Trojan (celestial body) Trojan (celestial body) In astronomy, a trojan is a minor planet or moon that shares the orbit of a planet or larger moon, wherein the trojan remains in the same, stable position relative to the larger object. In particular, a trojan remains near one of the two trojan points of stability – designated and – which lie approximately 60° ahead of and behind the larger body, respectively. Trojan points make up two of five types of Lagrangian points, and a trojan is a type of Lagrangian object. They are one type of co-orbital object. In this arrangement, the massive star
Celestial sphere 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. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location. The celestial sphere is a practical tool for spherical astronomy, allowing astronomers to specify the apparent positions of objects in the sky if their distances are unknown or irrelevant. In