THALES of Miletus (624-560 B.C.).

Astronomer, mathematician and philosopher. Learned astronomy from the Babylonians. Founder of the Ionian school of natural philosophy. Predicted the solar eclipse on May 28, 585.

Inopedes (Chios, 400 B.C. ).

Greek astronomer. Believed to have first calculated the angle the Earth is tipped with respect to the plane of its orbit. He found the value of 24 degrees which differs only half degree from the presently accepted value.

Diogenes of Apollonia (425 B.C.)

Diogenes was a pupil of Anaximenes, whom he followed in making air the primary element of all things but regarded that there was an intelligent principle behind the order of the Universe. He wrote a number of books on Cosmology.

Tycho Brahe (1546 – 1601)

Chronicled supernova of 1572 and discovered it had no diurnal parallax proving it lay beyond the Moon, plotted the motion of the comet of 1577, accurately plotted motions of planets used by Kepler after his death.

Archylas of Tarentum (420-350 B.C.).

Greek mathematician, astronomer and engineer. Last of the Pythagorians. Plato and Eudoxus was his pupils. Built a series of toys, among them a mechanical pigeon propelled by a steam jet. Developed the theory for the pulley.

GALILEO Galilei (1564-1642)

Resolved the stars in the Milky Way, discovered sunspots and measured the Sun’s rotation, observed Venus phases, discovered four moons of Jupiter, observed lunar features and measured lunar wobble, supported the Copernican system of planetary movement via his observations.

Heracleides (390-320 B.C.).

Greek astronomer. First to suggest that Venus and Mars may orbit the sun. Also suggested the the Earth rotates around its axis once every 24 hours.

CONON (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.

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.

PTOLEMY Claudius (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

Hipatias (3rd - 4th century A.D.).

Last ancient philosopher and astronomer.

COPERNICUS Nicolaus (1473 – 1543)

Proposed Earth orbited the Sun via De Revolutionibus Orbium Coelestium contradicting the long held Ptolomic belief that the Sun orbited the Earth thereby laying the groundwork for Galileo and Kepler.

KEPLER Johannes (1571 – 1630)

Using Brahe’s precise data derived his three laws of planetary elliptical motion, provided explanation of optical image formation through small apertures, the first enunciation of the inverse square law for intensity of illumination.

HALLEY Edmond (1656 – 1742)

Astronomer Royal, discovered Omega Centauri, paid for publishing Newton’s Principia, using Newton’ gravitational law predicted the comet of 1682 would return in 76 years, invented the idea of using transits of Mercury and Venus to determine distance to the Sun.