Darkness is when there no light. In practice, out in the open air, there almost always is some light, however slight. The darkness of the night sky is estimated by a nine-point scale known as the Bortle scale.
Darkness is made by blocking light from the sun or some other source of light, which makes shadow. At night the Earth blocks the sun, and casts a shadow over one entire side of the world. There is heat radiation even in the dark.
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