Aristarchus
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Around 300BC lived Aristarchus. A Greek astronomer and mathematician. He would become the father of astronomy. He lived on the island of Samos. He deduced by observation that a lunar eclipse and was in fact the shadow on the moon was the Earth! From this he realised that the Moon orbited the Earth. He then noted that the Earth must then be orbiting the Sun. This was contrary to theories put abroad by Aristotle and Ptolemy, other so called enlighted people. It would be another 1800 years before Copernicus revived this theory after which Kepler and Newton added their considerable might to the theory through the laws of physics, namely Kepler's laws for the motion of planets and Newton's laws on gravitational attraction and dynamics. Galileo added his few pence worth when, on observing Jupiter, he noted 'three faint stars' nearby. Then he saw four! He soon realised that these were in fact moons circling the planet. HERE were astronomical bodies orbiting something that was not the Sun, contrary to Church indoctrination of that time. Religion really does retard knowledge and curiosity. Copernicus, who knew of Aristarchus' work, is generally recognised as the principle player in this theory, nothing could be further from the truth. Being far ahead of his time, like his younger contemporary Archimedes, his ideas never seem to have developed a following and so died out until the telescope revived them. Unfortunately, the original work in which Aristarchus proposes the theory has been lost; we know of it because Archimedes refers to it and describes Aristarchus' proposals. His results were only limited by the accuracy of the measurements of his day, which suffered from a lack of technology.
Aristarchus began with the premise that, during a half moon, the moon forms a right triangle with the Sun and Earth. By observing the angle between the Sun and Earth, φ, the ratio of the distances to the Sun and Moon could be deduced using a form of trigonometry. Links lead to Wikipedia details.
The diagram is greatly exaggerated, because in reality, S = 390 L, and φ is extremely close to 90°. Aristarchus determined φ to be a thirtieth of a quadrant (in modern terms, 3°) less than a right angle: in current terminology, 87°. Trigonometric functions had not yet been invented, but using geometrical analysis in the style of Euclid, Aristarchus determined that: In other words, the distance to the Sun was somewhere between 18 and 20 times greater than the distance to the Moon. This value (or values close to it) was accepted by astronomers for the next two thousand years, until the invention of the telescope permitted a more precise estimate of solar parallax. Aristarchus also reasoned that as the angular size of the Sun and the Moon were the same, but the distance to the Sun was between 18 and 20 times further than the Moon, the Sun must therefore be 18-20 times larger. I don't pretend to understand much of these mathematics, but the discovery he made speaks volumes for the man. One of the most prominent craters on the lunar surface is named after Aristarchus, in my humble opinion, the whole moon should be renamed in his honour. He is, after all, the father of astronomy. Why does every moon in the solar system have a name, and not our own? Aristarchus will be a most suitable name.
The heliocentric model did not originate with Copernicus. As with so many scientific ideas – including basic theories of evolution and the atom – Greece was the origin. First proposed by Aristarchus in the second century BC, it was later promoted by Copernicus in the sixteenth century. The model placed the Sun at the centre of the solar system, and relegated the Earth to be just one of the planets orbiting the Sun, with all the orbits supposed to be circular.
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