Billy Rose, age 8, of Charlotte, North Carolina, for his question:

Why doesn't the North Star move?

Our merry old world spins around and around like a dizzy dancer. If it stopped to rest for a while, the sun would stand still    and all the stars would stop moving over the sky. Every star would stay in its fixed place, just as the North Star does. Actually, they don't really move over our sky. They just seem to move because our dizzy earth spins around. And it happens to spin so that the North Star gets left out of the starry parade.

A big thing is easier to understand when we compare it.with something small. Polaris, the North Star, happens to be enormous. It is really two stars, bigger than our sun. It is so far away that a fast spaceship would take hundreds of years to reach it. Such big things are hard to understand. It is even hard for our minds to grasp the big round size of our earth. Things get even harder when we try to imagine how our globe spins around like a top.

So let's begin with something smaller, say about the size of an eight year old boy. You are just the one to start probing the big mystery. Find a spot or marker of some sort on the ceiling. The light fixture will do nicely. Now lift your arm and point to the place you chose on the ceiling. Keeping pointing, but shift your feet so that you turn around, right where you stand. Keep pointing while you figure out what happened. Your chest turned around to face each side of the moon, one by one. So did your back. But while the rest of you turned around, your finger kept pointing to the same old spot on the ceiling.

Now you can change that simple little test into something big. Pretend that your body was the huge, spinning earth. It spins around its axis. The axis is a long line from pole to pole, straight through the middle of the globe. One end of it is the North Pole, the other end is the South Pole. The axis does not spin around with the rest of the globe. The North Pole keeps its finger pointed up to the same spot, where Polaris shines in the sky. The South Pole keeps pointing out in the opposite direction. Though there is no South Pole star to mark the spot.

We look up and see the stars like a field of shining flowers. But the spinning earth moves us around to face the next and the next view of the sky. As the scene changes, the stars seem to parade overhead. Only Polaris the North Star stays in the same place. This is because the North Pole points to the same spot, while our part of the world spins around with the globe.

Polaris stays put if we stay put. At the North Pole it stays at the top of the sky. As we go south, it sinks lower. Let's imagine a model sky, like an upside down bowl. Its highest point is overhead, its rim rests on the ground around the horizon. Let's pretend it measures 90 inches from the horizon right up to the top. Now suppose we travel south to North Carolina. In our model sky, the North Star would be 35 inches above the horizon    and 55 inches lower than it was at the North Pole.