How do foreigners explain the full moon and the lack of the moon (we mean the first day and the fifteenth day)

1. Check the astronomical catalogue. The earliest astronomical catalog is to indicate the position and phase information of the sun, the moon and the five stars, and everything is available.

2. Since the early Qing Dynasty, the official calendar of China has been calculated by astronomical methods from the west. Ancient astronomy in China was calculated by algebraic method (interpolation method), that is, a two-dimensional model. Without considering the distance between planets, the error will increase with time. Western astronomy inherited the tradition of ancient Greece and established a more scientific geometric model.

3. Calendars are divided into solar calendar, pure lunar calendar and combined calendar of yin and yang. These three kinds of western and western, China's lunar calendar and solar terms are all part of the solar calendar.