Question

Define the circle of illumination.

Answer 1

Circle of illumination is an imaginary line that separates light from darkness and day from night. Earth's axis refers to an imaginary line going through the center of the earth from top to bottom.

Answer 2

The circle of illumination is the division between day and night over the earth. The circle of illumination bisects (cuts in half) all latitudes on the spring and autumnal equinoxes. At this time, all places have equal day length (12 hours). The circle of illumination always bisects the equator (0 degrees latitude).