वेदों की प्राचीनता एवं काल-निर्णय / ओरायन (लोकमान्य बाल गंगाधर तिलक - खगोलीय वैदिक शोध)

28 THE ARCTIC HOME IN THE VEDAS. winter in the northern hemisphere; while when the earth is at A, the axis, retaining its direction, will be now turned towards the sun, and there will be summer in the northern hemisphere. If the axis of the earth had no motion of its own, the seasons will always occur at the same points in the orbit of the earth, as, for instance, the winter in the northern hemisphere at P and the summer at A. But this axis describes a small circle round the pole of the ecliptic in a cycle of 25,868 years, giving rise to what is called the pre- cession of the equinoxes, and consequently the inclination of the earth's axis to the plane of its orbit is not always the same at any given point in its orbit during this period. This causes the seasons to occur at different points in the earth's orbit during this great cycle. Thus if the winter in the northern hemi- sphere occurred when the earth was at P at one time, some time after it will occur at p and the succeeding points in the orbit until the end of the cycle, when it will again occur at P. The same will be the case in regard to summer at the point A and equinoxes at Q and Q'. In the diagram the dotted lines qq' and pa represent the new positions which the line QQ' and PA will assume if they revolve in the way stated above. It must also be noted that though the winter in the northern hemisphere may occur when the earth is at p instead of at P, owing to the aforesaid motion of its axis, yet the orbit of the earth and the points of perihelion and aphelion are relatively fixed and unchangeable. Therefore, if the winter in the northern hemisphere occurs at p, the earth's distance from the sun at the point will be greater than when the earth was at P. Similarly, in the course of the