There is a day and night because of the rotation of our earth. There is a difference between revolution and rotation. The earth revolves around the sun meaning it comes around the sun in its path of motion called orbit. At the same time, the earth also rotates on its own axis. Its axis refers to an imaginary line drawn between the earth’s North and South Pole. The rotation is similar to what happens when you spin your toy. But remember that the earth is not spinning upright. There is a tilt of 23.50 degrees while earth spins towards east.
Having learnt what revolution and rotation are, let’s see how long the earth takes to complete one revolution around the sun and one rotation on its own axis. The earth takes about 365 days (1 year) to complete a revolution and about 24 hours (1 day) to complete a single turn or rotation.
Every morning, you get up seeing the sun rising in the east. By evening it sets in the west. We experience day and night alternately. How does this happen?
Due to its rotation, at any point of time only one half of the earth would face the sun. The other half facing away from the sun receives no light from sun and is completely dark. The time during which the side of earth faces the sun is the ‘day time’. There is enough light from the sun that keeps the day bright. When the same side of the earth rotates to the side ‘not’ facing the sun, night befalls. There is no light from the sun leading to darkness. Though Sun is stationary, we say sun rises in the east and sets in the west. This is again because the earth rotates. Further, since the axis of earth is tilted, different places on earth experience unequal days and nights. But near equator, day and night are of almost equal duration, 12 hours each. Artic and Antartic regions experience polar day and polar night. Polar day occurs when sun stays for more than 24 hours. Similarly, polar night occurs when sun is away for more than 24 hours.