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Astronomical history 1. Dreamtime story Complete the sentences: The Warlpiri Aboriginal people explained a solar eclipse as the result of the moon-man being threatened by the sun-woman who is pursuing him and catching up. The solar and lunar eclipse dreamtime stories demonstrate that aboriginal people had an understanding that eclipses were caused by a relationship between the sun and the moon. 2. Ptolemy Claudius Ptolemy (85−165) developed a model of the universe. (a) Use the diagram to describe Ptolemy’s model of the universe. Ptolemy’s theory of earth place in the universe was called a geocentric model. This means that he thought that the earth was at the centre of the universe. This also explained to the people about how in religion “god” had made the earth perfect everything revolving around them. (b) Where did Ptolemy place the stars in his model? In this model Ptolemy places the stars outside of the revolving planets. The sun is an example being the first star in our solar system and being the furthest away eluding to that the stars were placed outside of our solar system. (c) Ptolemy knew that Mars moved across the sky in a looping motion called retrograde motion. His model explained this motion using epicycles. Use the diagram below left to explain the idea of epicycles; label the diagram below right where necessary. Ptolemy was the first astronomer to figure out why planets would revolve backwards. He called this an epicycle. Planets move in and orbit around the sun and also in a circle on that line (shown in the second picture). When this epicycle theory happens it is thought that the earth being on a smaller rotation it catches up on say Mars’s rotation it appears to the naked eye it is revolving backwards Retrograde motion Page 2 3. Copernicus Nicolaus Copernicus (1473−1543) was a Polish astronomer who proposed a radically different model of the universe. List from center of diagram 1. Sun 2. Mercury 3. Venus 4. Earth 5. Mars 6. Jupiter 7. Saturn (a) Where did Copernicus place the sun in his model? Copernicus placed the sun in his new theory at the centre of the solar system. He called this with the help of Galileo a heliocentric model of the universe. (b) Label the diagram above to show the position of the sun and the six known planets. (c) How did Copernicus explain day and night and the length of a year using his model? Copernicus explained that day and night happened when the one side of the earth rotated and did not face the light of the sun. He explained a year happening when the earth did a full rotation around the sun. 4. Galileo Galileo Galilee’s (1564−1642) observations of Jupiter over successive nights revealed four starlike objects in a line with it. The objects moved from night to night, sometimes disappearing behind or in front of the planet. (a) Identify the bodies that Galileo had observed. Galileo observed these four bodes and came to the conclusion that these where exactly like the earth’s moon and how it rotated. So he defined them as the four moons of Jupiter (b) Explain how his observations of Jupiter supported the Copernican model and not the Ptolemaic model of the universe. Galileos observations helped strengthen Copernicus heliocentric model by proving that the four moons of Jupiter were not revolving around the earth but around Jupiter. Later Isaac Newton came to discover that this was the result of Gravity.