Day and Night

Core Idea

Day happens when your part of Earth faces the sun and receives sunlight. Night happens when your part of Earth faces away from the sun and is in darkness. This cycle of day and night repeats every 24 hours because Earth is constantly spinning (rotating). The sun does not move around the Earth -- instead, Earth spins and different parts take turns facing the sun.

How It's Best Learned

Use a globe and a flashlight in a darkened room. Shine the flashlight (sun) at the globe and slowly spin it, showing that only half the globe is lit at any time. Mark the student's home on the globe and spin to show it moving from the lit side (day) to the dark side (night). Discuss sunrise and sunset as moments when your location is moving into or out of the sunlit side.

Common Misconceptions

• The sun moves around the Earth, rising in the morning and setting at night. The sun appears to move across the sky because Earth is spinning, not because the sun is orbiting us.
• It is dark at night because the sun "turns off" or goes away. The sun is always shining -- at night, your part of Earth is just facing away from it.
• The entire world has day or night at the same time. When it is day where you are, it is night on the opposite side of the world.

Explainer

Every day, the world around you changes in a dramatic way: it goes from bright daylight to dark nighttime and back again. This happens so reliably that you probably do not think much about it. But there is an amazing reason behind it: Earth is spinning.

Imagine Earth as a ball that is slowly rotating -- spinning on an invisible pole running from the North Pole to the South Pole. It takes exactly 24 hours to complete one full spin. As it spins, different parts of Earth take turns facing the sun. When your part of Earth faces the sun, sunlight reaches you and you experience day. When Earth keeps spinning and your part faces away from the sun, the sunlight cannot reach you, and you experience night.

This means that the sun is not moving across the sky the way it appears to. It looks like the sun rises in the east, travels across the sky, and sets in the west. But what is actually happening is that Earth is spinning from west to east, making the sun appear to move in the opposite direction. It is the same illusion as looking out the window of a moving car -- the trees seem to move backward, but really you are the one moving.

Here is something to think about: when it is daytime where you live, it is nighttime on the other side of the world. Right now, as you read this in the light of day, someone on the opposite side of the planet is sleeping in darkness. And in about 12 hours, you will swap -- you will be in the dark and they will be in the sun. Earth is always half in daylight and half in shadow. The spinning just determines whose turn it is.