Chapter 9 Section 2 Observation Instruments

A gauge is a device for studying the orientation of the sun.Another type of instrument can be used to study the laws of motion of almost all celestial bodies including stars and planets, including the sun and the moon. This is instrument and image. "Yi" refers to an instrument for measuring the position of celestial bodies, and "Xiang" refers to an instrument for demonstrating the apparent movement of celestial bodies, collectively called Yixiang.The armillary sky theory is the dominant cosmology in ancient China, and the armillary sphere and armillary phase are the observation instruments to explain the armillary sky theory.

It is speculated that the origin of the armillary sphere predates the Western Han Dynasty.However, as far as we know now, the detailed structure of the armillary sphere was not recorded for the first time until "Sui Shu Astronomical Records".The Kongting armillary sphere is composed of four rings and one tube: the equator ring is parallel to the celestial equator, the horizon ring is parallel to the ground plane, and the meridian ring connects the north and south celestial poles. These three rings are fixed.The four-way ring, which is equivalent to the right ascension ring, is movable and can rotate around the polar axis that runs through the north and south celestial poles.On the same plane as the four-way ring is a square cylindrical tube for observation, called "balance", also known as "peeping tube". The peeping tube is also movable and can rotate around the center of the four-way ring.The structural principle is very clear, the speculative tube can participate in two mutually perpendicular movements at the same time, the direction of right ascension and the direction of declination, which shows that the speculative tube can be aimed at any celestial body on the celestial sphere.Therefore, the depolarization of a celestial body can be directly read from the four-way ring, and the degree of entry of a celestial body is equal to the difference in right ascension between the celestial body and the first star to the west of it.In addition to the equatorial coordinates, the Kongting armillary sphere also has a horizontal coordinate system.It should be noted that the scale on the equatorial ring is not the modern 360 equal division, but 365.25, that is, 365 divisions plus 1/4 division.This tradition of incomplete points has made many people strange and puzzled. In fact, it has a history.Ancient astronomers used standard scales to measure the distance from the winter solstice to the next winter solstice, record it for several years, and take the average to get the length of the tropical year (called Suishi in ancient times).The length of the year of return determined during the Spring and Autumn and Warring States Periods is exactly 365.25 days. If the circle is divided by this number, the sun will move one space a day, which is exactly a full circle in a year, which shows its intention.After the Qin Dynasty, until the introduction of Western astronomy, the equatorial circle equal to 365.25 degrees was preserved as a tradition, although the length of the tropical year was continuously improved and kept accurate.In order to distinguish it from the traditional Chinese "degree", this book does not use "degree" when encountering the western angle unit "°".

Li Chunfeng, an astronomer in the Tang Dynasty, designed and manufactured a more complex armillary sphere in the early years of Zhenguan (630 A.D.), called the armillary zodiac instrument.The outer layer of the armillary zodiac sphere has a horizon ring, a meridian ring and an equatorial ring, which are all fixedly connected to the base of the instrument, which is called a sextile.The inner layer is a four-way ring and a peeping tube, called a four-way instrument.There are three rings on the middle layer - the zodiac ring, the equator ring and the white dao ring, which were created by Li Chunfeng himself.In ancient times, the sun, moon and stars were collectively called Sanchen, hence the name Sanchenyi.The four-way instrument can be rotated in the three-star instrument, and the three-star instrument can be rotated in the sextant instrument. The whole instrument has as many as seven rings, and has three coordinate systems of the equator, the ecliptic, and the horizon.The main advantages of armillary ecliptic instruments are: a. It can directly read out the celestial body’s occlusal degree without having to subtract the equatorial reading of the distance from the star; b. It distinguishes the orbit of the moon (white track) from the track of the sun (ecliptic) for the first time , can directly measure the position of the moon on the white path.Although the Moonny Sky Zodiac Instrument has been idle in the palace and has not been put into use, it has become a model for later generations because of its complete functions.

During the Northern Song Dynasty, there were many armillary spheres with fine craftsmanship, and the observation accuracy was deliberately improved.For example, improving the spy tube, correcting the polar axis, and paying attention to the installation of instruments, etc., drove astronomical research in the Song Dynasty to an unprecedentedly high level.Because the rings overlapped and staggered, causing many blind spots for the spy tube, and because the position of the moon can be read through equatorial coordinates or ecliptic coordinates, most armillary spheres in the Song Dynasty canceled the white rings and simplified the structure.After the Song Dynasty moved to the south, all the excellent instruments of the Northern Song Dynasty were moved to Yanjing (now Beijing) by the people of the Jin Dynasty.The few surviving pieces from the early Ming Dynasty were moved to Yingtianfu (now Nanjing) together with other Yuan Dynasty astronomical instruments.Later, when Emperor Chengzu of the Ming Dynasty moved his capital, he copied the whole set at a ratio of 1:1.Now, a Song Dynasty armillary sphere (see Figure 8), which was imitated in the fourth year of Ming Zhengtong (AD 1439), is still well preserved on the Zijin Mountain Observatory in Nanjing. The original Song Dynasty armillary sphere has been destroyed.

If you want to increase the observation function of the armillary sphere, you need to add rings appropriately. However, too many rings will bring a lot of inconvenience to the observation. This is a contradiction that is not easy to solve.After Li Chunfeng, the armillary sphere manufacturers of all dynasties made many attempts, such as reducing the ring, or shifting, or replacing, but they never got the most satisfactory idea.

It was not until the Yuan Dynasty to the thirteenth year of the Yuan Dynasty (1276 A.D.) that Guo Shoujing designed the Jianyi, which liberated the armillary sphere from the complicated structure of rings and rings.Jianyi is actually composed of two sets of independent instruments: 1. Four-way instrument 2. Axis 3. North celestial pole 4. Tianyuan meridian, namely the equatorial theodolite and the horizon theodolite.The equatorial theodolite not only gave up the white track ring, but also the ecliptic ring, and only kept the equatorial ring, horizon ring and four-way ring in the original armillary sphere, and the equatorial ring and the horizon ring no longer serve as the outer structure supporting the four-way ring, but It was moved to the southern end of the four-way ring, so that above the four-way ring, there is no other shelter except for a pole-receiving ring near the north celestial pole for correcting the polar axis.The horizon theodolite, also known as the Liyun instrument at that time, includes the Yin latitude ring and the Liyun ring.The female latitude ring is equivalent to the horizon ring, which is fixed.The Liyun ring is equivalent to the four-way ring, which can rotate around an axis perpendicular to the female latitude ring and passing through its center.Liyunyi is the first astronomical instrument in China that can simultaneously measure azimuth and horizon height.Although the armillary spheres in the past had horizon rings, they all lacked a ring that could rotate around the zenith, and without such a ring, the horizon coordinates could not be indicated.Another achievement of Jian Yi is to improve the accuracy of scale division.Before the Yuan Dynasty, the minimum scale of the instrument was 1/4 degree, but the simple instrument was 1/10 degree, and the estimated reading could reach 1/20 degree.

The original Jianyi was destroyed in the early Qing Dynasty, and there are only imitations in the fourth year of Ming Zhengtong (AD 1439), which are also in Nanjing Zijinshan Observatory.Under Jian Yi, Guo Shoujing's positive plan for correcting the direction should have been installed, but the imitation converted it into a sundial. Another invention of Guo Shoujing in the instrument is the Yangyi.The elevation instrument is specially used to measure the right ascension and declination of the sun.The armillary sphere cannot directly measure the position of the sun, because the glare of the sun makes it difficult for the speculum to aim at the center of the sun.The structure of the elevation instrument is relatively simple. It is a copper hollow hemisphere with an upward opening, and the equatorial coordinate network is engraved on the inside. The sun is imaged on the inside through a small hole, and the right ascension and declination of the sun can be seen at a glance.The appearance of Yangyi is different from traditional Chinese astronomical instruments, and it is unique.

Generally speaking, the design level of the armillary sphere has reached its peak in Guo Shoujing's era, whether it is the rationality of the layout or the perfection of details. After Guo Shoujing, there is no surpassing. The basic structure of the muddy image is a sphere on which the stars, horizon, ecliptic and equatorial circles visible all day long are marked on the sphere.As a demonstration instrument, the sphere can rotate around the polar axis connecting the South Pole and the North Pole. There are also active signs of the sun, moon and the five planets of Venus, Jupiter, Water, Fire and Saturn, which can be easily moved to simulate actual celestial phenomena.The muddy image is equivalent to the current celestial globe.

For astronomers, the muddy phase is mainly used for the conversion between ecliptic degrees and equatorial degrees.In modern astronomy, spherical trigonometry can easily solve the conversion problem of different coordinate systems.However, in ancient times when mathematics was not well developed, we had to adopt a clumsy method: use the right ascension circle to divide the equatorial circle and the ecliptic circle into several arc segments, and then compare and compare the yellow and red arc segments of the same right ascension, and compare them in pairs. Subtraction, a difference table can be listed, and then the continuous difference table can be obtained by interpolation.That is to say, whether the ecliptic degree is converted into equatorial degree or the equatorial degree is converted into ecliptic degree, check the continuous yellow-red difference table, or add or subtract, that is what you want.

Zhang Heng, an astronomer in the Eastern Han Dynasty, in order to prove the correctness of his cosmology (that is, the theory of the armillary sky), once designed and manufactured an armillary sphere called the Leaking Water Turning Armillary Sphere.The instrument is powered by the clepsydra flowing water, and drives the muddy image to rotate evenly through the gear system.After adjustment and proofreading, it can make it exactly one revolution a day and automatically match the astronomical phenomena. The leaky armillary sphere had a great influence on the design of the later generations. Many astronomers in the Tang and Song dynasties contributed to the improvement of Zhang Heng's work.Among them, the most worth mentioning is the Yuanyou armillary sphere, also known as the water transport sphere, made by Su Song and Han Gonglian in the Northern Song Dynasty.The observatory consists of three parts: the armillary sphere, the armillary sphere and the time telling system, which are respectively placed on the top, middle and bottom of the three-story wooden structure building, like a small observatory.The three parts share a set of transmission device and clepsydra, which can keep in sync with the apparent weekly motion of celestial bodies during operation.The amazing timekeeping system not only rings the bell every day, but also beats the drum when there is a carve. There is also a wooden man who presses the clock and beats the gong (zheng) at night. There is no doubt that its structure is very complicated.The research found that there is an escapement-like mechanism in the timekeeping system, and the escapement is an important part of modern mechanical clocks.After the completion of the water transport instrument platform, Su Song wrote an instrument manual "Xin Yi Xiang Fa Yao", which described in detail the shape, size, material and overall structure of each component. In particular, there are a large number of mechanical drawings in the book. , so that future generations of readers can peek into the details of the mystery.

Su Song and Han Gonglian also built a Hun Xiang that can be viewed from inside.According to the "Jade Sea" written by Wang Yinglin in the Song Dynasty, the muddy image is a hollow spherical shell, the diameter of which exceeds the length of a person's body, and the small holes pierced on the spherical surface represent stars.As the spherical shell rotates from left to right, the dots of light passing through the small holes are like the real starry sky at night, and the scene is very realistic, which is similar to the planetarium in the modern planetarium (see Figure 9). Since Zhang Heng, most of the instruments that need to be rotated are driven by a clepsydra. This is relatively easy to understand, because under the conditions at that time, it was impossible to find a more stable power than the clepsydra.It is only natural to ask whether the rotation of the instrument depends solely on the clepsydra.We know that the water volume of the clepsydra is very small, and the pressure it produces is extremely limited. It is hard to imagine that it can drive the copper eclipse, and the above-mentioned Susong Water Transport Observatory is even more difficult to drive. "Sui Shu·Geng Xun Biography" writes: "Xun creatively created the muddy sky without manpower, turned it with water, and put it in a dark (an dark) room." It shows that Geng Xun's armillary sphere was driven by water without manpower This seems to mean that Geng Xun's previous water transportation was not only based on water power, but also manpower.However, since there is manpower, why do we need water power, what is called "water transportation".The ancients seldom recorded the details of this aspect, and we have no way of knowing the real situation.Perhaps interested readers are willing to find the answer to it.