Science 9: Unit E: Space Exploration Topic 1 – For Our Eyes Only

A Brief History of the Universe The Ancient Greeks  The Ancient Greeks believed that the universe was split into two parts: the imperfect Earth and the prefect, unblemished sky made up of the sun, moon, stars, and five planets.

Ancient Greeks Cont’d  The Greeks believed that the sun was actually their god Apollo riding in a fiery chariot. To help make sure the sun rose up everyday you had to pray to Apollo and offer sacrifice. Events such as a solar eclipse were interpreted that the Greeks had offended Apollo somehow.  Everything worked like clockwork in the sky except for the five planets, which didn’t follow any pattern. Sometimes the planets rose at night other times in the morning, sometimes they moved left, other times they moved right. The Greeks just assumed that the planters were special and gave them the names of their gods: Mercury, Venus, Mars, Jupiter, and Saturn. Planet means wanderer in Greek.

Geocentric Model  Means Earth-centred.  Eventually the idea that the sun was a chariot for Apollo became offensive and silly to the Greeks and Romans, so a new, more scientific model was created, the Geocentric Model.  The Geocentric Model is made of the following ideas:  1. The Earth was the center of the universe. Everything orbited the Earth.  2. The sun, moon, and planets moved around the Earth because they were attached to invisible shells, which turned around the Earth pulling the objects with them.  3. The planets were special because their movements changed over time. They changed direction and speed in the sky so they were given epicycles: little circles that they would spin around while still being attached to their invisible shells.

Geocentric Model

 This model nearly perfectly explained how and why everything moved in the sky. People were satisfied with this model even though it was complicated. It lasted over 1500 years with no problems. It became the accepted model for the Western World.

The Heliocentric Model  Means sun-centred  In the early 1500s a Polish priest, Nicholas Copernicus, created a new model which put the sun at the center of the universe and made the Earth a planet orbiting the sun. This model was called the Heliocentric Model. This was very controversial and not very well accepted by the Catholic Church.  100 years later, Italian scientist Galileo used telescopes to study the moon and planets. He discovered that the moon is not perfect, but full of craters and ridges, so the perfect heavens were not so perfect after all.

Heliocentric Model Cont’d  Galileo also discovered five moons orbiting around Jupiter. This was the first proof of something NOT orbiting around the Earth. This made the Heliocentric model more believable and accepted.

Heliocentric Model