Planets

Planets are celestial bodies orbiting a star. In our Solar System, the eight planets Mercury, Venus, Earth, Mars, Jupiter, Saturn Uranus and Neptune orbit around the Sun. These planets form part of what is known as the solar system which also contains other objects such as asteroids and comets.

The term “planet” was first used by ancient Greeks in their skywatching observations to refer to these wandering stars that were different from fixed stars (stars). The most important criteria for calling an object a planet is its ability to clear its orbital path of other material while keeping some kind of gravitational balance with nearby objects; this criterion has been referred to since 2006’s International Astronomical Union resolution on planetary definition as “dynamic stability” or being able “clear its neighbourhood” over time scales up to several billions years. This means any body large enough not only be gravitationally bound by another but whose gravity can dominate all neighbouring bodies must be designated a planet even if it orbits something else than the sun like Pluto does when it orbits Charon or binary systems where two stars orbit each other closely like Kepler-16b does when orbiting both stars A and B at once . It excludes smaller “minor planets” such as asteroids dwarf planets (like Ceres)and cometary nuclei which do not follow longterm stable paths through space due either size or lack of gravity compared against larger neighbours .

The four innermost planets (Mercury -Mars) are rocky terrestrial worlds composed mostly out iron silicates whereas outer gas giants Jupiter -Neptune have predominantly gaseous atmospheres made largely hydrogen helium with relatively small solid cores hidden beneath thick layers atmosphere All eight excepting earth rotate counterclockwise viewed from north pole hence they share same direction rotation compared moon rotates clockwise opposite them because tidal forces exerted early history impelled change direction rotation relative sun

Planets come in many sizes shapes colors composition depending distance location origin Solar System For example smallest largest discovered date respectively mercury jupiter however recent discoveries exoplanet kepler 452b suggest possibility potentially massive superjovian beyond theoretical limits traditional classifications thus defining exact boundaries between classes objects difficult task current day astronomers continue refine definitions differentiate characteristics qualities assign new names categories discoverings