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Your child asks why it gets dark at night. "The Earth spins" rarely sticks. A few minutes with a torch, a ball and a dark room works better, and sets you up for the next question: why is it night in America when it is day here?
Why do we have day and night?
Earth is a ball lit from one side by the Sun, so at any moment half of it is in sunlight and half is in shadow. NASA's StarChild page for young learners puts it simply: when your part of Earth points towards the Sun it is day, and when Earth rotates you away from the Sun it is night.
One full turn, measured from noon to noon, takes 24 hours, which is the length of a day in NASA's Earth fact sheet. The Sun does not go anywhere at night. You are simply on the side of Earth facing away from it.
How do you show day and night with a torch and a ball?
You need a torch (a phone light works), a ball or an orange, a pen and a room you can make dark. NASA's StarChild page suggests the same idea with a globe and a bright light, and the International Astronomical Union's astroEDU activity on day and night uses a ball and a flashlight for children aged 6 to 12.
Mark a small dot on the ball and say "this is our home". If you like, add a second dot on the opposite side for a cousin abroad.
Put the torch on a table so it shines steadily at the ball. The torch stays still, just as the Sun does.
Switch off the room lights. Ask: "Which half of the ball has day right now? Which half has night?"
Turn the ball slowly, anticlockwise if you look down on its top (the North Pole), as NASA's StarChild page describes. Stop when the dot reaches the edge of the light and say "sunrise".
Keep turning to the middle of the light ("lunchtime"), then to the far edge ("sunset"), then into the dark ("bedtime").
Hand the ball over and ask your child to make it morning for the cousin. Doing it with their own hands shows you whether the idea has landed.
What will my child probably believe first?
In a 1994 study of first, third and fifth graders, Stella Vosniadou and William Brewer found that younger children explained night from everyday experience, for example that the Sun goes down behind mountains or clouds cover it. Older children tended to build mixed models, such as the Sun and Moon circling a still Earth every 24 hours, and only a few of them gave an explanation close to the scientific one.
So a child who says "the Sun sleeps behind the hills" is explaining what they see. Ask "what would we see if that were true?" and then let the torch test it.
Why is it night in America when it is day in India?
This is where the dot on the other side of the ball pays off. Earth turns 360 degrees in 24 hours, so it turns 15 degrees every hour, as NASA's lesson on latitude and longitude shows. NOAA explains that this 15 degrees per hour is why the world has 24 time zones, though real borders bend to suit countries.
A worked example you can do together:
India keeps one clock, Indian Standard Time, which CSIR-NPL's national time display gives as UTC + 5:30.
5 hours 30 minutes is 5.5 hours, and 5.5 × 15 = 82.5. So IST is the clock time of a line 82.5 degrees east of Greenwich.
A place on the other side of Earth is about 180 degrees away, and 180 ÷ 15 = 12 hours. When your dot sits in the middle of the light, a dot opposite it sits in the middle of the dark.
What questions might come next?
Why don't we feel Earth spinning? Using the equatorial radius in NASA's fact sheet, the equator is about 40,075 km round, so it moves at about 1,670 km per hour. We move with it smoothly, like passengers in a steady train.
Why are summer days longer? That comes from Earth's tilt, and our guide to explaining seasons with a globe and lamp uses the same kit.
Do astronauts get day and night too? Yes, many times a day: see how many sunrises the space station sees.
If your child wants to keep exploring on a screen after the torch goes off, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than to read. For the next eclipse or rocket launch in the news, try these tips on talking to kids about science news.
