Percival Period 5
Astronomy
October 10 2013
Astronomy Project
Eudoxus of Cnidus:
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Being born around the year 390 B.C.E., Eudoxus was a man of great knowledge that led to his famous model of the planets and the basic 5 ideas of space. A man of various capabilities, such as in Math, metaphysics, ethics, and astronomy, Eudoxus began to travel throughout Europe, learning under others who proved their brilliance such as Plato and Archytas. With the influences of his teacher, Eudoxus begins to delve into the subjects and make new discoveries that affect us to this very day.
During his life, Eudoxus advanced in math as he made the theory of proportions which allowed him to compare irrational numbers and his method of exhaustion which allowed him to find the area of a polygon.
His major influence in astronomy came from his teacher Archytas. Following his teacher's beliefs of the solar system, Eudoxus, like many others, believed that the sphere was the perfect shape. He made many observations of the stars and sky which he incorporated into the school he made to teach all the subjects he excelled in and became very popular due to that. One of his accomplishments was his creation of the first five basic principles of the celestial world:
1. The Earth is the center of everything.
2. Planets and orbits are all circular.
3. All celestial movement is regular
4. The center of a celestial object when it is moving is also its center.
5. The center of all things is the center of the universe
Eudoxus not only believed in the homocentric view he also made the first model incorporating his concept of how planets and celestial objects moved called the homocentric sphere system. He pictured his model as the Earth being the inner central sphere encompassed by the 27 spheres which represent the Sun, the Moon and five planets orbiting the Earth. He believed that the outer most sphere (what Eudoxus thought were fixed stars) controlled the rotation of Earth, however, each consecutive sphere has a different rotation around its sphere. Eudoxus saw that in his model of two spheres a figure eight structure called the hippopede appeared. This is where a planet would pass the curve of a sphere. He placed a third sphere to represent the motion of the planet corresponding to the seemingly fixed stars in the sky as the planet went in a retrograde motion seen in many planets. Finally Eudoxus made a sphere to show the daily rotation of the fixed stars. In the end, the homocentric sphere system contained 27 spheres; this revelation became a huge geometrical accomplishment at his time.
His discovery had influenced the famous Aristotle who took the concept of spheres literally when it is argued that Eudoxus really meant for it to be just a model to represent the paths of the planets.
His works also influenced Hipparchus, a Greek mathematician, in 2 of his books which included Eudoxus’ measurements of the rising and the setting times of certain constellations which shows the broad range of the effects Eudoxus had on math and astronomy today.
Callippus:
Born in the year 370 BC, Callippus was a Eudoxus’ student at the school which Eudoxus constructed. During his life, Callippus, with the help of Aristotle, took Eudoxus’ homocentric sphere model and modified the system by adding 7 more spheres which in turn allowed him to accurately measure celestial orbits. Callippus, throughout his life had consulted with Aristotle and worked for him as well, adding on to his experience and knowledge of astronomy.
Callippus is also known for his precise measurements of the lengths of seasons and his construction of a 76 tropical year cycle compromising 940 solar and lunar months which are used by astronomers to this day. He also found a more precise measurement of the tropical year of 365.25 days rather than just 365 days which is now accepted world-wide.
All of Callippus’ findings have and are still being used for accurate measurements of our planets and stars presenting his influence on all the astronomical theories today.
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