The moon is one of the most familiar and important celestial bodies we are most familiar with, and we have longed for the moon since ancient times, praised the moon, and endowed the moon with various beautiful images. The most familiar sentence is "people have joys and sorrows, and the moon is cloudy and sunny", the joys and sorrows in the world are like the changes of the moon, there are shortcomings and perfections.
The moon is "cloudy" and refers to the "moon phase change", which is the different positions of the moon that people see on Earth that are illuminated by the sun. Because the moon itself does not emit light and is opaque, we can see that the bright part of the moon is the part of the moon that reflects the sun's light, and only the part of the moon that is directly illuminated by the sun can reflect the sun's light. We see the part of the Moon that is directly illuminated by the Sun from different angles, and this is where the phases of the Moon come from.
The average period of the Moon's revolution around the Earth relative to the Sun, which we call the synodic month, is actually the average cycle of the moon's phases.
Therefore, "Shuo", to be precise, is the "conjunction" of the sun and the moon, that is, the moon and the sun have the same longitude on the ecliptic, that is, they are in the same direction, and the two appear at the same time, and the moon at this time is called "new moon", which is actually a "moon black sky" where the moon cannot be seen at all. Some people say that when the sun, moon and earth are in a straight line, this is not right, the following picture is a top view from north to south, from top to bottom, so don't be misled (for ease of understanding, the orientation of all pictures in this article is: left, east, right, west, up, south, down, north).
If you look from the side, the orbits of the Moon and the Earth are not on the same plane! That is to say, the white and ecliptic do not coincide, and there is an angle of 5°09′ between them. If you really want to connect the "sun, moon and earth" in a straight line, then you may observe a solar or lunar eclipse.
The Moon reflects the sun's light and is bright, and its relative position to the Sun is different, i.e. the ecliptic longitude, and people can only see its various shapes on Earth.
What is the ecliptic meridian? In the ecliptic coordinate system, the angle between the plane of the ecliptic longitude where the vernal equinox is located and the plane of the ecliptic circle where the celestial body is located, measured in an angle along the counterclockwise direction of the ecliptic, in the range of [0°, 360°]. To put it simply, draw a grid on the celestial sphere based on the ecliptic plane and the ecliptic pole (the intersection point between the straight line perpendicular to the ecliptic plane and the celestial sphere through the observation point), and the horizontal coordinates are called the ecliptic latitude (the angle between the line connecting the celestial body and the center of the celestial sphere and the ecliptic plane), and the longitudinal coordinates are called the ecliptic longitude.
Therefore, the moment when the ecliptic longitude of the sun and the moon is equal, the ecliptic longitude difference is 0°, that is, the moment when the moon is just completely invisible, which is the "conjunction" moment. Correspondingly, the difference between the ecliptic longitude of the sun and the moon is 180°, and the two are far away from each other, the moon at this time is called "Wang" or "Full Moon", the small moon is in the fifteenth, and the big moon is in the sixteenth, and this day is called the Wangri.
The positions of the synods and the stars were determined, and their lines were used as perpendicular lines, and there were two points of intersection with the celestial sphere through the center of the earth, that is, the first quarter and the second quarter moon. The time of the first quarter moon is about the seventh or eighth day of the lunar month, and the yellow longitude difference is 90°, and exactly half of the moon illuminated by the sun can be seen at this time; The time of the second quarter moon is about the 22nd or 23rd day of the lunar month, the yellow longitude difference is 270°, and the full moon is just half lost.
In the remaining days, we see that the thin crescent moon is called the moth eyebrow moon, the moth eyebrow at the beginning of the month, and the lower emei at the end of the month; The fat moon is called the gibbous moon, and the gibbous moon before the full moon is called the waning gibbous moon, or the upper gibbous moon, and the bright part of the moon faces west; The gibbous moon after the full moon is called the waning gibbous moon, or lower gibbous moon, and the bright part of the moon faces east.
It can be seen that the changes in the phases of the moon are as follows: the new moon or new moon (the first day of the new month→ the first quarter moon of the first quarter of the first quarter→ the first quarter of the moon (the seventh and eighth months of the first month), the gibbous moon (the first →→ of the full moon or the hope (fifteenth and sixteenth), the → gibbous moon (the first day of the first month→ the second quarter moon (the twenty-second and twenty-third) → the lower → new moon (the first day of the new month). The moon revolves around the earth, and the time interval between the moon phase and the next new moon, that is, the cycle of moon phase change, is called the synodic month.
Now that we know how the moon changes, let's take a look at how the moon goes. On Earth, we can see that the moon, like the sun, rises in the east and sets in the west every day.
On the first day of the lunar month, because the moon is away from the sun, we can't see the moon on the earth, but on this day the moon must be on the side of the sun, both rise and set at the same time, and it is possible to see its existence only during the solar eclipse.
After the new moon, about a day or two, the difference between the sun and the moon and the yellow longitude slowly increases, and the moon revolves around the earth from west to east, at this time the moon runs to the east of the sun, and the moon is illuminated by the sun for half a moon facing west, and the sun rises and sets at the same time, so the moon cannot be seen during the day, and only after sunset, we can see a curved moth moon in the low sky in the west.
On the seventh and eighth days of the first lunar month, when the difference between the ecliptic longitude of the sun and the moon reaches 90°, the moon continues to orbit the earth to the east, and the moon-earth line is 90° with the sun-earth line, and the sun has just set in the west, and we can see the semicircular first quarter moon in the southern sky. The further the sun sets, the moon will also go down, and in the middle of the night, when the sun goes below the horizon, the moon will disappear from the western horizon.
Therefore, we can only see the first quarter moon in the first half of the first half of the month, and the moon illuminated by the sun faces west and is located in the western sky, so the mantra summarized by people is called "go up and go up to the west".
Around the eleventh and twelfth of the lunar month, the difference between the sun and the moon continues to expand, and when the sun sets in the west, a fat waxing gibbous moon (more than half of the part illuminated by the sun) will appear in the southeastern sky, and then continue westward, and disappear from the western horizon before dawn.
On the fifteenth and sixteenth day of the lunar calendar, when the difference between the sun and the moon and the yellow longitude is 180 °, the moon is just opposite the sun, because of the existence of yellow and white angles, the earth can not block the daylight, when the sun sets in the evening, we can see a full moon rising from the eastern horizon, located in the south of the sky in the middle of the night, and falling from the western horizon in the early morning, and the bright moon can be seen in the sky all night. During a total solar eclipse, you may also have a chance to see a Blood Moon (Red Moon).
The ancients believed that the appearance of the blood moon was a great omen, which was completely superstitious. In fact, as long as the moon appears near the horizon, the thick atmosphere absorbs the light of other colors, and will refract the red light onto the surface of the moon, so the moonrise and moonset will appear blood-red like sunrise and sunset.
If we want to see the Blood Moon, we should remember that before the Full Moon it can only be seen at the time of the moonset, after the Full Moon it can only be seen at the time of the moonrise, and on the day of the Full Moon, it can be seen at the moonrise and moonset, that is, at sunrise and sunset.
But in order to really see the Blood Moon, you must seize the moment, due to the speed of the Moon and the influence of the thickness of the clouds, the Blood Moon will not last very long, as long as the Moon rises a little higher, it will immediately return to its bright "face".
After the full moon, about the eighteenth and nineteenth of the lunar calendar, the difference between the sun and the moon and the yellow longitude exceeds 180°, and after a period of dusk, the gibbous moon rises from the east, and at sunrise, the moon has not yet set, but it cannot be seen at dawn.
In a few days, on the 22nd and 23rd of the lunar calendar, the difference between the sun and the moon and the yellow longitude reaches 270°, and the line between the moon and the earth and the sun and the earth becomes 90°, and we can only see the moon rising from the eastern horizon in the middle of the night, hanging high in the southern sky at dawn, but it is invisible as soon as the day dawns, and it sets from the western horizon at noon, which is the second quarter moon corresponding to the first quarter moon.
Therefore, we can only see the last quarter moon in the second half of the second half of the moon, and the moon illuminated by the sun faces east and appears in the eastern sky, so the mantra is "go down and go down to the east".
On the 25th and 26th of the lunar calendar, the moon becomes more and more curved, and becomes the lower moth eyebrow moon corresponding to the beginning of the month, which rises after the middle of the night, is invisible at dawn, and sets at dusk.
In a few days, the difference between the sun and the moon and the yellow longitude will be 0° again, the sun and the moon will be conjunct again, and a new cycle will begin, and the moon will once again "secretly change its face".
Okay, so that's the magic moon phase change, have you learned it?
Reference: WeChat public account Guofeng student Mu Zixin
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