaire is found on the Drapeau of Portugal like symbol of its old maritime power.
|Random links:||El proyecto de la bruja de Blair | Spéos | Munshausen | Christian August Crusius | Cosmic meeting (play) | Posistor|