读者刘昕问:“为什么月亮会随着人一道行进?”这个问题是我们日常生活中经常遇到的一种现象.例如,当我们坐在行驶中的火车(或汽车)里往窗外望,就会感觉远处的景物(如房屋、树木)随火车一起行进,而火车旁的房屋、树木却反向而行.这种由于观察地点变化,而觉得远近两物体产生移动的现象,称为视差.图1中的箭头表示一列由南向北行驶的火车,A和B代表坐在火车上的人的先后观察点,s_1和s_2分别 Readers Liu Xin asks: “Why does the moon travel with people?” This problem is a phenomenon often encountered in our daily life. For example, when we sit in the middle of a moving train (or car) You can feel the distant scenery (such as houses, trees) along with the train, and the train next to the house, the trees are the opposite .This observation site changes, and feel near and far the phenomenon of the movement of two objects, known as Parallax. The arrow in Figure 1 shows a train traveling from south to north, A and B representing the successive points of sight of people sitting on the train, s_1 and s_2, respectively