由于地球是个不透明、不发光的球体,在太阳的照射下,便出现了半个地球明亮,半个地球因背向太阳而黑暗的现象。我们把面向阳光的半球称为昼半球,背向阳光的半球称为夜半球。昼半球和夜半球的分界线就是晨昏线。晨昏线也叫晨昏线圈。 Since the earth is an opaque, non-luminous sphere, under the sun’s illumination, half of the earth is bright and half of the earth is dark due to its back to the sun. We call the hemispheres facing the sun the hazy hemispheres, and the hemispheres facing away from the sun are called night hemispheres. The dividing line between the hemisphere and the night hemisphere is the dawn and dusk line. The twilight line is also called the dawn coil.