We are the ones moving

About this video

Every morning the Sun comes up on one side of the sky, climbs, and goes down on the other side in the evening. For thousands of years most people took the obvious explanation: the Sun travels around the Earth once a day. It turns out the Sun isn't the one moving. We are.

The video looks down on the Earth from above the North Pole. Because the Earth is a ball lit by the Sun, the half facing the Sun has day and the half facing away has night. The Earth also spins around itself, anticlockwise when seen from above the North Pole, once about every 24 hours. Follow one place: it is carried from the dark half into the light (sunrise), faces the Sun (noon), and is carried back into the dark (sunset).

Why does it look as if the Sun moves? On a train that pulls away smoothly, for a moment the platform seems to slide backwards. Your eyes can't tell who is moving, only that something is. Standing on the spinning Earth is the same.

The Earth spins from west to east. As your part of the Earth turns toward the east, the Sun comes into view over the eastern horizon, climbs, and sets in the west. The Moon and the stars rise in the east and set in the west for exactly the same reason.

It is also why it is never the same time of day everywhere. Call your grandparents in China from Canada at lunchtime, and they answer in their pyjamas in the middle of the night, because China is on the other side of the Earth. By the time you go to bed, their morning is beginning.

You can try it with a lamp (the Sun), an orange (the Earth) and a piece of tape (you): turn the orange anticlockwise as you look down on its top, and watch the tape move into the light and out again.

Transcript

1. 0:00Every morning the Sun comes up on one side of the sky, climbs, and goes down on the other.
2. 0:08For thousands of years, most people thought the Sun travels around the Earth.
3. 0:14It turns out the Sun isn't the one moving. We are.
4. 0:20Look down on the Earth from above the North Pole.
5. 0:24Half of it faces the Sun and has day. Half faces away and has night.
6. 0:30And the Earth spins, once about every twenty-four hours.
7. 0:36Follow one place. It turns into the light. Sunrise.
8. 0:40It faces the Sun. Noon. It turns out of the light. Sunset.
9. 0:46Then night, until the next sunrise.
10. 0:50So why does it look like the Sun is moving?
11. 0:54Think of a train pulling away smoothly. For a moment, the platform seems to slide backwards.
12. 1:01Your eyes can't tell who is moving, only that something is.
13. 1:06On the Earth, we turn, and the Sun seems to slide the other way.
14. 1:14The Earth spins from west to east.
15. 1:17As we turn toward the east, the Sun comes into view, climbs, and sets in the west.
16. 1:25The Moon does the same, and so do the stars.
17. 1:30The same spin carries us past all of them.
18. 1:40Ever video-called family in another country?
19. 1:43Call China from Canada at lunchtime, and they answer in their pyjamas, in the middle of the night.
20. 1:51China is on the other side of the Earth, facing away from the Sun.
21. 1:58By the time you go to bed, the Earth has turned, and their morning is beginning.
22. 2:05It is never the same time everywhere.
23. 2:08Try it at home. A lamp is the Sun, an orange is the Earth, and a piece of tape is you.
24. 2:16Look down on the top, the North Pole, and turn the orange anticlockwise.
25. 2:22The tape turns into the light, faces the lamp, and slips back into the dark.
26. 2:32The Sun hasn't moved at all. We have.