450s BC

Astronomy

Philosopher Empedocles [b. Akragas, Sicily, c. 492 bce, d. Mount Etna, c. 432 bce] proposes that eclipses of the Sun are caused by the Moon coming between Earth and the Sun. See also 520 bce Astronomy.

Greek philosopher Oenopides [b. Chios, Greece, c. 490 bce, d. c. 420 bce] calculates the angle that Earth is tipped with respect to the plane of its orbit (an angle apparent to anyone who regularly watches the stars -- it is not necessary to assume that Earth travels in a path around the Sun). His value of 24° is only half a degree from the presently accepted value of 23.5° and will be used until Eratosthenes refines it to the more precise value.

An ironworking industry develops in Great Britain. See also 500 bce Materials.

Although early Greek temples were constructed of sun-baked brick and wood, marble eventually replaces these materials, although at first the marble is treated in much the same way as the earlier brick -- stuccoed over and painted. About this time an excellent source of marble is found on Mount Pentelicus, a short distance north of Athens, enabling Greek builders to construct the famous white marble buildings and statues of the Acropolis. Because such marble can be cut in beams up to 4.5 m (15 ft) long, Greek architects do not need to utilize arches, corbels, or domes on roofs, sticking mostly with post and lintel construction.

Greek historian Herodotus of Halicarnassus (Turkey) [b. 484 bce, d. c. 425 bce] explores the Middle East, Babylon, and Persia about this time and gives the first description of cotton, which he finds in India. See also 3000 bce Food & agriculture.

The Greeks develop a method of writing numbers based on letters of the alphabet. See also 3100 bce Mathematics.

Empedocles recognizes that the heart is the center of the system of blood vessels, but wrongly concludes that this organ must also be the seat of the emotions, a notion that was accepted by many later Greek writers and that has persisted in folk tradition ever since. See also 275 bce Medicine & health.

Greek philosopher Protagoras [b. Abdera (Spain), c. 490 bce, d. c. 420 bce] believes that sense perceptions are all that exist, so that reality may be different from one person to another. See also 440 bce Physics.

Empedocles of Akragas introduces a system in which fire, air, earth, and water are the elemental substances that can undergo change through the action of two opposing forces, love and strife. See also 475 bce Physics. (See essay.)

Greek philosopher Leucippus of Miletus (Turkey) [b. c. 480 bce, d. c. 425 bce] introduces the first idea of the atom, an indivisible unit of matter. See also 430 bce Physics.

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