When the children all understood the way the Zodiac divides the yearly path of the earth into twelve equal parts, Betty said, “I want to know why the geography globe at school always looks just as if it was going to tip over.”
Uncle Henry laughed. “If you think the geography globe looks unsteady because its axis of iron rod is on a slant, what will you think about the earth when I tell you that it spins around in just the same slanting position, with only an imaginary line for axis?”
“Does it really?” asked Betty.
“Yes,” said Uncle Henry, “and it spins so steadily in that slanting position that the north end of its imaginary axis always points toward the same place, a point very close to the north star, or Polaris as it is called.”
“Polaris is named for the North Pole, I suppose,” said Peter.
“That’s right,” Uncle Henry replied. “Let’s get some scissors and we’ll use our big sheet of cardboard to make a cap for Paul’s head that will show you just how the slant of the earth’s axis makes it hotter in summer and colder in winter.”
“Ooh!” exclaimed Paul, “I always thought it was hot in summer because the earth got nearer to the sun then.”
“Lots of people think that, too,” said Uncle Henry, “but it isn’t so. The earth is really farther from the sun in summer.”
Betty ran for the scissors, and Uncle Henry cut out a big circle from the stiff cardboard. Then he cut out an opening in the centre of it that fitted Paul’s head just as a stiff straw hat would that was a size too big for him. The circle of cardboard dropped down until it rested on Paul’s ears and on the bridge of his nose. This cardboard brim represented the “plane of the earth’s equator,” just as the pane of glass represented the “plane of the ecliptic.” Since the “plane of the equator” is always at right angles to the slanting axis of the earth, the “plane of the equator” is always at a slant to the “plane of the ecliptic.”
If you will run a long hat-pin through an orange, and sink the orange exactly to its middle in a glass bowl filled with water, holding the hat-pin at a slant, you will see that the equator of the orange is at a slant with the surface of the water. Half of the orange’s equator curves up above the water, while half of it curves down under the water’s surface. If you fasten a cardboard ring around the orange at the equator the cardboard will then be at an angle with the surface of the water, which represents the “plane of the ecliptic.”