A planet is a spherical ball of rock and/or gas that orbits a star. Our solar system has 8 planets; in order of increasing average distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The International Astronomy Union has an official definition for a planet. It states, "A 'planet' is defined as 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 neighborhood around its orbit." Pluto is a dwarf planet.
Planets and Galaxies
Planets and Galaxies
Planets and Galaxies
Planets and Galaxies
Planets and Galaxies
Planets and Galaxies
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