Day and night

Day and night occurs because the Earth is spinning on its axis.

As the Earth orbits the Sun it spins on its axis once every 24 hours. We call this time one day.

In one day every point on the Earth's surface will come out of night, go through a day, dusk and then into night once more.

If you were standing on the equator you would be travelling round at roughly 1600 km/hour (1000 mph) due to this rotation. At latitude 51^o N you would be moving at just over 100 km/hr (630 mph) as you have a smaller distance to travel in the same time.

Dusk is due to the sunlight filtering through the atmosphere of the Earth. On a planet or moon with no atmosphere the transfer from day to night would be instantaneous with no dusk.

The Sun (and planets, stars and the Moon) rise in the east and set in the west. This means that countries further east of an observer will move into daylight first and so sunrise will be earlier the further east you go.

The first picture is of the sunrise in the east and the second one shows the sunset in the west.

schoolphysics day and night animation

To see an animation of day and night click on the animation link.