10. Under the clear sky of Chaldea, India, and Egypt, cradle of the most antique civilization, one could observe the movement of the stars with as much precision as the absence of special instruments permitted. They saw at first that certain stars had a movement of their own independent of the rest, which caused them to no longer believe that they were attached to the vault. They called them wandering stars or planets, in order to distinguish them from fixed stars. They calculated their movements and periodical returns.
In the diurnal movement of the starry spheres they observed the immovableness of the polar star, around which others described, in twenty-four hours, oblique or parallel circles, smaller or greater, according to their distance from the central star. This was the first step towards the knowledge of the obliquity of the world’s axis. Moreover, long voyages enabled them to observe the change of aspect in the sky according to latitudes and seasons. The elevation of the polar star above the horizon varying with the latitude, suggested the idea of the roundness of the Earth. Thus little by little they arrived at more accurate ideas of the system of the world.
Towards the year 600 B.C., Thales of Miletus, Asia Minor, became convinced of the sphericity of the Earth, the obliquity of the ecliptic, and the cause of the eclipses.
A century later Pythagoras of Samos discovered the diurnal movement of the Earth upon its axis, its annual movement around the sun, and connected the planets and comets to the solar system.
One hundred and sixty years B.C., Hipparchus of Alexandria, Egypt, invented the astrolabe, calculated and predicted the eclipses, observed the spots on the sun, ascertained the tropical year and the duration of the revolutions of the moon.
However precious these discoveries were for the progress of science, they were nearly two thousand years in becoming popularized. These new ideas, having then as a means of diffusion only a few rare manuscripts, which remained in the possession of some philosophers who taught them to privileged disciples, the masses of the people, whom they dreamed not of enlightening, profited nothing by them, but continued to cherish old beliefs.