Question

what are the circle of illumination?

Answer 1

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).

Answer 2

the circle that separates day and night is called circle of illumination.