The rotation of the Earth is defined as the length of time it takes to rotate once on its axis. This appears to be done once a day, or every 24 hours. However, due to the effect of solar gravity, the rotation is not exactly 24 hours but about 23 hours and 56 minutes.
The average distance between the Earth and the Sun is about 93 million miles (150 million km). Because of this distance, the Earth travels through space at about 30,000 miles per hour (48,000 kph), which is very fast for such a large body.
During a day the Earth goes through all angles from north to south, taking one full circle. At the end of this circle, it starts over again at the same place it started in the morning. The period of time it takes the Earth to go through one complete rotation is called a day. The day can be divided into two parts: night and day. Night begins when the Earth is facing away from the Sun and ends when it faces toward the Sun. Day begins when the Earth has turned around so that it is facing away from the Sun and ends when it has turned around so that it is facing toward the Sun.
Every 24 hours, the Earth rotates on its axis. The sun appears to move across the sky as the Earth spins, but it is actually the Earth that is rotating. One rotation takes 24 hours to complete, which is why there are 24 hours in a day. As the Earth turns, so too will all living things on it. With respect to the fixed stars, everything on Earth except for the south polar region of Antarctica is in some part of the orbit of the moon. Thus, every part of the world has experienced both night and day since the moon began its monthly cycle around the Earth many years ago.
As the Earth orbits the Sun, the distance between them changes. On average, the Earth is about 150 million km from the Sun (about 93 million miles). But because of the Moon's influence, the distance varies as well. When the Moon is full, it is about 508,000 km from the Earth (about 304,000 miles). When it is new, it is about 239,600 km (about 144,900 miles). These ranges in distance cause problems for us here on Earth: For example, when the Moon is full, it blocks out most of the sunlight falling on it, causing a period of darkness known as a lunar eclipse. New moon means no blocking out of the light, so there is almost always some of the sky visible during twilight.
But we know the Earth rotates because we observe the consequences of it every day. Every 23 hours and 56 minutes, the Earth completes one complete revolution on its axis, which is rounded up to 24 hours. Is this a time you've heard before? One day is equal to the time it takes Earth to complete one rotation in 24 hours.
We can calculate the number of rotations per hour by using this formula: 1 rotation per hour = 60 degrees per minute. 1 degree is about 57.3 minutes so 1 rotation is equivalent to 2 degrees or 180 degrees. This means that the Earth makes one full rotation in exactly 24 hours from any given point on its surface.
In fact, if we were able to fly over the entire planet with a helicopter large enough to see around the edges, we would find that the whole thing was wrapped tightly around the axis of the Earth like a belt. The part that is down is today's land, and the part that is up is tomorrow's land. This wraps the Earth like a belt, giving it a complete rotation in 24 hours.
As far as we can tell, the Earth doesn't move anywhere else during its rotation. If it did, then where would it go? It would travel around the center of the Earth until it reached another part of itself, where it would do the same thing all over again!
The Earth revolves once every 24 hours in relation to the Sun, but once every 23 hours, 56 minutes, and 4 seconds in relation to other, distant stars (see below). Because the Earth's rotation slows gradually with time, a day used to be shorter. But since the Industrial Revolution, humans have been using up energy at a rate that outstrips any possible replenishment, so today's days are longer than ever before.
As well as daily changes in light and darkness, the Earth also has a permanent night side and day side. The night side is where we live, but the day side has different properties depending on whether or not you're looking at land or ocean. On the land, there is dark soil and dark rock exposed at the surface. In the oceans, there are many things that cause lights at the surface of the water. Lights from cities and boats come from oil refineries which release chemicals that go up in flames at night; fires are also visible at night. Lights from beneath the sea floor are called "tic patterns" and they're caused by tiny organisms that move up toward the surface during the day and back down again at night.
Day and night happen because the Earth has two different rotational speeds that depend on where you are on its surface. If you're standing on the North Pole, the whole planet spins very quickly around your body. This is called "rotation about a central point".