海市蜃楼发生时能够返回地面之光线的初始角探讨

Discussion on the initial angle of light rays being able to return to the ground in mirage

从真空中光速最大事实和折射定律(或光线轨迹方程)出发,证明:大气中能够返回地面之光线的初始角α是不能任意的,且当α大于某个值α_m时,从某点发出的光线不可能返回地面,同时给出影响α_m的其他因素.

Starting from the fact that the speed of light in a vacuum is the largest and the law of refraction （or ray trace equation） , it is proved that the initial angle α of the light ray being able to return to the ground in mirage can not be arbitrary. When α is greater than the certain value αm, the light emitted from a point is not able to return to the ground. The other factors affecting αm are also given.