The Zodiac

The Zodiac system was principally developed to facilitate easier time-keeping through the course of a year. Based on observations, 12 constellations that were most apt in terms of fixed position, brightness, ease of recognition, uniformity of spacing on the celestial sphere (refer fig. 2) etc. were identified and anthropomorphized i.e. personified. The number 12 was perhaps chosen due to simplicity in specific-constellation identification on the celestial sphere of 360˚ (360˚/12=30˚) and in time-keeping over suitably smaller and uniform periods. The Zodiac basically served as means of distinguishing the further smaller parts of a year, and thus the concept of month originated. The personification was done on the basis of the shape of the constellation, for ex: Pisces (2 Fish), Taurus (Bull) etc. or on the basis of the events of nature occurring during that part of year, for ex: Aquarius: The pitcher-bearer which marked the beginning of the spring. Here it is important to note that the events of nature do not form an absolute reference to denote a constellation, because the same keep on shifting in the course of year, as shall be shown when dealing with the phenomenon “Precession of equinoxes”. Because the zodiac was perhaps developed at a time when Aquarius, more or less, marked the beginning of the spring, this association of the constellation to the beginning of the spring was valid in those times.

The Seasons

The most obvious means of time-keeping over longer spans were the natural seasons. Cultures dating back as far as thousands of years BC were aware of the cyclic seasons, which are named as Spring, Summer, Autumn and Winter. Now, in modern times, we know the precise reason of the occurrence of seasons. In ancient times however, seasons formed the basis of time-keeping. From precise observations and mathematical calculations it was noted that the days and nights were unequal in the course of entire cycle. There were two days in the cycle on which day and night were of almost equal duration. These were known as equinoxes and they marked the peak of the seasons: spring and autumn. Likewise the day of maximum daytime marked summer, whereas the day of maximum night-time marked winter. This cycle was referred to as a year and, when quantized in the unit of “day” (solar/sidereal), was roughly equal to 365 days.