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