Anaxagoras
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Anaxagoras was a Greek astronomer who, around c. 450 B.C., discovered that the moon does not generate its own light, as had been believed previously. Anaxagoras realized that the moon's light is actually a reflection of the sun's light. In addition, Anaxagoras believed that everything in the universe was made up of smaller particles, and that these particles rearranged themselves to create different things. Anaxagoras was born in Asia Minor, but spent a large portion of his life in Athens, studying the heavens.
Democritus
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Democritus was another early Greek philosopher. He was born in Abdera, in Northern Greece. Along with Anaxagoras, Democritus also believed that matter was composed of smaller particles that we cannot see. Democritus called these particles atoms. Democritus believed that the world was composed of an infinite number of atoms, and that different combinations of these atoms created different things. Democritus also believed that everything that we hear, see, feel, smell, or taste is just atoms coming in contact with sense organs. He stated that "true knowledge" comes from the mind, rather than the senses.
Aristarchus
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Aristarchus was a Greek astronomer who was born around 310 B.C. and lived until about 230 B.C. Aristarchus was extremely important to Greek astronomy because, before him everyone, even the brightest of philosophers and scientists, believed that the Earth was the center of the universe. Aristarchus was the first to state that the Earth actually revolved around the sun, instead of the other way around. This idea may seem very obvious to astronomers today, however the very notion was not even considered, (at least publicly), until Aristarchus came around. No one knows for certain how exactly Aristarchus came to this conclusion, however his idea was quoted by the famous mathematician, Archimedes.
Aristotle
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The ancient Greeks believed that the Earth was the center of the universe. They believed that the
other objects in the universe were part of spheres that revolved around the Earth. The sun, the moon, and the other five known planets, each had their own spheres. Furthermore, all of the stars were part of one sphere. These spheres all revolved around the Earth, but each sphere also affected the revolution of the others. Aristotle, an ancient Greek philosopher, slightly altered the astronomical beliefs of ancient Greece, stating that there were actually 56 spheres, many more than the Greeks initially theorized. Another difference in Aristotle’s thinking was that he believed that these so-called “spheres” were not imaginary, but were made of an actual clear substance called “aither”. Aristotle believed that a single force called the Prime Mover made the last sphere, the sphere full
of stars, rotate and then set the rest of the spheres in motion. As far as Aristotle's background goes, he was born in 384 B.C. in northern Greece and was the star student at the Academy, a school taught by Plato, a very well-known philosopher.
other objects in the universe were part of spheres that revolved around the Earth. The sun, the moon, and the other five known planets, each had their own spheres. Furthermore, all of the stars were part of one sphere. These spheres all revolved around the Earth, but each sphere also affected the revolution of the others. Aristotle, an ancient Greek philosopher, slightly altered the astronomical beliefs of ancient Greece, stating that there were actually 56 spheres, many more than the Greeks initially theorized. Another difference in Aristotle’s thinking was that he believed that these so-called “spheres” were not imaginary, but were made of an actual clear substance called “aither”. Aristotle believed that a single force called the Prime Mover made the last sphere, the sphere full
of stars, rotate and then set the rest of the spheres in motion. As far as Aristotle's background goes, he was born in 384 B.C. in northern Greece and was the star student at the Academy, a school taught by Plato, a very well-known philosopher.
Hipparchus
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Hipparchus was a Greek astronomer who lived from about 180 B.C. to approximately 125 B.C. Hipparchus was born in Nicaea, near present-day Turkey. Hipparchus is famous for discovering the movement of the equinoxes. The equinoxes are the points where the sun's path crosses the celestial equator, which is an imaginary line in the sky above the equator. Hipparchus noticed that the stars had slightly shifted position over many years, and he explained this shift in position as an extremely gradual movement of the equinoxes. Also, Hipparchus is known for measuring how long it takes for the moon to go through its stages of waxing and weaning. Coupled with other calculations, these measurements helped Hipparchus to be able to predict eclipses more accurately than ever before.
Ptolemy
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Possibly the most reputable of all Greek astronomers was Ptolemy, a Greek man who resided in Alexandria, Egypt. In the A.D. 100’s, Ptolemy took astronomy to a whole new level, both
agreeing and disagreeing with Aristotle and other astronomers. First, Ptolemy disagreed with Aristarchus in that he was confident that the Earth did not revolve around the sun, but that everything revolved around the Earth. Ptolemy agreed that there were spheres
in the universe that moved the stars and planets, because, at the time, there
was no other reasonable way to describe the motion of the heavens. It was completely sensible to leave some of the work of previous scientists and philosphers unchallenged. However, Ptolemy disagreed with Aristotle in that he argued that these spheres were not composed of an actual, physical substance, but rather that they were an imaginary thing, such as the equator. In reality, there is not a line that runs around the perimeter of the Earth, but people still know where the equator is. It was a similar situation with these astronomical spheres. Also, Ptolemy created a system for observing the heavens that was much more intricate and complicated than any system before, but his methods seemed unquestionable to the people of Ptolemy’s time, and to the people for over 1,000 years after Ptolemy’s passing. Finally, in the late Middle Ages, new minds decided to challenge Ptolemy’s theories.
agreeing and disagreeing with Aristotle and other astronomers. First, Ptolemy disagreed with Aristarchus in that he was confident that the Earth did not revolve around the sun, but that everything revolved around the Earth. Ptolemy agreed that there were spheres
in the universe that moved the stars and planets, because, at the time, there
was no other reasonable way to describe the motion of the heavens. It was completely sensible to leave some of the work of previous scientists and philosphers unchallenged. However, Ptolemy disagreed with Aristotle in that he argued that these spheres were not composed of an actual, physical substance, but rather that they were an imaginary thing, such as the equator. In reality, there is not a line that runs around the perimeter of the Earth, but people still know where the equator is. It was a similar situation with these astronomical spheres. Also, Ptolemy created a system for observing the heavens that was much more intricate and complicated than any system before, but his methods seemed unquestionable to the people of Ptolemy’s time, and to the people for over 1,000 years after Ptolemy’s passing. Finally, in the late Middle Ages, new minds decided to challenge Ptolemy’s theories.