Astronomy began with farming calendars and still welcomes amateurs to discover comets
Few sciences let hobbyists make real discoveries, but astronomy does; amateurs with backyard telescopes still find new comets. That openness fits a field born from practical needs. Long before physics, people aligned stones with rising stars so they could tell when to plant or when the Nile would flood.
Evidence of early skywatching is everywhere. Stonehenge hints at it, and the Nebra sky disc bears symbols read as a sun, a moon and a cluster of seven stars. At Nabta Playa in Upper Egypt, megaliths lined up with the dawn rising of Sirius, helping calibrate the calendar for the yearly flood. The Babylonians turned observation into mathematics, discovering that lunar eclipses repeat in a cycle of 223 lunar months.
Greek thinkers pushed toward physical explanations. Heracleides Ponticus proposed in the fourth century BC that Earth spins on its axis, and Aristarchus of Samos suggested a century later that Earth and the planets circle the Sun. Yet Ptolemy's Earth-centred system, set out in the Almagest, dominated for over a thousand years because it predicted positions better than anything else then available. Scholars in the Islamic world built observatories by the early ninth century; al-Sufi described the Andromeda Galaxy in 964, and the brilliant supernova of 1006 was recorded in both Egypt and China. For some six centuries the Catholic Church funded astronomy more than probably any other institution, partly to fix the date of Easter.
Copernicus revived the Sun-centred model, and around 1610 Galileo, using the newly invented telescope, saw phases of Venus and found that the Milky Way is made of countless stars. Kepler, working from two decades of Tycho Brahe's measurements, described elliptical orbits; Newton's gravitation finally explained them. William Herschel found Uranus in 1781, the first new planet discovered.
Spectroscopy then opened the stars' chemistry. Joseph von Fraunhofer counted some 574 dark lines in sunlight in 1814 and 1815, and in 1859 Gustav Kirchhoff tied them to specific elements. Despite a shared origin, astronomy parted ways with astrology because physics backs one and not the other.
Source: Astronomy
