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Coordinate systems in astronomy can specify an object's relative position in three-dimensional space or plot merely by its direction on a celestial sphere, if the object's distance is unknown or trivial. Spherical coordinates, projected on the celestial sphere, are analogous to the geographic coordinate system used on the surface of Earth.
One particularly distant body is 90377 Sedna, which was discovered in November 2003.It has an extremely eccentric orbit that takes it to an aphelion of 937 AU. [2] It takes over 10,000 years to orbit, and during the next 50 years it will slowly move closer to the Sun as it comes to perihelion at a distance of 76 AU from the Sun. [3] Sedna is the largest known sednoid, a class of objects that ...
The two most commonly used systems are the Stonyhurst and Carrington systems. They both define latitude as the angular distance from the solar equator, but differ in how they define longitude. In Stonyhurst coordinates, the longitude is fixed for an observer on Earth, and, in Carrington coordinates, the longitude is fixed for the Sun's rotation.
Objects farther from the Sun are composed largely of materials with lower melting points. [44] The boundary in the Solar System beyond which those volatile substances could coalesce is known as the frost line, and it lies at roughly five times the Earth's distance from the Sun. [5]
The first satellites designed for long term observation of the Sun from interplanetary space were NASA's Pioneers 6, 7, 8 and 9, which were launched between 1959 and 1968. These probes orbited the Sun at a distance similar to that of Earth, and made the first detailed measurements of the solar wind and the solar magnetic field.
A parsec is the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond (not to scale). The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles).
This is independent of the distance of the star from the Earth. Annual parallax – the apparent change in position due to the star being viewed from different places as the Earth orbits the Sun in the course of a year. Unlike aberration, this effect depends on the distance of the star, being larger for nearby stars.
Absolute magnitudes for Solar System objects are frequently quoted based on a distance of 1 AU. These are referred to with a capital H symbol. Since these objects are lit primarily by reflected light from the Sun, an H magnitude is defined as the apparent magnitude of the object at 1 AU from the Sun and 1 AU from the observer. [10]