Invariant (physics) Note: Invariance, does not imply not varying, it pertains to a condition where there is no variation of the system under observation, and the only applicable condition, is the instantaneous condition. Invariance pertains to now(). Now(+1), to a condition where all variations are solely due the internal variables, with no external aspects imparting nor removing energy (Newton´s law of motion: a system in motion continues in motion, unless an external force imparts or removes energy). That condition is met by using the partial derivative function, ∂f(internal)xf(external) and presuming/setting f(external)=constant, leading to ∂f(external)=1 using the chain rule. Obviously, this is a model used solely for calculations, and not a reality. In the current era, the immobility of Polaris (the North Star) under the diurnal motion of the celestial sphere is a classical illustration of physical invariance. Quantities can be invariant under some common transformations but not under others.
Celestial sphere. In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with a particular celestial body. All objects in the observer's sky can be thought of as projected upon the inside surface of the celestial sphere, as if it were the underside of a dome or a hemispherical screen. The celestial sphere is a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant.
Introduction[edit] For some objects, this is over-simplified. Objects which are relatively near to the observer (for instance, the Moon) will seem to change position against the distant celestial sphere if the observer moves far enough, say, from one side of the celestial body to the other. The celestial sphere can be thus be thought of as a kind of astronomical shorthand, and is applied very frequently by astronomers. Celestial coordinate systems[edit] History[edit] Star globe[edit] See also[edit] Celestial coordinate system. In astronomy, a celestial coordinate system is a system for specifying positions of celestial objects: satellites, planets, stars, galaxies, and so on.
Coordinate systems can specify a position in 3-dimensional space, or merely the direction of the object on the celestial sphere, if its distance is not known or not important. Coordinate systems[edit] Horizontal system[edit] The horizontal, or altitude-azimuth, system is based on the position of the observer on Earth, which revolves around its own axis once per sidereal day (23 hours, 56 minutes and 4.091 seconds) in relation to the "fixed" star background. The positioning of a celestial object by the horizontal system varies with time, but is a useful coordinate system for locating and tracking objects for observers on earth.
It is based on the position of stars relative to an observer's ideal horizon. Equatorial system[edit] The equatorial coordinate system is centered at Earth's center, but fixed relative to distant stars and galaxies. Or. Astronomische Koordinatensysteme. Koordinatensystem des Horizonts, nördliche Erdkugelhälfte Koordinatensystem des Orts-Äquators, nördliche Erdkugelhälfte Astronomische Koordinatensysteme dienen dazu, die Position von Himmelskörpern anzugeben. Dabei handelt es sich um Kugelkoordinaten, im engeren Sinne um sphärische Koordinaten, weil für das Finden der Körper am Himmel deren Entfernung keine Rolle spielt. Koordinatenursprung der astronomischen Systeme ist die Erde (ihr Mittelpunkt oder ein Ort auf ihrer Oberfläche, geozentrisches Weltbild), die Sonne (heliozentrisches Weltbild) oder ein anderer Himmelskörper (zum Beispiel ein Planet, um die Lage seiner Monde relativ zu ihm selbst anzugeben). Das Horizont-System ist das Koordinatensystem, das jedem Beobachter am vertrautesten ist.
Relative Koordinatensysteme[Bearbeiten] Relative Koordinatensysteme sind die an einen Beobachter gebundenen. Absolute Koordinatensysteme[Bearbeiten] Winkel-Angaben in Stunden anstatt in Grad[Bearbeiten] Übersichtstabelle[Bearbeiten] α = θ - ττ = θ - α. Astronomische Koordinatensysteme.