4. Day and night, and the seasons

The lesson, step by step

1. Get ready

   An adult pushes the skewer straight through the orange from top to bottom. Mark a dot for where you live on the upper half. Put the lamp in the middle of a table and darken the room.

   Safety: the book uses a candle. A bare lamp or an upright flashlight works just as well and is safer. If you do use a candle, an adult lights it and stays at the table.

2. Read together

   Read from the paragraph about the old-world notion that the Earth was fixed, to the end of the chapter. Two key lines:

   First: She turns round upon her axis once in every twenty-four hours.

   Secondly: She travels round the sun once in about every three hundred and sixty-five days and a quarter.

3. Day and night

   Hold the orange about a yard from the lamp. Turn it slowly on the skewer. Watch the dot go into light (morning), full light (midday), toward the shadow (evening) and into dark (night).

   SayThe lamp never moves. The turning makes the day.

   Then point to the middle of the orange and to a spot near the skewer. Say: The middle has much farther to go round in one turn. The book says a person at the equator is carried along at more than a thousand miles an hour.

4. The seasons

   Now do it the book's way. Tilt the skewer so the top points toward one wall of the room. Keep it pointing at that same wall the whole time as you walk the orange in a circle around the lamp.

   On one side, the top half gets more light: summer in the north. On the far side, the bottom half gets more: winter in the north. Halfway between, light falls evenly from pole to pole: the equinoxes.

   The book warns that everything depends on keeping the tilt pointing the same way.

5. What we know now

   The book says the Earth has a third movement and saves it for later. (At the end of Part I it tells how the Sun carries the whole family with him through space.) We now know the Sun, with all its planets, also circles the center of our Milky Way galaxy, once in about 230 million years.

   Seasons: it is still exactly the tilt, as the book shows. The Earth's distance from the Sun changes only a little through the year, and it is actually nearest in early January, during northern winter.

6. Tell it back

   Ask your child to show you, with the orange and lamp, what makes day and night, then what makes summer and winter, explaining as they go.

7. Check questions

   How long does the Earth take to turn once? To go round the Sun once?

   Is summer caused by the Earth being nearer the Sun? (Let them think about the orange.)

   What is the Sun's yearly path among the stars called?

8. Notice it this week

   At the same time each day, mark where the shadow of a fence post or a stick in the ground ends. Over weeks you will see the noon shadow grow shorter toward summer and longer toward winter.