The vernal equinox occurs in March and officially marks the first day of spring in the Northern Hemisphere. We can thank the sun, the earth, and a little geometry for this annual astronomical event!
Our seasons are caused by the tilt of the earth on its axis. The northern hemisphere tilts away from the sun in the winter and toward the sun in the summer. The sun strikes the equator directly only twice a year – on the vernal and autumnal equinoxes. On those two days, day and night are of equal length. Without the earth’s tilt on its axis, we would not have seasons and the number of hours of daylight would always be the same.
The Desana and Barasana Indians of the Amazon basin have been keen observers of relationships between the earth and the sky. According to their creation myths, on the “First Day” the Sun Father fertilized the world at its center (the equator) and the first people emerged from this place. It is believed that equinoxes are days of renewal; when the sun is directly overhead, the sun’s rays penetrate the earth and make the world fertile again.
Suppose the Indian legends taught us that 1/4 of the sun’s rays reflected to the east when they struck the earth, 1/3 of the rays reflected to the west, and the rest penetrated the earth to create the first people. What fraction of the sun’s rays penetrated the earth?