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...

Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of icy trans-Neptunian objects. It was the first such object to be discovered. It is the largest and second-most massive known dwarf planet in the S...

Venus is the second planet from the Sun and the sixth largest. On June 8 2004, Venus will pass directly between the Earth and the Sun, appearing as a large black dot travelling across the Sun's disk. This event is known as a "transit of Ve...

Pangaea or Pangea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It formed approximately 300 million years ago and then began to break apart after about 100 million years. Unlike the present Earth, much...

Thera, or the modern island of Santorini, located sixty-nine miles north of the island of Crete in the Aegean Sea, was devastated by a volcanic eruption sometime in the 15th century BC. The eruption was one the the most powerful in the past...

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...

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...

Pytheas was a Greek merchant, geographer and explorer from the Greek colony Massilia (today Marseille). He made a voyage of exploration to northwestern Europe around 325 BC. He probably travelled around a considerable part of Great Britain,...

Eratosthenes of Cyrene was a Greek mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. He invented the discipline of geography, including the...

Hipparchus was the most important Greek astronomers of his time. He very accurately cataloged over 1,000 stars and invented the mathematical science of trigonometry. Ptolemy was a great admirer of Hipparchus's research and recorded some of...

Posidonius of Apameia or of Rhodes was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria. He was acclaimed as the greatest polymath of his age. None of his vast body of work can be...

Strabo was a Greek historian, geographer and philosopher. Strabo is mostly famous for his 17-volume work Geographica, which presented a descriptive history of people and places from different regions of the world known to his era. Although...

Zhang Heng was a Chinese astronomer, mathematician, inventor, geographer, cartographer, artist, poet, statesman, and literary scholar from Nanyang, Henan. He lived during the Eastern Han Dynasty (AD 25–220) of China. He was educated in the...

Claudius Ptolemy was a Greco-Egyptian writer of Alexandria, known as a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in the city of Alexandria in the Roman province of Egypt...

Pausanias was a Greek traveler and geographer of the 2nd century AD, who lived in the times of Hadrian, Antoninus Pius and Marcus Aurelius. He is famous for his Description of Greece, a lengthy work that describes ancient Greece from firsth...