Why sometimes the sun and the moon shine together, and sometimes they don't?

The meanings and symbols of the sun and the moon are as follows:

Symbol: In the realistic environment of ancient times, it is a good omen for the sun and the moon to shine together. Duke Zhou called "Sun and Moon" Ming, which means "good luck". In ancient times, some people made this into an inkstone, which means that the future is bright and the promotion is step by step.

Moral: People think that the sun and the moon shine together is an astronomical wonder, so when the sun and the moon shine together, they often think that auspicious events have taken place in the country and the nation. In fact, in theory, this phenomenon can be seen except on the fifteenth day of the lunar calendar every month.

Physical phenomenon that the sun and the moon shine together;

The sun and the moon are just a natural phenomenon, which requires the sun and the moon to be above the horizon at the same time. Theoretically, as long as the atmospheric conditions are good, this phenomenon may occur except the fifteenth day of the lunar calendar.

But there is a second condition, that is, the limit magnitude of the sky (the darkest celestial body that can be seen) cannot be too low, so generally speaking, when the sun rises or is about to set, the brightness of the sky can easily meet this condition (even in cities).

So in the first half of the lunar calendar (after the fourth day of the lunar calendar), you can see the moon phase when the sun goes down, from west to east in turn.

In the second half of the lunar calendar (before the 27th), you can also see the moon after the sun rises, from the western sky to the eastern sky.