The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for l...

Neptune is the eighth planet from the Sun and the fourth largest (by diameter). Neptune is smaller in diameter but larger in mass than Uranus. In Roman mythology Neptune (Greek: Poseidon) was the god of the Sea. After the discovery o...

Mars is the fourth planet from the Sun and the second smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is often described as the "Red Planet" because the iron oxide prevalent on its surface gives it a...

Uranus is the 7th planet from the Sun. It was discovered in 1781 by William Herschel and named for the Greek god personifying heaven. A blue-green gas giant, it has almost 15 times the mass of Earth and over 50 times its volume. It is less...

Imhotep was an Egyptian polymath who served under the Third Dynasty king Djoser as chancellor to the pharaoh and high priest of the sun god Ra (or Re) at Heliopolis. He is considered by some to be the earliest known architect and engineer a...

The Nimrud lens, also called Layard lens, is a 3000-year-old piece of rock crystal, which was unearthed in 1850 by Austen Henry Layard at the Assyrian palace of Nimrud, in modern-day Iraq. It may have been used as a magnifying glass, or as...

The zodiac is an area of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The paths of the Moon a...

Hesiod was a Greek oral poet and is often identified as the first economist. His date is uncertain but leading scholars, favor the the eighth century BC for when Hesiod lived. Since at least Herodotus's time, Hesiod and Homer have generally...

Anaximander was a pre-Socratic Greek philosopher who lived in Miletus, a city of Ionia (in modern-day Turkey). He belonged to the Milesian school and learned the teachings of his master Thales. He succeeded Thales and became the second mast...

Anaxagoras was a Pre-Socratic Greek philosopher. Born in Clazomenae in the Persian Empire (modern-day Urla, Turkey) Anaxagoras was the first to bring philosophy to Athens. According to Diogenes Laertius and Plutarch, in later life he was ch...

Empedocles was a Greek pre-Socratic philosopher and a citizen of Agrigentum, a Greek city in Sicily. Empedocles' philosophy is best known for being the origin of the cosmogenic theory of the four Classical elements. He also proposed powers...

Leucippus or Leukippos was the first Greek to develop the theory of atomism — the idea that everything is composed entirely of various imperishable, indivisible elements called atoms — which was elaborated in far greater detail by his pupil...

Democritus ("chosen of the people") was an Ancient Greek philosopher born in Abdera, Thrace, Greece. He was an influential pre-Socratic philosopher who formulated an atomic theory for the cosmos. His exact contributions are difficult to dis...

Epicurus was an ancient Greek philosopher as well as the founder of the school of philosophy called Epicureanism. Only a few fragments and letters of Epicurus's 300 written works remain. Much of what is known about Epicurean philosophy deri...

Euclid, sometimes called Euclid of Alexandria to distinguish him from Euclides of Megara, was a Greek mathematician, often referred to as the "father of geometry". He was active in Alexandria during the reign of Ptolemy I (323–283 BC). His...