The Circle of Illumination is an imaginary line that separates the areas of Earth which are currently experiencing daylight from those that are in darkness. When the Earth rotates on its axis, one half is facing towards the Sun and experiencing daylight, while the other half is facing away from the Sun and is in darkness.

Option 1, "East and West," is incorrect because the Circle of Illumination does not divide Earth based on its eastern and western hemispheres. Instead, it separates the areas of daylight and darkness.

Option 2, "North and South," is incorrect because the Circle of Illumination does not divide Earth based on its northern and southern hemispheres. It is a boundary between day and night, not between the northern and southern regions.

Option 4, "Summer and Winter," is incorrect because the Circle of Illumination is not associated with the seasons. It is solely related to the division between day and night.

The correct answer is option 3, "Day and Night," as it accurately describes how the Circle of Illumination divides Earth into the areas experiencing daylight and darkness.