Day and Night
The sun moves over the sky and reveals the blue sky. Soon it moves towards the horizon and silence and darkness sets in. This is day and night. You have seen this many times.
The Reason for Day and Night
The the sun does not move, but rather the world you live on is turning towards the sun. At one time half of the earth is covered with light from the sun and the other half is in darkness. No sunlight can fall on the dark side, until the earth turns.
The 24-hour Cycle
There is a 24-hour day/night pattern as a result of one full rotation of the earth around its own axis. This is referred to as diurnal cycle. This pattern is seen in the environment and in the climate. Our body also has an internal clock that affects our mood, mental alertness, hunger, and heart function.
Our biological clock is thrown off when we do things that are out of the ordinary.
We all have an internal body clock. It gives us the idea to sleep, relax, or eat. If you want to stay in the 24-hour cycle, your must ensure your brain get the sunlight it needs each day. We also must make sure we eat healthy foods in order to keep up with our internal body-clock.