The best time for stellar observation is after the end of evening twilight and before the begining of morning twilight 每天最理想的观测时间是由昏影终时开始至晨光始时结束。
2.
The twilight before sunrise and after sunset is due to the scattering of sunlight by the atmosphere . the time of begining and end of twilight depends on the local geographic and climate conditions 日出前和日没后的一段时间内天空呈现出微弱的亮光，这现象叫做晨光和昏影，这是由于大气的散射所引起。
