Preliminary Physics Assessment Task 1 Christos Toras   MODELS OF THE UNIVERSE -

Aristotle’s model by today’s standards can easily be picked apart, but at the time, it was the best explanation that could be made with so little technology and insight. Although his theories have long since been replaced, they created a base for future scientists to work off of and challenge. Over time many great scientists began to question Aristotle’s theories. Nicolaus Copernicus (1473-1543), for example, contested the absolute significance of the earth, and he did not agree that it should be viewed as the center of the entire universe (Lizhi & Youquan, 1987). He plotted the earth at the center of the universe and created a heliocentric system just as mathematically complicated as the Ptolemaic system (one that also improved on Aristotle’s), but it explained a number of anomalies, including resolving the issue of retrograde motion (Ede, A. & Cormack, L., 2004). The problem was that Aristotle’s physics of ‘natural motion’ fell apart without the earth in the center of everything.

During the first millennium B.C. scientists realized that astronomy had to become more scientific. Middle Eastern and Chinese cultures started studying the Sun, stars and the planets more closely in an attempt to learn more about our position in the universe.. Star positions also became important tools in understanding directions, and helping with navigation. One philosopher stated in 434 B.C. that the Sun was a ball of fire 60 kilometres in diameter, hovering 6500 kilometres above Earth’s surface. Around 130 B.C., Ptolemy wrote Almagest, which was a huge collection of astronomical data which included mathematical models, information about eclipses, and planetary and stellar positions and movements. It remained a major go to book for astronomy for hundreds of years, and was not seriously challenged until Copernicus disputed the geocentric model of the solar system in the 1500’s

Among these people were Copernicus who believed the sun was at the center of the world and the earth, stars and planets revolved around it. Danish astronomer Brahe helped contribute to this idea by contributing a large mass of data about the universe that he was able to discover. His student Kepler kept his ideas going, as he formulated many laws of planetary motion. He said the orbits around the sun were elliptical, planets don’t move in a uniform speed and the time a planet completes its orbit is related to its distance from the sun. Meanwhile, Florentine Galileo decided to use experiments to find out what happened and not what should happen, and discovered that a uniform force makes a uniform acceleration as well as inertia laws, that an object will be in motion forever unless stopped by another force.

the heliocentric solar system. Johannes Kepler further modified the heliocentric system, by mathematically showing that the planets’ orbits are elliptical. With his invention of the telescope, Galileo made new observations about the solar system and found mathematical laws that described the movement of the planets. Later, Isaac Newton established a universal law of gravity. With the new scientific discoveries, the gap between religion and science increased. Science revolutionized the human though and its understanding of the universe.

Copernicus published "On the Revolutions of the Celestial Spheres" in 1543 , sparking off the scientific revolution and a new era of astronomical thought. This theory explains that the sun, not the Earth, is the center of the solar system and planets move in a circular motion around it. This had many social, intellectual and religious made of huis idea. For instance, this theory brought into question the strict reading of the Bible and philosophies of the Catholic Church.

When it comes to theories and law’s concerning the movement of stellar bodies and why the universe is moving the way it is and how it came to be, data is continuously being added and revised. It is through this constant revising of theories and establishing of laws that core ideas are proven, with modern day scientists expanding knowledge for the rest of us. One of the earliest pioneers of spatial theories was the Italian astronomer, Galileo Galilei, who used the theories of those who came before and he learned from to paint a better picture of the way the universe was set. True to form, he dealt with accusations of heresy and resistance to his ideas from others during his life, which today are held as being before his time.

1. Why was the Ptolemaic system accepted as an explanation of celestial motion for over a thousand years? What did it explain? What system challenged the idea that Earth was the center of the universe?

Nicholas Copernicus was the first to question the universal truths and teachings of the church. He devised a theory that the earth along with the other planets revolved around the sun. This theory disagreed with Aristotle and the old teachings that the universe revolved around the earth, and that man was the center of the universe.

Throughout time people have held different ideas of what the universe looks like, from the Aristotelian universe centered around the Earth to the Copernican universe with our Sun at the center. After Sir Isaac Newton invented physics,

Aristotle had refuted heliocentricity , and by Galileo's time nearly every major thinker subscribed to a geocentric view. Copernicus had delayed the publication of his book for years because he feared not the censure of the Church, but the mockery of academics. It was the hide-bound Aristotelians in the schools who offered the fiercest resistance to the new science. Aristotle was the Master of Those Who Know; perusal of his texts was regarded as almost superior to the study of nature itself. The Aristotelian universe comprised two worlds, the superlunary and the sublunary. The former consisted of the moon and everything beyond; it was perfect and

The geocentric view of the universe, first introduced to the world in about 150 CE, was thought to be the undoubted correct model of what the universe looked like. The theory described the Earth as the center of the universe, with stars and planets orbiting around it. According to Carl Sagan, an American astronomer and cosmologist, “This [the geocentric view] is the most natural

(Frova 41) Galileo’s confirmation of Copernican’s heliocentric theory explained through logical arguments and mathematical laws clearly the answers to these difficulties.

The classical 2-sphere model was rooted in Aristotelian framework consisting of a “spherical universe at the center of which was the spherical Earth.” (Dear 10). Aristotle’s viewpoint of the universe was divided into terrestrial and celestial with all the terrestrial elements consisting of Earth, Wind, Fire and Air. What distinguished the celestial region was the heavens which surrounded “the earth by transparent, invisible spheres” (Dear 11) made of aether that Aristotle classified as uniform in motion. His universe was also finite with a definite end point. In comparison, Ptolemy’s Almagest suggested the planets move in circular eccentric motions by combining math and data to make

His first law states, “The orbits of the planets are ellipses, with the Sun at one focus of the ellipse.” As shown in Figure 1, The Sun is not at the focus of the ellipse, but is instead at one focus [usually there is nothing at the other focus of the ellipse]. The planet then trails the ellipse in its orbit, which implies that the Earth-Sun distance is continually changing as the planet goes around its orbit. Kepler’s second law states, “The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse.” As shown in Figure 2, an imaginary line from the center of the sun to the center of a planet sweeps out the same area in a given time. This means that planets move faster when they are closer to the sun. Kepler’s third and final law states, “The time taken by a planet to make one complete trip around the sun is its period. The ratio of the squares of periodic times for two planets is equal to the ratio of the cubes of their mean distances from the sun.” Kepler’s third law indicates that the time taken by a planet to orbit the Sun increases quickly with the radius of its orbit ("Johannes Kepler: The” 1-4). Kepler’s laws challenged Aristotelean and Ptolemaic astronomy. His statement that the Earth

After Tycho’s death, his assistant, young mathematician Johannes Kepler used Tycho’s observations and came up with his First Law that orbits of the planets are elliptical instead of round like Copernicus believed. With his Second Law, Kepler stated that the speed of the planets depends on their distance from the sun which helped English astronomer and physicist Isaac Newton, to come up with his Law of Universal Gravitation.