There are no written records to tell us who the first astronomers were, but one feels instinctively that, with the first stirrings of intelligence, Man's gaze must have turned heavenwards. The regular rising and setting of the Sun and the waxing and waning of the Moon provided a method for measuring the passage of time and for predicting the changing of the seasons. Stonehenge is but one example of astronomical calendars built by ancient civilisations in the hope of understanding the workings of the universe. The earliest records from civilisations in Babylonia, China, India and South America indicate a preoccupation with lunar phases and other cycles, such as the appearance and disappearance of the planet Venus, which would lead to the development of a dependable calendar.
Egyptian Astronomy
Egyptian astronomers had fairly accurate calendars as far back as 3000 BC. They had already divided the year into 365 days with 12 'months' of 30 days each; the extra five days were declared 'feast days' and added on at the end of the year - a tradition which survives today in the form of 'end-of-year' celebrations. Each month was divided into three decades of ten days each, which corresponded with the rising of certain groups of stars, the 'decans', 36 of which, with a bit of fudging by the astronomers, marked the passage of the year by dividing the sky into equal 10-degree steps. In addition, the 'hours' of the night were also governed by the rising of the same decans. Originally, the length of these hours varied in duration from one time of year to another; the Egyptians calibrated their calendar at the time of the summer solstice, when nights are shortest and only 12 decans appear. Later, hours of equal duration were introduced and a symmetrical set of 12 daytime hours, including morning and evening twilight, was introduced giving the 24-hour day which we still use. Julius Caesar appointed Sosigenes, an Egyptian astronomer from Alexandria, to convert Rome to the solar civil calendar, rather than one based on the phases of the Moon which was difficult to keep in step with the seasons.
Having established a calendar, the value of which would be recognised as the standard reference system by astronomers throughout the Middle Ages, the Egyptians ceased their wonderings about the heavens and concentrated instead on observations of the star Sirius. When, after 70 days of invisibility, the brightest star in the sky reappeared just before the Sun at dawn around the time of the summer solstice, the so-called heliacal rising, it heralded the approach of the Nile flood, so vital to Egyptian agriculture. The time was kept by means of sundials during the day and by water clocks ( clepshydra ) at night - the rising and setting of the decans had more significance to the passage of the souls of the dead through the underworld and so became the realm of priests and mystics.
Babylonian Astronomy
While Egyptian astronomy made little advancement after the second millenium BC, the developing civilisation in Mesopotamia made significant contributions to astronomical knowledge. The world's first known city states developed between 4000 BC and 3000 BC in the southern part of the floodplain between the Tigris and Euphrates rivers in what is now Iraq. The southernmost part was the ancient land of Sumer where food surpluses generated by the fertile soils led to the emergence of social classes which included craftsmen, merchants and administrators.The Sumerians date from the fourth millenium BC until the fall of Ur in 2006 BC when the Babylonians took over the region. In addition to their invention of the wheel, the Sumerians, and later the Babylonians, who inherited their knowledge and culture, had a fascination with astronomy and astrology. They pursued astronomy, not simply for its practical uses in establishing the calendar, but to acquire knowledge for its own sake.They are perhaps justifiably regarded as having founded astronomy as a science.
Fortunately for historians, the Sumerians developed a system of writing, known as cuneiform, using a reed stylus to make wedge-shaped symbols on clay tablets which were then baked in the heat of the Sun's rays. In this way, their earliest astronomical records have been preserved and, although only deciphered for the first time in the 1880s, we find evidence of their observations of Venus and of eclipses. They had a 360-day calendar and a lunar month of 29 ½ days ( rather than 30 ) and they had to add an additional month every few years to account for the fact that the year is nearer to 365.25 days ( actually it is 365.2422 days in length and the numerous attempts to fit this to an accurate calendar would fill a book by themselves - for example see Julius Caesar). The Babylonians, using the same numerical system as the conquered Sumerians, developed a mathematical theory of lunar motion and they knew and named the known planets ( Mercury,Venus,Mars,Jupiter and Saturn, as well as the Sun and Moon ) and the constellations which make up the Zodiac.
The Babylonians were not however particularly keen on observational astronomy but rather, they were preoccupied with fitting known phenomena to mathematical equations. They used a 'base-60' ( sexagesimal ) counting system which led them to divide the circle into 360 degrees and parts of an hour likewise. They did however settle for a seven-day week, perhaps because like the Egyptians, they believed that each of the seven 'planets' was the 'ruler' of a particular day ( the names of the days of the week in European languages still reflect this notion - Sonntag, Montag or lunedi, martedi,mercoledi,giovedi,venerdi,Saturday ). Their main effort was directed towards predicting the recurrence of certain astronomically significant events such as eclipses. Many of their ideas were influenced by the Chaldeans who invaded Babylonia from the south in the 11th century BC. They are remembered more as astrologers than astronomers; they were zealous sky-worshippers and skilful magicians. Important events on the earth were correlated with celestial phenomena, together with 'omens' obtained from other sources such as by studying the organs of sacrificial animals. The foundations of medieval 'magic' and astrology were laid down around 1000 BC.
The civilisation which began to flourish in the Aegean around 2500BC, overlapped with those of the Sumerians and Egyptians and gave rise to the first philosophers of Nature, who formed their own ideas and devised interpretations which, handed down over the centuries, were to form the basis of western scientific thought for over 2000 years.Much of the knowledge of the Babylonians was passed on to the Greeks by the teachings of Berossos, who moved to the Greek island of Cos about 270 BC. One of the main reasons for the transmission of astronomical knowledge was probably a widespread belief in astrology as the 'science' which gave insight into the causes of events on earth. It is not true however that astronomy originated from astrology - rather it was the other way around. Nor is it entirely correct to regard astrology as pure nonsense - it was based on careful observations, although its deductions may have been flawed and influenced by civil events and a desire to appear knowledgable or powerful in front of despotic rulers who demanded accurate forecasts of the outcome of battles on pain of immediate execution.It stands in sharp contrast to the ideas of arbitrary rulership by deities or the possibility of influencing events by magical operations. Compared to religion, magic and mysticism, astrology was almost pure science. It is largely due to the Greek influence that astrology survives today in its present form, and it is entirely due to the influence of Greek philosophy and its interpretation by the Medieval world that the progress of science was effectively halted for most of the last two millenia.