Abstract

The earth, the abode of the only form of intelligent life in the universe of which we are aware, is a minor member of a system of nine planets, 40 or so moons and about 100 billion asteroids orbiting around the Sun, an average-size member of the 100-billion-star community making up our galaxy, the Milky Way. It is the third planet to the Sun, which it orbits, following an almost circular elliptical path maintaining an average distance of 1.5×108 km, with the longest and the shortest radii now being 1.53×108 km and 1.47×10 km respectively (Fig. 1). This orbit is subject to changes in its “eccentricity” (i.e., in how much it deviates from a circle) with periods of 105 and 4×10 years5 years (Fig. 2A). In addition, the elliptical orbit itself slowly rotates as shown in Fig. 2B, in what we call the precession.