Although relatively little is known about Aristarchus of Samos, he is considered one of the greatest astronomers and
mathematicians of the Alexandrian period. He is considered the father and founder of astronomy as a scientific
discipline, for he attempted to employ scientific reason and logic in the understanding of the heavens in lieu of
religious beliefs and doctrines in existence at the time.
Aristarchus is best known for having put forth the heliocentric theory when describing the motion of the heavenly bodies whereby the planets orbit about a stationary sun in independent orbits. More specifically, Aristarchus proposed that the stars and sun are fixed in space wheres the planets, including earth, had their motion composed of two components comprised of a daily rotation about an axis and an annual rotation about the sun.
Aristarchus emphasized that the sphere containing the stars was infinitely larger than the corresponding sphere which contained the orbit of the earth around the sun and, thus, the stationary nature of the stars in the sky could be explained. These revolutionary thoughts were instrumental in having Aristarchus accused of blasphemy (286 BC) and forced to flee to Alexandria in order to avoid the death penalty and where he taught at the Lyceum until his death. There are numerous direct and indirect references to Aristarchus' heliocentric theory including the writings of Archimedes who wrote:
"... Αρίσταρχος δε ο Σάμιος υποθεσίων τινών εξέδωκεν γραφάς, εν αις εκ των υποκειμένων συμβαίνει τον κόσμον πολλαπλάσιον είμεν του νυν ειρημένου, υποτίθεται γαρ τα μεν απλανέα των άστρων και τον άλιον μένειν ακίνητον, ταν δεν γαν περιφέρεσθαι περί τον άλιον κατά κύκλου περιφέριαν, ος έστιν εν μέσω τω δρόμω κείμενος"
and which when translated (see O'Connor and Robertson) reads:
"... Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the 'universe' just mentioned. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit"
Regrettably, the geocentric model would remain the established theory for many centuries due to religious reasons and only until Copernicus (1473-1543) decided to adopt and reincarnate the work of Aristarchus seventeen centuries later would humanity changes its perspective on celestial mechanics, particularly as it relates to the motion of the planets.
In addition to the work described above, Aristarchus of Samos also attempted to estimate the size of the moon and sun as well as their distance using geometry and, more specifically, the first quarter phase of the moon which yields an almost right-angle triangle between the earth, moon and sun. Using an assumption of a 3° angle between the sun and earth when the moon is at first quarter, he estimated the sun to be 20 times more distant from earth than the moon as well as 20 times larger. Although these estimates are in error by an order of magnitude due to the lack of accurate tools at the time, they nevertheless reveal the ingeneous geometrical approach taken to deduce these relative distances and sizes in conjunction with the observation that the sun and moon have a nearly identical apparent diameter (evident during an eclipse).
Aristarchus has been honored by having a crater and rima (rille) on the northwest quadrant of the moon named after him (see Rukl: 18). Crater Aristarchus (23.7° N, 47.4° W), measuring 40-km in diameter with steep slopes and 3 km high, is the brightest crater on the moon and is visible during earthshine. It forms an impressive pair with Crater Herodotus to its immediate west and is best observed during an eleven-day or twenty-four-day old moon. Similarly, Rima Aristarchus (26.9° N, 47.5° W) lies to the northeast of Crater Aristarchus and comprises of approximately eight rille networks measuring approximately 121 km in length and 1.5 km in width. A wide-field view of this area is available elsewhere on this site (see here and here) with an additional high-power view available here.
For a thorough discussion on the life and ingenious work of Aristarchus of Samos, the reader is referred to: