— Ch. 1 · Ancient Cosmological Models —
Discovery and exploration of the Solar System.
~4 min read · Ch. 1 of 6
In 560 BCE, a map of the universe drawn by Anaximander placed Earth at the center of a flat disk. Ancient civilizations from Egypt to China viewed the sky as a dome rotating above a stationary world. The Sun and Moon were immediate interests because they created day and night cycles and measured seasons. Early astronomers called planets wanderer stars due to their puzzling forward and retrograde motion against fixed background stars. Pythagorean thinkers in Greece proposed a spherical Earth during the 5th century BC. Aristotle later developed models using concentric spheres to explain planetary paths. Ptolemy published his Almagest model which remained dominant until the 16th century. This geocentric system required complex epicycles to account for observed movements. Chinese cosmology sometimes described an outer surface attached to celestial bodies or free-floating objects.
The Telescope Revolution
Galileo Galilei pointed his telescope at Jupiter in 1610 and found four satellites orbiting it. He also discovered that the Moon had craters and the Sun bore dark spots. Christiaan Huygens identified Saturn's moon Titan and the shape of its rings in 1655. Giovanni Domenico Cassini found four more moons of Saturn plus the division now named after him. Edmond Halley observed Mercury transiting the Sun in 1677 to measure distances between Earth and Venus. In 1705, Halley realized repeated comet sightings recorded the same object returning every 75 years. William Herschel discovered Uranus in 1781 while searching for binary stars in Taurus. The invention of the reflecting telescope by Isaac Newton in 1668 reduced optical errors. John W. Draper took the first astronomical photograph of the Moon in 1840 using daguerreotype technology.