The beginning narrator lines are from an old RE pamphlet about springtime. It worked splendidly. Well, the answer has been given to us by astronomers, the people who study stars and planets and the ways they move through space. Astronomers have figured out the path this earth of ours takes as it spins around our sun. A year is how long it takes our earth to make one trip around the sun.
Spring begins on the day when the sun's center crosses the earth's equator.
That's an imaginary line dividing the earth into halves, north and south. On the day the sun's center crosses that dividing line, day is just exactly as long as night. Yes, but long ago, before people had learned this they did not know that spring, summer, fall and winter would keep right on happening every time our earth made a trip around the sun. They did not know there would be another spring, and another, and another, as long as the earth turns. When the cold winds tore the last leaves off the trees in fall, and winter came, with heavy snows, those people long ago were afraid.