Sphere armillaire

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.
An external mechanism of orientation also comprising two circles:
  • the horizon of the place
  • the Meridian local
A foot is used as general support with the unit.

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.

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