Early
cultures identified celestial objects with
gods and spirits. They related these objects (and their movements) 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.
Calendars of the world have often been set by observations of the Sun and Moon (marking the
day,
month, and
year) 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.
Mesopotamia recording
Halley's Comet in 164 BC 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 (base 60) 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 ( – BCE). 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 (747–733 BC). 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 (323–60 BC). 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.
India Astronomy in the Indian subcontinent dates back to the period of
Indus Valley Civilisation during 3rd millennium BC, when it was used to create calendars. As the Indus Valley Civilization did not leave behind written documents, the oldest extant Indian astronomical text is the
Vedanga Jyotisha, dating from the
Vedic period. The Vedanga Jyotisha is attributed to Lagadha and has an internal date of approximately 1350 BC, and describes rules for tracking the motions of the Sun and the Moon for the purposes of ritual. It is available in two recensions, one belonging to the Rig Veda, and the other to the Yajur Veda. According to the Vedanga Jyotisha, in a
yuga or "era", there are 5 solar years, 67 lunar sidereal cycles, 1,830 days, 1,835 sidereal days, and 62 synodic months. During the sixth century, astronomy was influenced by the Greek and Byzantine astronomical traditions.
Aryabhata (476–550), in his magnum opus
Aryabhatiya (499), propounded a computational system based on a planetary model in which the Earth was taken to be
spinning on its axis and the periods of the planets were given with respect to the Sun. He accurately calculated many astronomical constants, such as the periods of the planets, times of the
solar and
lunar eclipses, and the instantaneous motion of the Moon. Early followers of Aryabhata's model included
Varāhamihira,
Brahmagupta, and
Bhāskara II. Astronomy was advanced during the
Shunga Empire, and many
star catalogues were produced during this time. The Shunga period is known as the "Golden age of astronomy in India". It saw the development of calculations for the motions and places of various planets, their rising and setting,
conjunctions, and the calculation of eclipses. By the sixth century, Indian astronomers believed that comets were celestial bodies that re-appeared periodically. This was the view expressed in the sixth century by the astronomers
Varahamihira and Bhadrabahu. The tenth-century astronomer
Bhattotpala listed the names and estimated periods of certain comets, but it is not known how these figures were calculated or how accurate they were.
Greece and Hellenistic world was an
analog computer dating from between 200 BC to 80 BC designed to calculate the positions of astronomical objects. The
Ancient Greeks developed astronomy, which they treated as a branch of mathematics, to a highly sophisticated level. The first geometrical, three-dimensional models to explain the apparent motion of the planets were developed in the 4th century BC by
Eudoxus of Cnidus and
Callippus of Cyzicus. Their models were based on nested homocentric spheres centered upon the Earth. Their younger contemporary
Heraclides Ponticus proposed that the Earth rotates around its axis. A different approach to celestial phenomena was taken by natural philosophers such as
Plato and
Aristotle. They were less concerned with developing mathematical predictive models than with developing an explanation of the reasons for the motions of the Cosmos. In his
Timaeus, Plato described the universe as a spherical body divided into circles carrying the planets and governed according to harmonic intervals by a
world soul. Aristotle, drawing on the mathematical model of Eudoxus, proposed that the universe was made of a complex system of concentric
spheres, whose circular motions combined to carry the planets around the Earth. This basic cosmological model prevailed, in various forms, until the 16th century. In the 3rd century BC
Aristarchus of Samos was the first to suggest a
heliocentric system, although only fragmentary descriptions of his idea survive. Greek geometrical astronomy developed away from the model of concentric spheres to employ more complex models in which an
eccentric circle would carry around a smaller circle, called an
epicycle which in turn carried around a planet. The first such model is attributed to
Apollonius of Perga and further developments in it were carried out in the 2nd century BC by
Hipparchus of Nicea. Hipparchus made a number of other contributions, including the first measurement of
precession and the compilation of the first star catalog in which he proposed our modern system of
apparent magnitudes. The
Antikythera mechanism, an
ancient Greek astronomical observational device for calculating the movements of the Sun and the Moon, possibly the planets, dates from about 150–100 BC, and was the first ancestor of an astronomical
computer. It was discovered in an ancient shipwreck off the Greek island of
Antikythera, between
Kythera and
Crete. The device became famous for its use of a
differential gear, previously believed to have been invented in the 16th century, and the miniaturization and complexity of its parts, comparable to a clock made in the 18th century. The original mechanism is displayed in the Bronze collection of the
National Archaeological Museum of Athens, accompanied by a replica.
Ptolemaic system Depending on the historian's viewpoint, the acme or corruption of Classical physical astronomy is seen with
Ptolemy, a Greco-Roman astronomer from Alexandria of Egypt, who wrote the classic comprehensive presentation of geocentric astronomy, the
Megale Syntaxis (Great Synthesis), better known by its Arabic title
Almagest, which had a lasting effect on astronomy up to the
Renaissance. In his
Planetary Hypotheses, Ptolemy ventured into the realm of cosmology, developing a physical model of his geometric system, in a universe many times smaller than the more realistic conception of
Aristarchus of Samos four centuries earlier.
Egypt , constructed by Neolithic populations, located in
Aswan,
Upper Egypt. Excavations of the megalith structures were completed in 2008. (circa 1479–1458 BC), depicting constellations, protective deities, and twenty-four segmented wheels for the hours of the day and the months of the year Megalithic structures located in
Nabta Playa, Upper Egypt featured astronomy, calendar arrangements in alignment with the heliacal rising of
Sirius and supported calibration the yearly calendar for the annual Nile flood. These practices have been linked with the emergence of
cosmology in Old Kingdom Egypt. The precise orientation of the
Egyptian pyramids affords a lasting demonstration of the high degree of technical skill in watching the heavens attained in the 3rd millennium BC. It has been shown the Pyramids were aligned towards the
pole star, which, because of the
precession of the equinoxes, was at that time
Thuban, a faint star in the constellation of
Draco. Evaluation of the site of the temple of
Amun-Re at
Karnak, taking into account the change over time of the
obliquity of the ecliptic, has shown that the Great Temple was aligned on the rising of the
midwinter Sun. The length of the corridor down which sunlight would travel would have limited illumination at other times of the year. The Egyptians also found the position of Sirius (the dog star), who they believed was Anubis, their jackal-headed god, moving through the heavens. Its position was critical to their civilisation as when it rose heliacal in the east before sunrise it foretold the flooding of the Nile. It is also the origin of the phrase "dog days of summer". Astronomy played a considerable part in
religious matters for fixing the dates of festivals and determining the hours of the
night. The titles of several temple books are preserved recording the movements and phases of the
Sun,
Moon, and
stars. The rising of
Sirius (
Egyptian: Sopdet,
Greek: Sothis) at the beginning of the inundation was a particularly important point to fix in the yearly calendar. Writing in the
Roman era,
Clement of Alexandria gives some idea of the importance of astronomical observations to the sacred rites: And after the Singer advances the Astrologer (ὡροσκόπος), with a
horologium (ὡρολόγιον) in his hand, and a
palm (φοίνιξ), the symbols of
astrology. He must know by heart the
Hermetic astrological books, which are four in number. Of these, one is about the arrangement of the fixed stars that are visible; one on the positions of the Sun and Moon and five planets; one on the conjunctions and phases of the Sun and Moon; and one concerns their risings. The Astrologer's instruments (
horologium and
palm) are a
plumb line and sighting instrument. They have been identified with two inscribed objects in the
Berlin Museum; a short handle from which a plumb line was hung, and a palm branch with a sight-slit in the broader end. The latter was held close to the eye, the former in the other hand, perhaps at arm's length. The "Hermetic" books which Clement refers to are the Egyptian theological texts, which probably have nothing to do with
Hellenistic Hermetism. From the tables of stars on the ceiling of the tombs of
Rameses VI and
Rameses IX it seems that for fixing the hours of the night a man seated on the ground faced the Astrologer in such a position that the line of observation of the
pole star passed over the middle of his head. On the different days of the year each hour was determined by a fixed star
culminating or nearly culminating in it, and the position of these stars at the time is given in the tables as in the centre, on the left eye, on the right shoulder, etc. According to the texts, in founding or rebuilding temples the
north axis was determined by the same apparatus, and we may conclude that it was the usual one for astronomical observations. In careful hands it might give results of a high degree of accuracy.
China star map of
Su Song (1020–1101) showing the south polar projection The astronomy of
East Asia began in
China.
Solar term was completed in
Warring States period. The knowledge of Chinese astronomy was introduced into East Asia. Astronomy in China has a long history. Detailed records of astronomical observations were kept from about the 6th century BC, until the introduction of Western astronomy and the telescope in the 17th century. Chinese astronomers were able to precisely predict eclipses. Much of early Chinese astronomy was for the purpose of timekeeping. The Chinese used a lunisolar calendar, but because the cycles of the Sun and the Moon are different, astronomers often prepared new calendars and made observations for that purpose. Astrological divination was also an important part of astronomy. Astronomers took careful note of
"guest stars" () which suddenly appeared among the
fixed stars. They were the first to record a supernova, in the Astrological Annals of the Houhanshu in 185 AD. Also, the supernova that created the
Crab Nebula in 1054 is an example of a "guest star" observed by Chinese astronomers, although it was not recorded by their European contemporaries. Ancient astronomical records of phenomena like supernovae and comets are sometimes used in modern astronomical studies. The world's first
star catalogue was made by
Gan De, a
Chinese astronomer, in the 4th century BC.
Mesoamerica ,
Mexico Maya astronomical
codices include detailed tables for calculating
phases of the Moon, the recurrence of eclipses, and the appearance and disappearance of
Venus as morning and
evening star. The Maya based their
calendrics in the carefully calculated cycles of the
Pleiades, the
Sun, the
Moon,
Venus,
Jupiter,
Saturn,
Mars, and also they had a precise description of the eclipses as depicted in the
Dresden Codex, as well as the ecliptic or zodiac, and the
Milky Way was crucial in their Cosmology. A number of important Maya structures are believed to have been oriented toward the extreme risings and settings of Venus. To the ancient Maya, Venus was the patron of war and many recorded battles are believed to have been timed to the motions of this planet. Mars is also mentioned in preserved astronomical codices and early
mythology. Although the
Maya calendar was not tied to the Sun,
John Teeple has proposed that the Maya calculated the
solar year to somewhat greater accuracy than the
Gregorian calendar. ==Middle Ages==