Early Ideas and Discoveries in Astronomy

Astronomy, probably the oldest of the sciences, has origins lost in the mists or prehistory. One likely source was the land of the two rivers Tigers and Euphrates, a country we now call Iraq. There, Sumerian priests some 6,000 years ago worshipped the Sun, Moon, and “the whole host of heaven,”, and watched the sky for signs of the progress of time.

Natural Intervals of Time

In early time, no less than today, the daily course of the sun provided a natural and obvious measure of time. The Sun’s regular appearance of day and night, and its progress across the sky, associated with corresponding changes in the lengths and directions of shadows, led to the introduction of the hour. From the Sun’s motion relative to the stars came the year and the establishment of the seasons and times of seedtime and harvest. From the regular cycle of the waxing and waning of the Moon was derived the month, the basic unit of Sumerian and Babylonian calendars.

Difficulties arose when early people tried to correlate the year as determined by the Sun with the day and lunar month. As early as 2500 B.C., for example, the Egyptians adopted a solar year of 365 days, but later found that in contained more nearly 365¼ days.

Likewise the lunar month was found to contain about 29, 5 days and not a convenient 30 days. Twelve lunar months therefore totalled 354 days instead of the 365 ¼ days of the solar year. As a result all manner of ingenious devices were introduced to form a reasonably reliable calendar, but it remained a problem right up to modern times. Even today we must add an extra day to February once every four years to ensure an average year of 365 ¼ days: the calendar months are by no means equal in length: en Easter arrives sometimes in March and sometimes in April.


The Babylonians were the great star-worshippers and astrologers of antiquity. To them the heavenly bodies were gods and goddesses to whom it was necessary to pay homage. Night after night they recorded on clay tablets the position of whatever planet happened to be visible, thereby building a body of knowledge which led them to discover further regularities in the sky. After about the seventh century B.C. they were able to forecast well in advance when this or that planet would be in a particular part of the sky, or on what dates two or more planets would appear to meet. By the second century B.C. they could even predict eclipses of the moon with fair accuracy, for they discovered that eclipses which occur during a cycle of roughly 18 years repeat themselves in the subsequent cycle.

There is little doubt that astrology, or the belief that human affairs can be foretold by taking notes of events in the sky, stemmed directly from Babylonian star worship. Once established, it persisted in one form or another in several areas of scientific activity for many centuries. It certainly played an important part in astronomy, and more often than not, the two subjects were regarded as one. The association ended in the 17th century with the rapid rise of the physical sciences. Astrology had nothing to contribute to the scientific approach and therefore dropped into well-merited obscurity.


The Egyptian sky-goddess Nut, with her body arched over the Gods of Air Shu and Earth Geb