Principle: The moon runs between the sun and the earth. If the three are in a straight line, the moon will block the light from the sun to the earth, and the shadow behind the moon will just fall on the earth. Then there will be a solar eclipse.

Features: A solar eclipse is a typical example of light propagating in a straight line in the same homogeneous medium. When the moon moves between the sun and the earth, it is not always like this. There are two conditions for an eclipse to occur.

Cycle: Eclipses always occur on the first day of the lunar calendar. Not all eclipses will happen on the first day of the lunar calendar, because the orbit of the moon (ecliptic) and the orbit of the earth (ecliptic) are not on the same plane. There is an included angle of 59 between the ecliptic plane and the ecliptic plane. Secondly, both the sun and the moon move near the intersection of the ecliptic and the ecliptic, and the sun forms a certain angle with the intersection (eclipse limit).

lunar eclipse

Principle: On the 15th and 16th day of the lunar calendar, the moon runs in the opposite direction to the sun. At this time, if the centers of the earth and the moon are roughly on the same straight line, the moon will enter the umbra of the earth and produce a total lunar eclipse. If only a part of the moon enters the umbra of the earth, a partial lunar eclipse will occur.

Features: It is a special astronomical phenomenon, which means that when the moon moves to the shadow part of the earth, the area between the moon and the earth will be blocked by the earth because of the sunlight, and the moon will be missing.

Period: At this time, the sun, the earth and the moon are exactly (or almost) on the same straight line. Eclipses can be divided into three types: partial eclipse, total eclipse and penumbral eclipse. A solar eclipse can only occur around the fifteenth day of the lunar calendar.