Timothy McIrvin, age 7, of Huntsville, Alabama, for his question:

Why does the sun rise later in winter?

All through the long summer days, the sun rose early and went to bed later. When school starts in the fall, we notice that the lazy old sun comes up later in the mornings. It also sets earlier in the evenings. This makes our winter days shorter. Until around Christmas time, they get shorter and shorter and shorter. Then each morning and evening grows a tiny bit longer until the longest days of summer come around again.

From Christmas time until June, the sun rises a little earlier each morning. Through this half of the year, it also goes to bed a little later each evening. Then it changes its plans. From late June until the end of December, each day it rises later and sets earlier. From day to day, the difference is so small that we hardly notice it. Today, the sun rose just a few moments later than yesterday. Each morning lags farther behind. After a month or so, we wonder what happened to the lazy old sun.

There are two reasons why this happens. The first is the shape of the earth. As you know, our world is a big round ball. Its North Pole is exactly opposite to its South Pole. Its equator is a line around its wide waist, exactly halfway between the two opposite poles. Our half of the globe is north of the equator. South of the equator, the days grow longer while ours grow shorter.

This happens because the earth's axis is tilted. Its axis is a line from pole to pole, straight through the center of the globe. The earth spins around its axis like a top. This gives us day and night. Every 24 hours our side of the world turns to face the sun then on around to face the starry night. As it spins aratind its axis, our dizzy old globe also circles its orbit around the sun. You would expect it to march around its orbit standing straight up on its axis. But it does not.

Its axis is tilted to lean forward. During the yearly orbit, the tilted axis tips first one pole, then the other pole toward the sun. After the North Pole makes a deep bow to the sun, the South Pole makes its bow. While the North Pole bows, we see more of the sun. Our days are longer than our nights.

For us, the sun rises latest around Christmas time. This is when the South Pole makes its deepest bow. As it tips back from the sun, the days south of the equator grow shorter and our days grow longer. So, after Christmas, our sun stops rising later and starts rising a little bit earlier each morning.

If you have a model globe of the earth; you can make it spin around the axis rod through the middle. It is tilted to show how the axis leans forward as the earth goes around its orbit. This gives the North Pole a chance to bow to the sun, then the South Pole. In the fall, our sun rises later each day because the South Pole is making its bow. We see less of the sun and our days get shorter,