A Solar System can be defined as a star and all the objects orbiting it as well as all the material in that system. Our solar system includes the Sun together with the eight planets and their moons as well as all other celestial bodies that orbit the Sun.
From our small world we have gazed upon the cosmic ocean for thousands of years. Ancient astronomers observed points of light that appeared to move among the stars.
They called these objects planets, meaning wanderers, and named them after Roman deities -- Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the goddess of love and beauty; and Saturn, father of Jupiter and god of agriculture.
The stargazers also observed comets with sparkling tails, and meteors -- or shooting stars apparently falling from the sky.
Since the invention of the telescope, three more planets have been discovered in our solar system: Uranus (1781), Neptune (1846) and Pluto (1930). Pluto was reclassified as a dwarf planet in 2006. In addition, our solar system is populated by thousands of small bodies such as asteroids and comets. Most of the asteroids orbit in a region between the orbits of Mars and Jupiter, while the home of comets lies far beyond the orbit of the dwarf planet Pluto, in the Oort Cloud.
The four planets closest to the sun -- Mercury, Venus, Earth, and Mars -- are called the terrestrial planets because they have solid rocky surfaces. The four large planets beyond the orbit of Mars -- Jupiter, Saturn, Uranus, and Neptune -- are called the gas giants.
Beyond Neptune, on the edge of the Kuiper Belt, tiny, distant, dwarf planet Pluto has a solid but icier surface than the terrestrial planets.
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