Concept:Earth Day in geography refers to the time taken by Earth to complete one rotation on its own axis.
Explanation:Earth has two main motions: rotation (spinning on its axis) and revolution (orbiting the Sun).
Rotation causes day and night. As Earth is spherical, only half faces the Sun at any moment — that half experiences day, the other half night.
The imaginary line dividing day and night is called the circle of illumination.
Earth takes about 24 hours to rotate once completely around its axis.
This period of one full rotation is known as Earth Day.
It is also called the daily motion of Earth.
The other options are incorrect: option A describes equinox, option B describes revolution, and option C describes longitude spacing.
Answer:D. The period of one rotation of the earth around its axis