If the Earth spins eastward, why does the Sun rise in the east?

A lamp and a globe

Put a lamp in a dark room and a globe in front of it. At any moment exactly half the globe is lit and the other half is dark. There is never a stage where all of it is lit or all of it dark.

Now turn the globe slowly. The boundary between light and dark creeps across it, and every point passes from light into dark and back again — once a day.

That is all of it. Nothing else is needed to explain day and night: one light source, one ball, one spin.

Why it looks as though the Sun moves

When you sit on a train leaving a station, for a moment it looks as though the station is sliding backwards. Your eye compares you to your nearest surroundings, not to the track.

The same thing happens here at a different scale. We travel eastward very fast without feeling it, because everything around us travels with us — the air, the buildings, the sea.

So the Sun 'rises' in the east: we are turning towards it from there. And it 'sets' in the west: we keep turning until it disappears behind the line.

Time zones

If half the Earth is lit at any moment, one clock time cannot suit everybody. When it is noon in Israel, somewhere else the Sun is setting at that very instant, and somewhere else again it is midnight.

The globe is divided into about 24 time zones, one for each hour of the day. East of us the time is later; west of us it is earlier.

The arithmetic is simple: count the zones between, then add or subtract that many hours. It is why a flight to Japan 'steals' a day and the flight home gives it back.

Worked examples

1. It is 14:00 in Israel. New York is seven hours behind. What time is it there?

   1. New York is west of us, so its time is earlier
   2. Subtract seven hours
   3. 14 minus 7

   Answer: 07:00 the same morning

2. How much of the Earth is lit at any given moment?

   1. One light source lights half a ball
   2. The rest is in the ball's own shadow

   Answer: Exactly half lit and half dark, always

3. Why can we not feel the spin?

   1. The speed is steady and does not change
   2. The air, the sea and the buildings travel with us
   3. There is no acceleration to feel

   Answer: Because everything around us moves at the same speed, as on a smooth train

Common mistakes

Saying the Sun moves across the sky

The Sun stays where it is relative to us through the day. What moves is the ground under our feet, eastward, once a day.

Confusing the daily spin with the yearly orbit

The spin on its axis gives day and night and takes a day. The orbit round the Sun gives the year and the seasons and takes 365 days.

Thinking another country simply 'decides' its time

The time follows from where you are on the ball. When it is noon here, the Sun is somewhere else entirely in somebody else's sky.

More in Earth and Space

• How can anyone tell the Earth is round without going to space?
• Is summer hot because the Earth is closer to the Sun?
• Why does the Moon change shape — is it the Earth's shadow?
• If the Moon goes round us every month, why is there not an eclipse every month?
• What holds the planets in their orbits?