Geographical knowledge of the fifteenth full moon of the lunar calendar

The moon shines by reflecting sunlight, which is different from the relative position of the sun (longitude difference), so it will take on various shapes.

As shown in the figure, at the position of 1, the longitude difference between the sun and the moon is 0. At this time, the moon is located between the earth and the sun, with its dark side facing the earth and appearing almost at the same time as the sun, so it can't be seen on the ground. This is the new moon, the first day of the lunar calendar.

The first quarter of the new moon: the moon continues to rotate forward. On the eighth day of the seventh lunar month, that is, position 3 in the picture, the longitude difference is 90. The sun went down and the moon was already overhead. It didn't fall until midnight. At this time, just half of the moon illuminated by the sun can be seen by you. This is the so-called "first quarter moon".

Full Moon: On the 15th and 16th day of the lunar calendar, the moon turns to the other side of the earth, that is, position 5 in the figure, with longitude difference of 180. At this time, the earth is between the sun and the moon, and the half moon illuminated by the sun is just facing the earth. At this time, we see the full moon, or "looking". Because the moon is just opposite to the sun, the sun sets in the west and the moon rises in the east. When the moon sets, the sun rises in the east, and you can see the bright moon all night.

After the full moon in the first quarter, the moon rises later every day, and the bright part of the moon gets smaller every day. By the 23rd day of the lunar calendar, that is, position 7 in the figure, the longitude difference is 270. The full moon is half lost, and then half a moon only appears in the eastern sky in the middle of the night, which is the "lower chord".

Near the end of the month, the moon will rotate between the earth and the sun again, and the waning moon will rise in the east shortly before sunrise. On the first day of next month, it is a new moon, and a new cycle begins.

Fold the moon and the moon of Wang Shuo.

When the sun, the earth and the moon are roughly in a straight line, it is the time when the moon on the earth is full and short. After that, the moon orbits the earth 360 degrees relative to the star, lasting about 27.3 days, which is regarded as the movement cycle of the moon. Because this fillet is relative to the star, the corresponding period is called the sidereal moon. During this time, the earth has to move a certain distance around the sun, and at this time the sun, the earth and the moon have a certain angle. It takes about 2.2 days for the moon to move with the earth to reach a new position. Finally, the three stars are approximately collinear again, and then the full moon on the earth appears again. So for the earth, the phase change of the moon can be regarded as a cycle, and it will appear again, so this cycle is called the full moon. The duration is approximately 27.32 days +2.2 1 day =29.53 days. Therefore, Wang Shuo's moon time is longer than that of the star moon. The orbit of Wang Shuo's moon around the earth is 360+360× 29.53/365.24 = 389.11,and the calculation of the star moon is about 0.

There is an included angle of 5 degrees between the orbital plane of the moon around the earth (ecliptic plane) and the orbital plane of the earth around the sun (ecliptic plane), so at the new moon or full moon, the moon, the earth and the sun are often not a straight line. When there is a straight line between the earth and the sun in a month, a solar eclipse (at new moon) or a lunar eclipse (at full moon) can be observed. It is precisely because of this 5-degree tilt that there are new moons and full moons every month, but there is no eclipse every month.

In addition:

It (lunar calendar) mainly refers to the calendar arranged according to the moon phase cycle in astronomy. A month is the orbit of the moon around the earth (with the sun as the reference, the actual moon runs for more than one week), that is, the calendar based on the first month of the lunar calendar. In agrometeorology, it (Lunar Calendar) is commonly known as lunar calendar, lunar calendar, ancient calendar and old calendar, which refers to the traditional summer calendar in China. Astronomically, it is actually a kind of lunar calendar.