Why do we have day and night?
The Sun always lights half of Earth. Earth spins, so each place takes turns facing the Sun (day) and facing away (night).
Daytime
India is on the side of Earth that faces the Sun, so it gets sunlight.
Earth is shown at the time of year when day and night are about equal (March or September). Sizes and distances are not to scale.
Day and night: questions and answers
We have day and night because Earth spins. The Sun lights up the half of Earth that faces it. As Earth turns, your home moves into the sunlight (day) and then out of it (night).
Why do we have day and night?
Earth is a giant ball that spins around an imaginary line called its axis. The Sun can only light the half of Earth that faces it. When your part of Earth faces the Sun, it is day. When Earth has turned your part away from the Sun, it is night.
Does the Sun go around Earth?
No. The Sun only looks like it moves across the sky. Really, Earth is turning. It is like riding a roundabout: the trees seem to move past you, but you are the one going round.
How long does Earth take to spin once?
About 24 hours, which is one day and one night together. In the 3D model, one full turn takes about 18 seconds.
Which way does Earth spin?
Earth spins from west to east. That is why the Sun seems to rise in the east in the morning and set in the west in the evening.
Is it night everywhere at the same time?
No. At any moment about half of Earth is having day and the other half is having night. When it is night in India, it is daytime in places on the other side of the world, such as the USA.
Where does the Sun go at night?
Nowhere. The Sun keeps shining all the time. At night your side of Earth has simply turned away from it, so the Sun is lighting the other side.
What the 3D model shows
The model shows Earth as a realistic globe with the Sun to the left. Sunlight lights the left half of Earth, and the right half is in darkness, where you can see city lights. A red pin marks India. When you press Play, Earth turns from west to east, about once every 18 seconds. The pin moves from the bright half into the dark half (sunset), across the night side, and back into sunlight (sunrise). A small sky picture shows what the sky in India looks like at each moment, and the panel shows the approximate time of day and how high the Sun is in India’s sky.
Common mix-ups
- “The Sun moves around Earth.” The Sun only seems to move; Earth is spinning.
- “The Sun goes out or hides behind the Moon at night.” The Sun keeps shining; your side of Earth has turned away.
- “Earth going around the Sun makes day and night.” Going around the Sun takes a whole year and helps give us seasons. Day and night come from Earth spinning.
- “It is night everywhere at once.” Half the world always has day while the other half has night.
Remember
Earth spins, so each place takes turns facing the Sun (day) and facing away from the Sun (night).
For grown-ups: things to ask
- Before pressing Play, ask: “Where do you think India will be when it is night?” Then check together.
- Ask: “If it is morning for us, what time might it be for someone on the other side of the world?”
- Try it at home: shine a torch at a ball or globe in a dark room and slowly turn it. Put a sticker on your country and watch it go from light to dark.
Going deeper (ages 9–11)
What is Earth’s axis, and why is it tilted?
The axis is the imaginary line from the North Pole to the South Pole that Earth spins around. It is tilted by about 23.4 degrees. The tilt does not cause day and night, but it changes how long days are during the year and helps cause the seasons.
Why do sunrise times change during the year?
Because Earth’s axis is tilted, places get longer days for part of the year and shorter days for the rest. The model shows a time near the March or September equinox, when day and night are about the same length almost everywhere.
Why does the sky glow before sunrise and after sunset?
Even when the Sun is just below the horizon, sunlight still lights up the air high above you. That glow is called twilight.
What this model simplifies
- Earth, the Sun and the distance between them are not to scale. The real Sun is about 109 times wider than Earth and very far away.
- The model shows one time of year (near an equinox). At other times, days and nights are longer or shorter.
- The time shown is “Sun time”, which can differ from clock time by up to about an hour.
- Clouds and city lights are from real satellite pictures but are simplified.
Sources
- NASA Space Place: What is a day?
- NASA Space Place: What causes the seasons?
- BBC Bitesize: Light and shadows (half the world is always in shadow)
Last updated 10 November 2026. Made by Akhil Paul. Interactive lessons are free to use.