A child on a Texas porch at sunset, one half of a globe on a table lit by a lamp beside her, the other half dark.

Day and Night

One spin about every 24 hours.

Lesson 23 of 41

Try this first

Before we start

Today’s story

Day and Night

Think of a pickup parked in a field at noon. The Sun is high and the sky is bright. Six hours later the Sun sits low and orange. Twelve hours later the stars are out.

Long ago people thought the Sun traveled around us. It is an easy thing to believe. You see it rise and you see it set. But the Sun is not what moves. The Earth is spinning like a top, very steadily.

One full spin takes about 24 hours. That is one day. Half the Earth faces the Sun at any time. Half faces away. Let us follow the spin step by step.

See it

Five steps. Every time.

Hands on

Spin the Earth

20 minutes · Do this with a grown-up nearby

You need

a ball or orange
a sticker
a lamp with no shade, or a flashlight
a dark room
a pencil

Do this

Push the pencil through the middle of the ball. This is the axis.
Stick the sticker on the ball. It is your town.
Set the lamp on a table. It is the Sun.
Hold the ball by the pencil a few steps from the lamp.
Turn the ball slowly, counterclockwise as you look down from above the pencil top.
Say out loud when the sticker has day and when it has night.

Write or draw: Draw four small circles with a lamp on the left. Shade the dark side. Mark the sticker in each one and write day or night.

Watch for: The lamp never moves, yet the sticker goes in and out of the light. Notice which edge of the ball is sunrise and which is sunset.

Safety: Ask an adult to help if you use a hot lamp bulb, and do not touch it.

Same every time

Three rules

Rule 1Earth spins and the Sun stays put.

The Sun only seems to move across the sky.

Rule 2One spin takes about 24 hours.

Day plus night make one full spin.

Rule 3When it is day here, it is night on the other side.

Earth always has a lit half and a dark half.

Grandpa Fenn’s notebook

Say it like a scientist

axis
The line Earth spins around, from pole to pole.

rotation
One full spin of an object around its axis.

day
The time when your place on Earth faces the Sun.

night
The time when your place on Earth faces away from the Sun.

Poppy’s quiz

Six questions

Tap an answer. Green means right. You will see why.

Talk about it

Say it out loud

How do you know the Sun is not moving across the sky? What could you show with a ball and a lamp?
What do you do in your town at sunrise and at sunset? What do you think a person on the far side of Earth is doing right then?

Did you know

At the equator the ground moves about 1,000 miles per hour from the spin. You do not feel it because everything moves together, smoothly.

Someone who does this

An astronomer studies the Sun, Earth and stars, and knows the spin of Earth well.

BeforeReflect, Refract, Absorb Next lessonThe Sun’s Path