The circle of illumination is the dividing line on Earth that separates the daylit side from the night side. It represents the boundary between areas receiving sunlight and those in darkness. This circle constantly shifts due to the Earth’s rotation, creating the cycle of day and night across the globe.
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The circle of illumination is the imaginary line that divides the Earth into its day and night sides. It marks the boundary where sunlight stops illuminating the planet, separating areas in daylight from those in darkness. As the Earth rotates on its axis, this circle moves continuously, causing the progression of day into night and vice versa. The circle of illumination is not aligned with the Earth’s axis due to its 23.5-degree tilt, which results in varying lengths of day and night throughout the year. This phenomenon is also responsible for the changing seasons as different parts of the Earth receive varying amounts of sunlight.