The Sun is but a fixed Star!
Day or night, the Sun is fixed at its place in the solar system. It is the Earth’s rotation and spinning that makes the Sun disappear at night.
The Sun is always shining and spreading its light on the Earth. But it cannot provide light on the entire Earth at the same time. The Earth is like a ball which is spinning on its axis. The side which faces the Sun receives Sunlight. The Earth keeps spinning and the Sun facing side later experiences evening and then night when that side has moved away from the Sun. Now the other side of the Earth is facing the Sun.
The rotation of the Earth
As the Earth continues to spin, the day side turns away from the Sun, thus giving the impression that the Sun is going down or the Sun is setting. When the night side of the Earth starts to face towards the side of the Sun, it gives the impression of Sun rise.
So, it is not the Sun that is going away anywhere. It is the Earth that you are on that is spinning.
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