The Universe
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9. The Heliocentric Universe

Figure 10.5 The Heliocentric model
At the beginning of the 16th century A.D., Nicolaus Copernicus proposed that Earth and all the other planets orbit the Sun.

With the Sun at the centre, this model is called the heliocentric model, or "sun-centered" model.

Although Copernicus’ model was simpler, it still did not perfectly describe the motion of the planets.

Johannes Kepler solved the problem a short time later when he determined that the planets moved around the Sun in ellipses (ovals), not circles . Kepler’s model matched observations perfectly.

The heliocentric model did not catch on right away.

When Galileo Galilei first turned a telescope to the heavens in 1610, he made several striking discoveries. Galileo discovered that the planet Jupiter has moons orbiting around it.

This provided the first evidence that objects could orbit something besides Earth.

Galileo’s discoveries caused many more people to accept the heliocentric model of the Universe, although Galileo himself was found guilty of heresy.

The shift from an Earth-centered view to a Sun-centered view of the universe is referred to as the Copernican Revolution.

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