The Planets

The International Astronomical Union (IAU) defines a planet in our Solar System as follows:
“A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.”

According to this definition, there are eight major planets in our solar system. These are:

The Planets - relative sizes
The planets of our Solar System showing relative sizes

See also:

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Astronomy, Cosmology, Space and Astrophysics