Concept:The circle of illumination is the imaginary line that separates the sunlit day side from the dark night side of the Earth. Explanation:As the Earth rotates, only half faces the Sun at any time. This creates a boundary where day ends and night begins. This boundary is a great circle, not aligned with longitudes, because of the Earth’s axial tilt. For any given moment, this circle continuously moves as the Earth spins. It is not fixed; it shifts with the seasons and time of day. The correct definition is simply the dividing line between daylight and darkness.
Answer:B. circle that divides the day from night on the globe
