What does it mean that the sun and the moon shine together?

It means that the sun and the moon shine together, or the sun and the moon appear at the same time.

Sunrise is a natural phenomenon, which is caused by the different rotation periods of the earth around the sun and the moon around the earth. Direct observation of the sun, moon and sky with naked eyes requires certain conditions. Generally, it can only be seen in broad daylight when the sky is clear and the visibility is good from February/Kloc-0 to March in the autumn lunar calendar.

Extended data

Sun-moon tonghui principle

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).

Therefore, 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, and from west to east in turn after the sun rises in the second half of the lunar calendar (before the twenty-seventh day).