A planet is a celestial body that revolves around a star and that becomes visible by the light of it is reflected. In the case of the solar system that star is the Sun.

The International Astronomical Union defines planets like celestial bodies that revolve around the sun, with a mass sufficient to take hydrostatic balance by gravity, which have cleared the vicinity of its orbit.

Major planets

The Solar System is made up of eight planets, which revolve around the sun. These planets depending on their proximity to the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Pluto is an exception because the International Astronomical Union (IAU) is classified as a dwarf planet according to the agreement made on 24 August 2006.

Planets depending on the distance to the Sun

This is the main way to differentiate the planets, and can be found:

·  Inner Planets: are those who have a distance to the Sun with the Earth below. These are planets Mercury and Venus.

·  Outer Planets are those planets whose distance from the sun is greater than with the Earth as Mars, Jupiter, Saturn, Uranus and Neptune.

Planets according to their characteristics

Another way to differentiate planets is according to their surface and characteristics which have given rise to:

·  Terrestrial Planets or telluric are those that have a rocky surface and solid and its density is high like Mercury, Venus, Earth and Mars.

·  Planets jovianos: have large diameters, formed by gas and low density. They are part of this type of planets Jupiter, Saturn, Uranus and Neptune, the giant planets.

Planets according to their movements in the sky

They may be classified according to the movements performed in the sky:

Planets below: are those who do not depart from the Sun and therefore are unable to show opposition. In this group are Mercury and Venus.

Planets above: they can get away from the sun reaching to oppose him. Mars, Jupiter, Saturn, Uranus and Neptune are planets of this kind.

Remarks

The inner and outer planets should not be confused with the planets upper and lower since the behavior of the latter was due to its distance from the Earth.