Answer:
the terminator.
Step-by-step explanation:
The line separating the dark half of Earth from the lighted half is called the terminator. The terminator is the boundary between the day and night sides of Earth, and it changes position depending on the time of day and the season of the year.
During the day, the terminator is located along the edge of the Earth's shadow, which is the dark region on the side of the Earth that is not illuminated by the Sun. As the Earth rotates on its axis, the terminator moves across the surface of the planet, dividing the lighted and dark halves of the Earth.
The position of the terminator is determined by the angle of the Sun's rays and the orientation of the Earth's axis. At the equator, the Sun's rays are perpendicular to the Earth's surface, and the terminator is located at the center of the day and night sides of the Earth. At higher latitudes, the Sun's rays are more oblique, and the terminator is located closer to the poles.
The terminator is an important concept in the study of Earth's climate and weather, as it affects the distribution of heat and light across the planet's surface. It also plays a role in the daily rhythms of plants and animals, as the movement of the terminator across the Earth's surface signals the onset of day and night.