Aristarchus

 By: Allyson Fitzgibbons

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=Aristarchus = =310-230B.C. =

**__ Background __**

Aristarchus of Samos is one of the many astronomers that made a significant difference in the world we live in and how we believe it works. Aristarchus, born in Samos, Greece, lived from about 310-230 BC. Because he was from an ancient time, there is not much knowledge about his individual life, but luckily there is enough information to credit him with a few theories and discoveries. One way that we know when Aristarchus lived is that he is said to be a pupil of [|Strato of Lampsacus], who succeeded another man at the Peripatetic School in approximately 288 BC.(2) In addition, Aristarchus made an observation of the summer solstice in 288/287 BC and he published a book, "On the Sizes and Distances of the Sun and Moon," before Archimedes’, providing helpful input to the dates of his life.(2) Aristarchus was a man of many talents, known as both an astronomer and a mathematician and he was one of the last Ionian scientists.(3) There is little left of Aristarchus’ work, since what remained was located at the Alexandrian Library.(3) Archimedes, along with some other astronomers, passed on Aristarchus’ legacy with enough information that everyone can acknowledge his many achievements.


 * __ Accomplishments __**

One of the less-known works of Aristarchus was a new version of a [|sun dial].(2) It used shadows, “enabling the direction and the height of the sun to be read of by means of lines marked on the surface of the hemisphere."(2) In addition to this mechanical triumph, Aristarchus also wrote about vision, light, and color. With Stato’s guidance, he believed that colors were “shapes or forms stamping the air with impressions like themselves as it were” and that colors in darkness actually have no coloring.(2) Though these thoughts are important and at the time, groundbreaking, Aristarchus’ achievements go far beyond.

One of the most significant theories that Aristarchus proclaimed was the heliocentric model of the universe. He was the first man to suggest that the Sun is at the center of the planetary system, and that all planets go around the Sun rather than the Earth, which represents the geocentric model. (3) Aristarchus’ explanation that the Earth rotated around the Sun gave a more natural explanation for [|retrograde motion] than what’s given for a geocentric model of the universe. Retrograde motion is when an object, like a planet, seems to move backwards from the norm. The planets never actually change direction, as it seems if you viewed from Earth, it just appears that way.(1)



 It is commonly known that it wasn’t until the time of Copernicus that anyone gave much thought to the possibility of a heliocentric model of the universe, but he was not the first to think of it. Copernicus continued Aristarchus’ idea of a heliocentric universe and proved it in the Copernican Revolution . If Aristarchus’ beliefs had not been thwarted by Aristotle and others, Aristarchus may have been given more credit and more attention in today’s history. Some of Aristotle’s problems with Aristarchus’ work were as follows:
 * 1) “If the Earth actually spun on an axis (as required in a heliocentric system to explain the diurnal motion of the sky), why didn't objects fly off the spinning Earth?
 * 2) If the Earth was in motion around the sun, why didn't it leave behind the birds flying in the air?
 * 3) If the Earth were actually on an orbit around the sun, why wasn't a parallax effect observed? That is, stars should appear to change their position with the respect to the other background stars as the Earth moved about its orbit, because of viewing them from a different perspective (just as viewing an object first with one eye, and then the other, causes the apparent position of the object to change with respect to the background).”(4)



The first two objections were proven false when a better understanding of the physics of motion were provided in the 17th century.(3) The third, however, was more complicated. The Greeks figured that if the Earth did in fact orbit around the Sun, “at different times of the year we would be closer to different parts of the celestial sphere and would notice changes in the angular separations of stars.”(1) The answer is that the stars are so far away that stellar parallax is undetectable.(1) He believed the stars were fixed and “only appeared to move because of Earth’s rotation on its axis."(5) These facts seemed farfetched to the ancient Greeks though, and Aristarchus’ ideas were deemed unreliable.

In addition to suggesting a heliocentric model of the universe, Aristarchus made significant accomplishments having to do with the sizes and distances of some of the very important figures in our solar system. One achievement rewarded to Aristarchus is estimating the sizes of the Moon and Sun. For the Moon, Aristarchus observed the “shadow of Earth on the Moon during a [|lunar eclipse].”(1) From this observation, he estimated that the Moon’s diameter was approximately one-third of Earth’s diameter, which is only “slightly” larger than the actual quantity. (1) Using geometry, Aristarchus then estimated the Sun’s and moon’s distances. He accomplished this by “measuring the apparent angle between the Earth and Sun during the first quarter Moon, when the Moon-Sun angle is 90 ° .” (5) Aristarchus’ experiment was mathematically valid, but it was very difficult to pinpoint the exact moment when the Moon was 50% illuminated.(5) This stood as an obstacle because the slightest difference could render strenuous errors in the results. (5) <span style="color: black; font-family: 'Georgia','serif'; font-size: 12pt;">Aristarchus’ results, which were that the angle was 87 °, led him to project that the Sun was twenty times as far from the Earth as the Moon, and therefore twenty times larger. This observation may have led to his heliocentric theory because he reasoned that such a large body like the Sun is absurd to orbit such a small one like the Earth. (3) <span style="color: black; font-family: 'Georgia','serif'; font-size: 12pt;">The actual size of the Earth-Sun-Moon angle is 87 ° 50’though, which makes the Sun actually four hundred times as far from the Earth. (5) <span style="color: black; font-family: 'Georgia','serif'; font-size: 12pt;">Even though Aristarchus’ results were incorrect, he still proved that the Sun was much farther than the Moon from Earth. --> ** the following is a video on how to estimate the size of the Sun like Aristarchus: media type="youtube" key="zioSpV2yq24" height="323" width="400" align="center" <span style="color: #000000; display: block; font-family: 'Georgia','serif'; font-size: 12pt; line-height: 115%; text-align: left;">Although Aristarchus was the first astronomer to suggest that the planets orbit the Sun and not Earth, it is very probable that he drew some of his ideas from even earlier intellectuals. Heracleidas had suggested that the Earth rotates and Pythagoras that the Earth in fact moves.(1,5) Aristarchus likely continued these ancients’ thoughts in order to make his highly significant prediction regarding our universe. Although much of what Aristarchus wrote has been lost, there is no doubt that his ideas live on. We have only to look at Nicholas Copernicus and his revolutionary findings. There is even a crater on the Moon named Aristarchus in honor of the scholar. The work of Aristarchus will never be overlooked and he will always be remembered for his essential contributions to the world of science.

<span style="font-family: Georgia,serif;">**__ Sources __**

<span style="font-family: Georgia,serif;">~__Sources of pictures in order of appearance on page__: <span style="font-family: Georgia,serif; font-size: 11pt; line-height: 115%;"> []

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~References
 * 1) <span style="font-family: Georgia,serif;">Bennett, Jeffrey, Megan Donahue, Nicholas Schneider, and Mark Voit. //The Cosmic Perspective//. 6th ed. San Francisco: Addison-Wesley, 2010.
 * 2) <span style="font-family: Georgia,serif;">Heath, Thomas. //Aristarchus of Samos//. Oxford: Clarendon, 1913.
 * 3) <span style="font-family: Georgia,serif;">Sagan, Carl. //Cosmos//. New York: Random House, 1980. Print.
 * 4) <span style="font-family: Georgia,serif;">[]
 * 5) <span style="font-family: Georgia,serif;">Moore, Patrick. //Astronomy Encyclopedia//. New York: Oxford UP, 2002. Print.