Hellinistic/Alexandrian period (4th century B.C. - 5th century A.D.)

This period marking advances in astronomy, mathematics and medicine. Hellinistic refers to the Greeks and others who lived after Alexander the Great's conquests, during which there existed a mixture of civilizations. Important schools of this period include Epicurianism, Stoiciscm, and Skeptisicm.

Philosophers-Scientists

• Epicurus of Samos (341-270 B.C.). Founder of the philosophical school of Epicurianism which, similar to the Atomists, believed that atoms are fundamental parts of the real world. Believed that fate was governed by laws of nature and not some mysterious gods.
• Straton (Lambsacus, 340-290 B.C.). Greek physicist. Conducted experiments leading him to discover that bodies accelerate when they fall. However, erroneously, he also believes that heavier bodies fall faster. Also studied the lever, but does not find it's law. His work emphasizes the use of experimentation for scientific research. Lived in Alexandria, then moved to Athens to head the Aristitle's Lyceum after Theophrastos.
• Zenon of Citius (4th century B.C.). Formed the Stoic school. Had a large number of interesting astronomical beliefs, which include the earth is limited and sherical, beyond earth there is an infinite void, the stars rotate with the sky.
• Euclid (Alexandria, 4th - 3rd century B.C.). Alexandrian mathematician. Author of Elements, a set of twelve volume that portrayed the geometric thought of the Greeks as it developed in the 6th to 4th century B.C. It includes plane and solid geometry, the theory of incommensurables, and the theory of numbers. Like Plato, he disregarded practicality.
  Links: Euclid of Alexandria, University of St Andrews, Scotland, Euclid, Encyclopedia Britannica
• Aristarchus of Samos (310-230 B.C.). Proposed that the sun is at the center of the universe with Earth along with the other planets circulating around it. He estimated the distance of the sun from the Earth by observing the angle between the sun and the moon when it is exactly half full.
• Archimedes (Syracuse, 287-212 B.C.). Greek mathematician and engineer which is included among the top ranking mathematicians in history. Also a natural philosopher. He demonstrated that all numbers can be written down, by writing down the number of grains of sand needed to fill the entire universe. He expertly used the method of exhaustion developed by Eudoxus. He found ratios of the volumes of various figures, such as that of a sphere and a cylinder with a height equal to the diameter of the sphere which is equal to two thirds. He was the first to apply mathematical laws to levers. He is also known for his discovery that a body immersed in fluid displaces an amount of fluid equal to its own mass. Legend has it that he discovered this while in the bath and later ran naked around the streets of Syracuse shouting Eureka (I have found it). He used levers to pull a fully loaded ship on shore, thus supporting his statement: "give me a lever long enough and a place to stand and I can move the Earth". According to legend he was killed by a soldier while contemplating geometric figures drawn in the sand, even though the soldier's commander had ordered Archimedes' life spared.
  Links: Chris Rorres' Archimedes Web Page (Drexel University), Archimedes of Syracuse, University of St Andrews, Scotland, Archimedes, Encyclopedia Britannica
• Ktisibios (Alexandria, 285-222 B.C). Engineer. Formed the so called Engineering School. Together with his pupul Philon, Heron, and Archimedes where the most famous engineers of ancient times.
• Eudemus of Rhodes (340 B.C.). Student of Aristotle. Wrote the History of Mathematics, which is lost, and the History of Astronomy.
• Conon (Samos, 283-222 B.C.). Greek mathematician and astrnomer. Headed the Alexandrian library after Euclid. Discovered a new stellar formation that he named Come (or Plocamos) Berenices, in honor of Berenice, queen of Ptolemaios III Evergetes.
• Eratosthenes of Cyrene (276-200 B.C.).. Greek astronomer and mathematician. Calculated the circumference of the Earth and finds a figure of 46,000 km which is close to the present measured value. Also lays down the first lines of longitude on a map of Earth. He also developed a method for calculating all prime numbers: the sieve of Eratosthenes.
• Apollonius of Perga (262-190 B.C.). Mathematician that did a significant amount of work on the conics (circle, ellipse, parabola, and hyperbola). His work was summerized in his book Conics. Considered the last great synthetic geometer until the end of the eighteenth century.
• Philon of Byzantine (3rd - 2nd century B.C.). Engineer.
• Theodosios (2nd century B.C.).
• Hipparchus of Nicea (190-120 B.C.) Greek astronomer and mathematician. Considered the greatest astronomer of ancient times. Developed a system of planetary motion with the Earth at the center. This system was later refined by Ptolemy. Used data from a total eclipse of the sun and parallax to determine correctly the distance and size of the moon. The same data gave values for the distance and size of the sun an order of magnitude smaller than there actual values. Compiled the first tables of cord length, forerunner of trigonometric tables.
• Seleucus (Seleucia, 190-??? B.C.). Last known astronomer to champion the heliocentric theory of the solar system until Copernicus.
• Poseidonius (Apamea, 140-50 B.C.). Incorrectly calculated the Earth's circumference, which 1500 year later, led Columbus to believe that Asia was only about 3000 miles west of Europe.
  Links: Poseidonius, Encyclopedia Britannica
• Diocles (180 B.C.). Investigates properties of the curve he names cissiod (meaning ivy).
• Hypsicles (180 B.C.). Greek mathematician. It is believed that Hypsicles introduced the 360 degree circle to Greek mathematics.
• Sosigenes (1st century B.C.). Greek astronomer and mathematician. His advice to Julius Caeser led to the adoption of the Julius calendar, which stayed in effect until 1578 when it was changed by Pope Gregory XIII.
• Heron (Alexandria, 1st century B.C.). Engineer.
• Andronikos of Kyrrhestes (50 B.C.). Built, in Athens, the Tower of Winds, a water clock combined with solar clocks, the most famous time-keeping device of the Greeks.
• Menelaos (Alexandria, 1st - 2nd century A.D.). Astronomer and Mathematician.
• Ptolemy Claudius (Alexandria, 127-145 A.D.). Last great Alexandrian astronomer. Refined the system of planetary motion developed by Hipparchus, which had Earth at the center of the universe, known as the "Ptolemaic System". Best known for his Almagest
  Links: The Universe Viewed by People of Ancient Times
• Diophantos (250 A.D.). Considered the father of geometry.
• Papos (3rd century A.D.).
• Hipatias (Alexandria, 3rd - 4th century A.D.). Last ancient philosopher and astronomer.