太阳每日东升西落的现象,是由于地球自西向东自转造成的。当太阳通过当地子午圈的瞬时定为12时整;这样计算的时间,叫做地方时。很显然,不同的经度就有不同的地方时,而且东边的地方时总是早于西边的地方时。人们曾经长期使用地方时,但是,由于交通、电讯的发展和地区间的联系日益频繁、地方时因经度而不同的缺点就突出地表观出来了。 The phenomenon of the sun rising from east to west each day is caused by the rotation of the earth from west to east. When the sun passes through the local meridian circle, it is set at 12 o’clock; this time is called local time. Obviously, different longitudes have different places, and when the east side is always earlier than the west side. When people used the place for a long time, however, due to the increasing frequency of traffic, telecommunications, and connections between regions, the shortcomings of local differences in longitude were prominently observed.