Variation characteristics of full moon and lack of moon

In the vast starry sky, the most striking celestial body will light up in a few months. Its ever-changing appearance and the beautiful myths and legends it carries from ancient times to the present have added a lot of poetry and painting to this world! In Guanghan Palace, there is a jade building in Qionglou, where Chang 'e dances. Not only that, the periodic ups and downs of the moon are also one of the bases for people to make calendars since ancient times.

The moon revolves around the earth and rotates at the same time. The two periods are the same and the direction is the same, so the moon always faces the earth on the same side. In the long years before the satellite went into the sky, people never saw the back of the moon.

Why does the moon change? As we all know, the moon itself does not shine, but only reflects part of the sunlight that shines on it. In this way, for observers on the earth, with the change of the relative positions of the sun, the moon and the earth, the moon presents different shapes on different dates, which is the periodic change of the moon phase. Furthermore, although the moon is always illuminated by the sun, and the half sphere is bright, because the moon is constantly revolving around the earth and changing its position, the half sphere facing the earth and the half sphere illuminated by the sun sometimes completely overlap, sometimes completely do not overlap, sometimes a small part overlaps, and sometimes most of them overlap, so the moon presents a cloudy or sunny change.

When the moon is between the sun and the earth, its dark hemisphere is facing us, and we can't see any images of the moon at all. This is the "new moon". In astronomy, the new moon refers to the moment when the yellow meridian of the moon is the same as the yellow meridian of the sun. On the first day of the new moon, the moon and the sun rise from the east at the same time. Even if the earth reflects sunlight to the moon, the part of the light reflected by the moon will be completely submerged in the strong sunlight.

When the earth is between the moon and the sun, although the three planets are also on the same line, at this time, the moon hemisphere illuminated by the sun is facing the earth, and the soft moonlight shines on the earth all night. This is the full moon, which is "looking". At this time, the difference between the lunar longitude and the solar longitude is 180 degrees.

Because the distance between the moon and the earth is too short compared with the distance between the sun and the earth, the speed of the moon moving eastward on the celestial sphere is much faster than that of the sun. The moon advances from west to east every day 13 degrees or more, while the sun only advances 1 degree. Therefore, after the new moon, the moon quickly ran to the east of the sun. A day or two later, as soon as the sun goes down, a crescent moon can be seen in the western sky, with two sharp corners pointing to the east. From then on, the moon rose later and later, and it gradually became round. About seven days after the new moon, the yellow meridian of the moon just exceeds the sun by 90 degrees. The moon we see is a semicircle, and the arc faces west. This is the first quarter moon. After that, the moon continued to the east, more round, and then rose until it looked out. From the new moon to the moon, the distance between the moon and the sun is getting bigger and bigger.

Looking at the past, the moon gradually moved closer to the sun, and the surface of the moon gradually became thinner. When the yellow meridian of the moon exceeds the yellow meridian of the sun by 270 degrees, it becomes a semicircle again, but the arc faces east, which is the last quarter moon. At this time, the sun rises in the east and the moon is high in the southern sky. Naturally, the moon is invisible to our naked eyes. After the first quarter moon, the moon will not come out from the east until after midnight. Its semicircle is gradually eroded and becomes a narrow sickle with a sharp angle to the west. Looking at the new moon, the moon and the sun are getting closer and closer, and even disappear into the morning light like the ecliptic of the sun.

The cycle of the moon phase change, that is, the time from the new moon to the new moon or from the new moon to the new moon, is called the first month. The observation results show that the length of Wang Shuo's moon is not fixed, sometimes as long as 29 days 19 hours, sometimes only 29 days and 6 hours, and its average length is 29 days 12 hours, 44 minutes and 3 seconds.

The time interval between the moon and a star at the same time is called "sidereal moon", which is the real cycle of the moon's orbit around the earth. Wang Shuo's moon is longer than the star moon, just as the sun is longer than sidereal day. The moon and the stars have little to do with daily life, but it is the ebb and flow cycle of the moon, which is related to the ebb and flow of the earth, navigation and fishing, and has a great influence on people's activities at night. At the same time, it also occupies an important position in the last month of religion, so people naturally regard it as a longer time unit than a day.