Abstract
It is generally accepted that the angle of the earth's tilt, called the obliquity of the ecliptic, varies between 22 and 24.5 degrees due to the pull of the moon, sun and planets on the bulge at the earth's equator. This angle of tilt changes very slowly, having a cycle of approximately 40,000 years (see Figure 2). The mathematical analysis of this variation of the tilt was carried out by Stockwell, whose formula was further refined by Newcomb.