一、晨昏线与昼夜更着。由于地球是个不透明的球体,在太阳光的照射下,出现了半个地球面向阳光而明亮,半个地球背向阳光而黑暗的现象。对于地球上的人们来说,这个明亮的半球就是昼半球,这个黑暗的半球就夜半球。而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,是由晨线和昏线所组成的大圆。晨昏线随着地球的自转运动而不停地自东向西移动着,这对于地球上的人们来说就是昼夜更替现象。在地球自转运动中,由夜半球进入昼半球的分界线叫做晨线,由昼半球进入夜半球的分界线叫做 First, the twilight line and stay up late. Because the earth is an opaque sphere, under the illumination of the sun, half of the earth faces the sun and is bright, and half of the earth is back to sunlight and dark. For people on Earth, this bright hemisphere is the hemisphere, and this dark hemisphere is at night. The dividing line between the hemisphere and the night hemisphere is the dawn and dusk line. The twilight line is also called the dazzling coil. It is a big circle made up of the morning line and the dark line. The twilight line moves from east to west as the earth rotates. This is a phenomenon of day and night for people on Earth. In the rotation of the earth, the boundary line that enters the hemisphere from the night hemisphere is called the morning line, and the boundary line from the hemisphere into the night hemisphere is called