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Our Universe
There are many different theories on how the
universe started. The most widely accepted is called The Solar Nebula Theory.
It states that our solar system was probably formed out of a spinning ball of gas. When
the sun became luminous enough, the remaining dust and gas were blown away into space,
leaving the planets orbiting the sun. This took place about 4.5 billion years ago.
The planets move around the sun in orbits that lie nearly in a commpn plane, and they all
revolve about the sun in the same direction (counter-clockwise as seen from their north
pole).
By the process of condensation the heavier gasses moved inward to the center of the
nebula, and the lighter gasses were pushed outward. This resulted in two types of planets,
the Terrestrial planets, like Earth, and Jovian planets, like Jupiter. Mercury, Venus,
Earth, and Mars are Terrestrial planets. Jupiter, Saturn, Uranus, and Neptune are Jovian
planets.
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