Solar system
The new definition of the name of a desired planet by the executive of the International Astronomical Union (IAU) officially our Solar System has 8 planets, downgrading Pluto to the status of dwarf planet. This new definition was adopted by members of the Planet Definition Committee, a committee set up by the IAU to reflect on what a planet in light of recent discoveries both within our Solar System as around d other stars.
The main celestial body of the Solar System is the Sun, a yellow dwarf star of the main sequence of type G2 that contains 99.86% of the known mass of the solar system and gravitationnellement14 dominates. Jupiter and Saturn, the two most massive objects orbiting the Sun, together account for over 90% of the remaining mass.
Most large objects in orbit around the Sun are in a plane close to that of Earth's orbit, called the ecliptic. Typically, the orbital plane of the planets is very close to the ecliptic while comets and Kuiper belt have mostly an orbit that form a significantly greater angles to it.
All the planets and most other objects orbit in the same direction as the rotation of the sun, that is to say anticlockwise from an observer standpoint located above the solar north pole. Some objects orbit in a retrograde direction, as Halley's Comet.
The trajectories of objects orbiting around the Sun following Kepler's laws. They are approximately ellipses with one focus is the sun. The orbits of the planets are nearly circular. Those smaller bodies have various eccentricities and can be highly elliptical. This is particularly the case of some comets and other small bodies, some dwarf planets and more generally of trans-Neptunian objects including the Kuiper belt and the Oort cloud.
The distance of a body from the Sun varies during its rotation around the sun. Called the closest point to the Sun to the orbit of a body perihelion, the farthest being its aphelion.
Informally, the Solar System is often divided into separate zones. The inner Solar System includes the four terrestrial planets and the asteroid belt. The rest of the system may be regarded merely as externe15 Solar System; other separate the region beyond Neptune of four giant gazeuses16.
The majority of planets in the solar system have their own school system. Planetary rotating body around a planet are called natural satellites or moons. Most of the largest natural satellites fly in a synchronous orbit, always presenting the same face to the planet around which they revolve. The four largest planets also have a planetary ring.
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