History of astronomy


The history of astronomy focuses on the efforts of civilizations to understand the universe beyond earth's atmosphere. Astronomy is one of the oldest natural sciences, achieving a high level of success in the second half of the first millennium. Astronomy has origins in the religious, mythological, cosmological, calendrical, and astrological beliefs and practices of prehistory. Early astronomical records date back to the Babylonians around 1000 BC. There is also astronomical evidence of interest from early Chinese, Central American and North European cultures.
Astronomy was used by early cultures for timekeeping, navigation, spiritual and religious practices, and agricultural planning. Ancient astronomers observed and charted the skies in an effort to learn about the workings of the universe. During the Renaissance Period, revolutionary ideas emerged about astronomy. One such idea was contributed in 1543 by Polish astronomer Nicolaus Copernicus, who developed a heliocentric model that depicted the planets orbiting the Sun. This was the start of the Copernican Revolution, with the invention of the telescope in 1608 playing a key part. Later developments included the reflecting telescope, astronomical photography, astronomical spectroscopy, radio telescopes, cosmic ray astronomy, infrared telescopes, space telescopes, ultraviolet astronomy, X-ray astronomy, gamma-ray astronomy, space probes, neutrino astronomy, and gravitational-wave astronomy.
The success of astronomy, compared to other sciences, was achieved for several reasons. Astronomy was the first science to have a mathematical foundation. Standardized measuring instruments such as armillary spheres and quadrants provided a solid base for collecting, verifying and communicating data. Throughout the years, astronomy has broadened into multiple subfields such as astrophysics, observational astronomy, theoretical astronomy, and astrobiology.

Early history

Early cultures identified celestial objects with gods and spirits. They related these objects to phenomena such as rain, drought, seasons, and tides. It is generally believed that the first astronomers were priests who believed celestial objects and events to be manifestations of the divine, hence the connection to what is now called astrology. A 32,500-year-old carved ivory mammoth tusk could contain the oldest known star chart. It has also been suggested that drawings on the wall of the Lascaux caves in France dating from 33,000 to 10,000 years ago could be a graphical representation of the Pleiades, the Summer Triangle, and the Northern Crown. Ancient structures with possibly astronomical alignments probably fulfilled astronomical, religious, and social functions.
Calendars of the world have often been set by observations of the Sun and Moon and were important to agricultural societies, in which the harvest depended on planting at the correct time of year. The nearly full moon was also the only lighting for night-time travel into city markets.
The common modern calendar is based on the Roman calendar. Although originally a lunar calendar, it broke the traditional link of the month to the phases of the Moon and divided the year into twelve almost-equal months, that mostly alternated between thirty and thirty-one days. Julius Caesar instigated calendar reform in 46 BC and introduced what is now called the Julian calendar, based upon the day year length originally proposed by the 4th century BC Greek astronomer Callippus.

Prehistoric Europe

Ancient astronomical artifacts have been found throughout Europe. The artifacts demonstrate that Neolithic and Bronze Age Europeans had a sophisticated knowledge of mathematics and astronomy.
Among the discoveries are:
  • Paleolithic archaeologist Alexander Marshack put forward a theory in 1972 that bone sticks from locations like Africa and Europe from possibly as long ago as 35,000 BC could be marked in ways that tracked the Moon's phases, an interpretation that has met with criticism.
  • The Warren Field calendar in the Dee River valley of Scotland's Aberdeenshire was first excavated in 2004 but was revealed in 2013 as a find of huge significance. It is to date the oldest known calendar, created around 8,000 BC and predating all other calendars by some 5,000 years. The calendar takes the form of an early Mesolithic monument containing a series of 12 pits which appear to help the observer track lunar months by mimicking the phases of the Moon. It also aligns to sunrise at the winter solstice, thus coordinating the solar year with the lunar cycles. The monument had been maintained and periodically reshaped, perhaps up to hundreds of times, in response to shifting solar/lunar cycles, over the course of 6,000 years, until the calendar fell out of use around 4,000 years ago.
  • Goseck circle is located in Germany and belongs to the linear pottery culture. First discovered in 1991, its significance was only clear after results from archaeological digs became available in 2004. The site is one of hundreds of similar circular enclosures built in a region encompassing Austria, Germany, and the Czech Republic during a 200-year period starting shortly after 5000 BC.
  • The Nebra sky disc is a Bronze Age bronze disc that was buried in Germany, not far from the Goseck circle, around 1600 BC. It measures about diameter with a mass of and displays a blue-green patina inlaid with gold symbols. Found by archeological thieves in 1999 and recovered in Switzerland in 2002, it was soon recognized as a spectacular discovery, among the most important of the 20th century. Investigations revealed that the object had been in use around 400 years before burial, but that its use had been forgotten by the time of burial. The inlaid gold depicted the full moon, a crescent moon about 4 or 5 days old, and the Pleiades star cluster in a specific arrangement, forming the earliest known depiction of celestial phenomena. Twelve lunar months pass in 354 days, requiring a calendar to insert a leap month every two or three years in order to keep synchronized with the solar year's seasons. The earliest known descriptions of this coordination were recorded by the Babylonians in the sixth or seventh centuries BC, over one thousand years later. Those descriptions verified ancient knowledge of the Nebra sky disc's celestial depiction as the precise arrangement needed to judge when to insert the intercalary month into a lunisolar calendar, making it an astronomical clock for regulating such a calendar a thousand or more years before any other known method.
  • The Kokino site, discovered in 2001, sits atop an extinct volcanic cone at an elevation of, occupying about 0.5 hectares overlooking the surrounding countryside in North Macedonia. A Bronze Age astronomical observatory was constructed there around 1900 BC and continuously served the nearby community that lived there until about 700 BC. The central space was used to observe the rising of the Sun and full moon. Three markings locate sunrise at the summer and winter solstices and at the two equinoxes. Four more give the minimum and maximum declinations of the full moon: in summer, and in winter. Two measure the lengths of lunar months. Together, they reconcile solar and lunar cycles in marking the 235 lunations that occur during 19 solar years, regulating a lunar calendar. On a platform separate from the central space, at lower elevation, four stone seats were made in north–south alignment, together with a trench marker cut in the eastern wall. This marker allows the rising Sun's light to fall on only the second throne, at midsummer. It was used for ritual ceremony linking the ruler to the local sun god, and also marked the end of the growing season and time for harvest.
  • Golden hats of Germany, France and Switzerland dating from 1400 to 800 BC are associated with the Bronze Age Urnfield culture. The Golden hats are decorated with a spiral motif of the Sun and the Moon. They were probably a kind of calendar used to calibrate between the lunar and solar calendars. Modern scholarship has demonstrated that the ornamentation of the gold leaf cones of the Schifferstadt type, to which the Berlin Gold Hat example belongs, represent systematic sequences in terms of number and types of ornaments per band. A detailed study of the Berlin example, which is the only fully preserved one, showed that the symbols probably represent a lunisolar calendar. The object would have permitted the determination of dates or periods in both lunar and solar calendars.

    Ancient times

Mesopotamia

The origins of astronomy can be found in Mesopotamia, the "land between the rivers" Tigris and Euphrates, where the ancient kingdoms of Sumer, Assyria, and Babylonia were located. A form of writing known as cuneiform emerged among the Sumerians around 3500–3000 BC. Our knowledge of Sumerian astronomy is indirect, via the earliest Babylonian star catalogues dating from about 1200 BC. The fact that many star names appear in Sumerian suggests a continuity reaching into the Early Bronze Age. Astral theology, which gave planetary gods an important role in Mesopotamian mythology and religion, began with the Sumerians. They also used a sexagesimal place-value number system, which simplified the task of recording very large and very small numbers. The modern practice of dividing a circle into 360 degrees, or an hour into 60 minutes, began with the Sumerians. For more information, see the articles on Babylonian numerals and mathematics.
Mesopotamia is worldwide the place of the earliest known astronomer and poet by name: Enheduanna, Akkadian high priestess to the lunar deity Nanna/Sin and princess, daughter of Sargon the Great. She had the Moon tracked in her chambers and wrote poems about her divine Moon.
Classical sources frequently use the term Chaldeans for the astronomers of Mesopotamia, who were originally a people, before being identified with priest-scribes specializing in astrology and other forms of divination.
The first evidence of recognition that astronomical phenomena are periodic and of the application of mathematics to their prediction is Babylonian. Tablets dating back to the Old Babylonian period document the application of mathematics to the variation in the length of daylight over a solar year. Centuries of Babylonian observations of celestial phenomena are recorded in the series of cuneiform tablets known as the Enūma Anu Enlil. The oldest significant astronomical text that we possess is Tablet 63 of the Enūma Anu Enlil, the Venus tablet of Ammi-saduqa, which lists the first and last visible risings of Venus over a period of about 21 years and is the earliest evidence that the phenomena of a planet were recognized as periodic. The MUL.APIN contains catalogues of stars and constellations as well as schemes for predicting heliacal risings and the settings of the planets, lengths of daylight measured by a water clock, gnomon, shadows, and intercalations. The Babylonian GU text arranges stars in 'strings' that lie along declination circles and thus measure right-ascensions or time-intervals, and also employs the stars of the zenith, which are also separated by given right-ascensional differences.
A significant increase in the quality and frequency of Babylonian observations appeared during the reign of Nabonassar. The systematic records of ominous phenomena in Babylonian astronomical diaries that began at this time allowed for the discovery of a repeating 18-year cycle of lunar eclipses, for example. The Greek astronomer Ptolemy later used Nabonassar's reign to fix the beginning of an era, since he felt that the earliest usable observations began at this time.
The last stages in the development of Babylonian astronomy took place during the time of the Seleucid Empire. In the 3rd century BC, astronomers began to use "goal-year texts" to predict the motions of the planets. These texts compiled records of past observations to find repeating occurrences of ominous phenomena for each planet. About the same time, or shortly afterwards, astronomers created mathematical models that allowed them to predict these phenomena directly, without consulting records. A notable Babylonian astronomer from this time was Seleucus of Seleucia, who was a supporter of the heliocentric model.
Babylonian astronomy was the basis for much of what was done in Greek and Hellenistic astronomy, in classical Indian astronomy, in Sassanian Iran, in Byzantium, in Syria, in Islamic astronomy, in Central Asia, and in Western Europe.