What is the function of the armillary sphere?

As can be seen from the notes of the armillary sphere, the small armillary sphere is a wooden ball smaller than the armillary sphere. First draw a great circle on the spherical surface as the equator, then draw a great circle with a 24-degree angle as the ecliptic, and divide it into 365 scales on the yellow equator, both of which start from the winter solstice. At the equatorial North Pole and its collision site (namely the South Pole), each needle uses a hole as the two ends of the sphere's rotation axis. Take a long bamboo stick and make a hole in the center of both ends, so that the distance between the two holes is equal to the length of half a big arc of the ball. Overlap the two holes of the bamboo stick with the north and south poles, and the bamboo stick runs through the ball. At this time, the connecting line between the two holes of the bamboo stick must be consistent with the ball, because the distance from the north pole to the south pole pinhole center is exactly equal to 182 5. Cut off half a bamboo stick along the middle line, so that the middle line is just the connecting line of the holes at both ends of the bamboo stick. Starting from the winter solstice, move the center line of the bamboo pole every other degree along the equator, and read the degree of its intersection with the ecliptic every time, so that every time the equator increases by one degree, the degree of the ecliptic is more or less. This number is the number of times the yellow equator advances and retreats. When the increase rate of equatorial degree is greater than that of ecliptic degree, it is multiple and progressive; ; On the contrary, less is counting backwards. This is the earliest and most detailed record of the specific method for measuring the advance and retreat of the Yellow Equator in ancient China. After the small armillary sphere model is made, it is accurate as an experiment, and then it is cast into a formal instrument with copper. Under the careful operation of Zhang Heng, it took a lot of effort. After more than a year's efforts, this instrument was finally made successfully. Because this musical instrument is made according to the theory of Huntian, Zhang Heng named the model made of bamboo "Little Huntian Instrument" and the model made of copper "Huntian Instrument". Zhang Heng's astrolabe is similar to the modern fake astrolabe in many places, but the modern fake astrolabe is certainly much more accurate than it. Zhang Heng's armillary sphere is made according to the principle of armillary sphere. Its shape is a spherical thing, equivalent to the current celestial globe. The armillary sphere is divided into inner and outer layers, each layer can rotate, and an iron shaft runs through the center of the sphere in the middle. The direction of the axis is the direction of the earth's rotation, and the contact between the axis and the sphere has two intersections, namely the North Pole and the South Pole on the celestial sphere. Half of the ball is hidden below the horizon and the other half is exposed above the horizon. There are 28 constellations and other stars on the sphere, and there are ecliptic circle and equatorial circle on the sphere, which form an included angle of 24 degrees and have 24 solar terms respectively. From the perspective of winter solstice (winter solstice is the beginning of a year in ancient times), the circle is divided into 365 degrees, and each degree is subdivided into four compartments. There are two circles outside the sphere, one is the horizon and the other is the meridian circle. The circumference of the outer circle is one foot, four feet and six inches. The celestial axis is supported on the meridian ring at an oblique angle of 36 degrees from the horizon, which means that the North Pole is 36 degrees higher than the horizon. This is the elevation angle of the North Pole of Luoyang and the geographical latitude of Luoyang. The structure of this instrument contains almost all the advanced astronomical knowledge at that time. In order to make the armillary sphere rotate by itself according to time, Zhang Heng designed a set of leaky cans. The leaky drip pot is an ancient timekeeping tool. It uses a special water container with a small hole at the bottom, and the water drops into the pot engraved with time marks. People can know what time it is just by looking at the water depth in the pot. The clock was not invented at that time, so our ancestors used it to time. Zhang Heng used this principle to design a set of drippers, skillfully used two pots to cooperate with the armillary sphere, and used the power of dripping water in the pots to drive the gears, thus driving the armillary sphere to run. By properly selecting the number of gears, the armillary sphere skillfully rotates day and night, vividly demonstrating the changes of the astronomical phenomena, and people can observe the phenomenon that the sun, the moon and the stars run from the armillary sphere. After Zhang Heng made the bronze armillary sphere, he installed it in a secret room and turned it with the power of running water. Then, let a manager close the room and report loudly to the observer standing on the observation platform: which star on the armillary sphere is rising, which star is reaching the zenith and which star is falling. Everything is in perfect harmony with the sky. In addition to armillary sphere and broken kettle wine, Zhang Heng also created a mechanical calendar called "Ruilun Ghost Pod". The Book of Jin Tian Wenzhi records: "When Shun Di arrived, Zhang Heng made another elephant ... and turned it into a room in a temple through water leakage. The existence of stars corresponds to the sky. Because of his embarrassment, he turned to the auspicious wheel and ghost pod under the steps, and the moon was full and started to fall according to the calendar. " Ghost pod is a legendary tree. It lays a pod every day. After pod 15, one pod is dropped every day and then grows again. Inspired by this, Zhang Heng created Ruilun Ghost Pod, which is equipped with a mechanism. Fifteen dials with cam function are installed on a vertical shaft, so that they can act on the fifteen ghost pods in turn, each rising and falling at an appropriate time. Then put the Ruilun ghost pod next to the terrace outside the armillary sphere hall. Connected to the drip pot, it is also connected to the armillary sphere by leakage. From the beginning of each month, one piece of konoha leaves will be transferred out every day, and 15 will be transferred out on the day of 15 * *, and then another piece will be transferred every day, which will be reduced in turn until the moon sets. Because the lunar calendar is in harmony with the movement of the moon, this instrument can not only display the date, but also show the increase and decrease of the moon round by round, that is, it rotates and opens again and again according to the order of the new moon, winding, looking at the sun, winding and dark day in the lunar calendar, so that people can get the effect similar to the activity calendar from the Swiss wheel.