Day and night


Why does the Earth spin?
The Earth spins because of the way it was made. It was made from some of the dust in the swirling cloud of gas and dust that made the Solar System. As the dust particles swirled together they collided to make our spinning planet, the Earth.

Which way does the Earth spin?
If you could look down on the North Pole of the Earth you would see that the Earth spins in an anticlockwise direction. As the Earth spins, the Sun appears to move across the sky in the daytime as the diagram shows.



What would happen if the Earth did not spin?
One half would have daylight all the time and be very warm. The other side would be in the dark all the time and be very cold.

Do other planets spin?
All the planets spin. The slowest spinning planet is Venus which takes 243 Earth days to spin round once. The fastest spinning planet is Jupiter. It takes just nine hours fifty minutes to spin round once.

What would it be like on Earth if it spun like Venus?
If the Earth spun like Venus and sunrise began on January first, sunset would not occur until the first of May, and then it would be night until the end of August. The Sun would appear to go the opposite way across the sky because Venus spins in the opposite direction to Earth. It is the only planet to spin clockwise.

What would it be like if Earth spun like Jupiter?
If the Earth spun like Jupiter you would have about five hours of daylight followed by five hours of darkness. A week of seven days would pass in the time we now take to get from Monday to Wednesday.


How does a spinning planet help us?
If our planet did not spin it would tumble as it went around its orbit. One moment its North Pole would be at the top of the planet, the next it might be on its side. The planet could turn upside down, then right way up again. There would be no pattern to day or night, the Sun might go backwards and forwards across the sky or not appear for weeks. These irregular events would make it impossible for life to survive or probably even develop on the Earth four billion years ago. Life depends on a regular supply of energy from the Sun. This supply is delivered at a regular time daily as each part of the planet spins for a time in the sunlight.



How is the Earth like a bullet?
Spinning objects stay on their path. A bullet is made to spin as it passes down the barrel of a gun. This spin keeps the bullet going in a straight line. In a similar way, the spinning of the Earth helps it move smoothly around the Sun as it is pulled by the Sun's gravity.

Has the Earth always spun so fast?
The Earth once spun much faster. Soon after it formed it spun around on its axis once every six hours.

Will an Earth day always be 24 hours?
No. The Earth is slowing down. In millions of years' time it will take 27 hours to spin round once.