Fundamentals of celestial sphere

Before one can visit the depths of astrological knowledge, one needs to be familiar with the basics. This is, however, not to be confused with the basics of astronomy that are taught in the schools. These are obviously essential. However one needs to be acquainted with larger and more generalized fundamentals of astronomy, which, although very interesting even to a moderately inquisitive mind, regrettably do not form a part of the schooling. To start with, let us understand how the celestial objects started shaping the scientific thinking of the human-being. In this philosophical approach of understanding the progress of human-thinking, one needs to start from the scratch.

Have you ever given a though to time units? How did units such as second, minute, hour, day, month, year, and, for those who don’t know yet, great year emerge? And how these units are referenced? To clarify, time without a reference, just like motion, has got no quantifiable meaning. Time-keeping was perhaps the first task which made human-beings look towards the sky. The need to keep time demanded that there be some reference. The obvious answer was the alternation of sunshine and darkness. And thus the concept of day emerged. As the human-thinking progressed, it realized that not only the day-time sun, but also the night-time stars can be used for time-referencing. In fact the star-rich night sky formed the basis of astrological conceptual development. Thus a “day” could be defined in two ways. The time required for the sun to appear at the same position after completing 1 cycle of day-night. This was known as the solar-day. Similarly the time required for a distant reference night-star to appear at the same position in a day-night cycle was known as the sidereal day. Precise observations and mathematical calculations led to conclusion that the sidereal day was shorter than the solar day, the reason for which has now become clear in modern times and is as follows.

[Wikipedia:]Solar time is measured by the apparent diurnal (daily) motion of the sun, and local noon in solar time is defined as the moment when the sun is at its highest point in the sky. The average time taken by the sun to return to its highest point is 24 hours. During the time needed by the Earth to complete a rotation around its axis (a sidereal day), the Earth moves a short distance (approximately 1°) along its orbit around the sun. Therefore, after a sidereal day, the Earth still needs to rotate a small extra angular distance before the sun reaches its highest point. A solar day is, therefore, nearly 4 minutes longer than a sidereal day. The stars, however, are so far away that the Earth's movement along its orbit makes a generally negligible difference to their apparent direction, and so they return to their highest point in a sidereal day. A sidereal day is almost 4 minutes shorter than a mean solar day.

Thus there arose mainly two systems of time-keeping: solar time and sidereal time. This has been, for years, the fundamental basis of astrological concepts and has also led to bifurcation of astrological systems between the east, predominantly India, and the West, predominantly Europe, Egypt and Israel. This will be dealt with separately in subsequent posts.