Constellation knowledge: Why is the moon sometimes round and sometimes missing?

The moon is very familiar to us. We will find that the moon is sometimes round, sometimes it is not round, but curved, with a corner missing. Then why? Then we will use the knowledge of constellations to reveal why the moon is sometimes full and sometimes missing.

Why is the moon sometimes round and sometimes short?

The moon is round and short, which can be divided into two situations: one is the phase change of the moon, and the other is the eclipse phenomenon. When the moon revolves around the earth, the relative positions among the earth, the moon and the sun are constantly changing. Because the moon itself does not emit light, but only reflects sunlight, people see that the illuminated part of the moon is constantly changing, which is the phase change of the moon. Solar eclipse is a special astronomical phenomenon. When the moon moves to the shadow of the earth, the area between the moon and the earth will be covered by the sun, and the moon will change. That is to say, at this time, the sun, the earth and the moon are just (or almost) on the same straight line, so the light from the sun to the moon is blocked by the earth, which makes the eclipse happen.

Data expansion:

The phase of the moon is calculated by the difference between the sun and the moon (the following degrees are the difference between the sun and the moon), and * * * is divided into eight types:

New moon (the first day of the lunar calendar, the new moon): 0 degrees;

Upper Emei month (usually around the second day of February-around the seventh day of July): 0-90 degrees;

First quarter moon (around the eighth day of the lunar calendar): 90 degrees;

Convex moon (around the ninth day of the ninth lunar month-around the fourteenth lunar month): 90 degrees-180 degrees;

Full moon (full moon, 15th or 16th lunar month): 180 degrees;

The waning moon (around the 16th lunar month-around the 23rd lunar month): 180 -270;

First quarter moon (around the 23rd lunar month): 270 degrees;

Lower Emei month (around the 24th day of the lunar calendar-the end of the month): 270 -360 degrees;

In addition, the last day of the lunar month is called a dark day, that is, you can't see the moon.

There are mainly four kinds of moon phases: new moon (the first day of the lunar calendar), first quarter moon (around the eighth day of the lunar calendar), full moon (around the fifteenth day of the lunar calendar) and last quarter moon (around the 23rd day of the lunar calendar), all of which have definite occurrence times and are calculated by precise orbit calculation.