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由于地球的公转在一年中,太阳的直射点在南北回归线之间来回移动,这反映在南北半球所得到的光热不同,季节自然相反。又因各纬线圈受到阳光照射的弧长短不一,(如甲、乙图)所以不同的纬度,昼夜长短就有所差异。由于地球的自转,在一昼夜中,太阳对各条经线的照射情况是不同的,当太阳移至某一经线的最高位置时(不一定是直射,只有南、北回归线之间的那一段经线才有得到直射的机会)该经线就是正午(12时)。如下列各图所示的正午时刻所处的经线都不一样,必须确定处在正午的经线后,才能够根据时区和日界线的基本知识(每一时区跨经
Because of the revolution of the Earth in one year, the direct point of the sun moves back and forth between the Tropics of the South and the North. This reflects the difference in the light and heat obtained in the northern and southern hemispheres. The seasons are naturally opposite. Because of the different lengths of the arcs that are exposed to sunlight in the individual weft coils (such as A and B maps), there are differences in the length of day and night at different latitudes. Due to the rotation of the earth, in the day and night, the sun’s illumination of each warp is different. When the sun moves to the highest position of a warp (not necessarily direct, only the warp between the tropics There is a chance of getting a direct shot.) The warp is at noon (12 o’clock). As shown in the following figures, the meridian lines at the time of midday are different and must be determined after the mid-day meridian to be able to base on the basic knowledge of the time zone and date line (each time zone spans