Running head: THE HISTORY OF OUR KNOWN UNIVERSE

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THE HISTORY OF OUR KNOWN UNIVERSE The history of our known universe At one time, it was believed that the earth was the center of the universe and that all

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celestial bodies revolved around the earth. This belief was so deeply held that complicated orbits of the planets were created in order to ensure that the earth remained at the center. Anyone that dared to challenge the earth center model was immediately considered a heretic and faced very serious consequences. Can you imagine the kind of world that we would live in today if great thinkers did not challenge the common thought of the time? Aristotle was a very famous Greek philosopher. Aristotle subscribed to the belief that the earth was the center of the universe and that all celestial bodies orbited around the earth in perfect circles known as Epicycles (Dept. Physics & Astronomy University Of Tennessee, n.d.) . In order to ensure that the earth remained at the center of the universe, complicated models of the movements of the planets were created. Eventually, this model, created in 150 A.D., came to be known as the Ptolemaic Universe. This model called for the planets to move in perfect circles around the earth. Because the perfect circles did not account for the strange movement of the planets, the planets were made to move in smaller circles (epicycles) as they moved around the earth. More and more Epicycles were added to accommodate the strange movement of the planets. While the Ptolemaic Universe model was able to explain many of the strange movements of the planets, it was complicated and difficult to implement. However, the Ptolemaic Universe model was widely accepted and it remained so for 2000 years. In the 16th century, a Polish Astronomer named Nicolai Copernicus challenged the Ptolemaic Universe Model. Copernicus suggested that the Earth was not the center of the universe but rather, the sun was. Copernicus did not completely challenge Ptolemaic model of the universe. While he believed that the planets all orbited the sun, he also believed that the

THE HISTORY OF OUR KNOWN UNIVERSE planets orbited the sun in perfect circles. It would be another 100 years before the work of Copernicus was accepted. However, it was the great work of Copernicus that led us to the understanding that we have of our solar system today.

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A nobleman by the name of Tycho Brahe is credited for inventing a device that allowed him to measure the movement of the planets more accurately than had ever been done before. In particular, Brahe accurately measured the movement of Mars. It is the collection of this data that allowed Brahe’s assistant to make one of the most remarkable discoveries of the time. Brahe’s assistant was a gentleman by the name of Johannes Kepler. It was Kepler that understood the data that was collected by Brahe. In particular, Kepler analyzed the data that Brahe collected regarding the orbit of Mars. Kepler correctly realized that the orbit of the planet was not a perfect circle, as previously thought. Instead the orbit of Mars was elliptical. This was a profound discovery because it meant that, for the first time, the orbits of the planets could be explained without the need for epicycles. This discovery also meant that the Earth was not at the center of the universe. Earth was part of a group of planets circling the sun. On January 7th 1610 Galileo pointed a telescope, for the first time, at the night sky. Galileo did not invent the telescope but he was the first to use it to look at the heavens. While Galileo’s telescope was crude compared to today’s standards, it allowed him to see the universe in action. He saw sunspots, the moons of Jupiter, craters on our own moon, the Milky Way, and much more. It was as Galileo was viewing the stars near Jupiter that he made an astonishing discovery! One of the stars disappeared! Galileo reasoned that it must have disappeared because it was now behind Jupiter and if the star was behind the planet, then it must be in orbit around Jupiter. Galileo then came to the conclusion that the earth was not the center of the universe as

THE HISTORY OF OUR KNOWN UNIVERSE was the common belief for so many centuries. Unfortunately, Galileo’s findings did not sit well with the church. It is important to note that all of the astronomers (or thinkers) to this point conducted their work during medieval times. The Catholic Church had a strangle hold on everyone from

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Peasants to Kings. If the church did not approve of it, it simply was not so. Following a path that was against the teachings of the Church was not tolerated and there were dire consequences for those that attempted it. The Catholic Church proclaimed that the earth was the center of the universe, that the orbits of the planets were perfect circles, that all celestial bodies orbited the earth, and that the stars were in a fixed position beyond the planets. Imprisonment, torture, or death was the sentence that could be handed down to anyone that dared to oppose the church (Alchin, 2006). The church believed that what Galileo was doing was the work of the devil. In fact, Galileo was thrown in jail and forced to recant what he learned about the universe. Sir Isaac Newton is known as the father of modern day physics and astronomy. It is the work of Newton that allows us to send men to the moon! Newton gave us the three laws of Motion: – First law: The velocity of a body remains constant unless the body is acted upon by an external force. – Second law: The acceleration of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma. – Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear. In fact, Newton’s third law “The mutual forces of action and reaction between two bodies are equal, opposite, and collinear” (essentially, this means that for every action there is an equal and

THE HISTORY OF OUR KNOWN UNIVERSE opposite reaction) was put to the test by astronaut Eugene Cernon in July 1966. Eugene was

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tasked to find out of humans could work in the zero gravity of space (Http://www. Youtube.com, n.d.) . When Eugene tried to perform even the most simplest tasks, he found that he was propelled one way or the other. If he tried to turn a valve, his body would turn in the opposite direction. Eugene was exhausted by the time he was pulled back into the space craft. However, Newton’s third law was affirmed. Newton also speculated that if a canon ball were shot out of a canon, with a might force, that it could shoot past the Earth’s horizon and continue to go around the Earth. The canon ball would achieve an orbit around the earth! Much like the moon that orbits our planet this very day. In fact, this very theory was put to the test on 4 October 1957. Russia launched the very first satelite called sputnik.

THE HISTORY OF OUR KNOWN UNIVERSE References Alchin, L.K. (2006, September). Middle Ages. Retrieved November 24, 2011, from http://www.middle-ages.org.uk/ Dept. Physics & Astronomy University Of Tennessee (n.d.). Astronomy 161: the Solar System. Retrieved November 7, 2011, from http://csep10.phys.utk.edu/astr161/lect/index.html http://www. Youtube.com (n.d.). Newton's Third Law of Motion: Astronauts in Outer Space. Retrieved November 7, 2011, from http://www.youtube.com/watch?v=PrJnWTcW55s

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