armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (on the celestial sphere), consisting of a spherical framework of rings, centred on Earth or the Sun, that represent lines of celestial longitude and latitude and other astronomically important features, such as the ecliptic.

Source: Italian

Plural: Armillarji


Orbital mechanics or astrodynamics:the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. The motion of these objects is usually calculated from Newton’s laws of motion and law of universal gravitation. It is a core discipline within space-mission design and control.


Astrophysics: the branch of astronomy that employs the principles of physics and chemistry “to ascertain the nature of the astronomical objects, rather than their positions or motions in space”. Among the objects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background



Spherical astronomy or positional astronomy: the branch of astronomy that is used to determine the location of objects on the celestial sphere, as seen at a particular date, time, and location on Earth. It relies on the mathematical methods of spherical geometry and the measurements of astrometry.