How was the theodolite invented? How to use it?

It was first developed by British mechanic Xisong in 1730, and was officially used in British geodesy after being improved and finalized. 1904, Germany began to produce glass dial theodolite. With the development of electronic technology, electronic theodolite appeared in 1960s. On this basis, an electronic rapid measuring instrument was manufactured in 1970s.

Theodolite consists of telescope, horizontal dial, vertical dial, level and base. When measuring, put the theodolite on a tripod, aim the center of the instrument at the ground station with a vertical ball or optical collimator, level the instrument with a level instrument, aim the measuring target with a telescope, and measure the horizontal angle and vertical angle with a level dial and a vertical dial. According to the accuracy, it is divided into precision theodolite and ordinary theodolite; According to the reading equipment can be divided into optical theodolite and vernier theodolite; According to the shafting structure, it can be divided into retest theodolite and direction theodolite. In addition, there is a coded dial theodolite, which can automatically record dial readings according to coded perforations; An automatic tracking theodolite that can continuously and automatically aim at air targets; Gyro theodolite and laser theodolite that can determine the orientation of ground points quickly and independently by using gyro orientation principle; Universal theodolite for astronomical observation with three functions: theodolite, meridian instrument and zenith instrument; Phototheodolite, who combined the camera and theodolite for ground photogrammetry. The original invention of theodolite was closely related to navigation. 15, 16 th century, some developed countries, such as Britain and France, needed to draw various maps and charts because of navigation and war. Triangulation is the earliest method used to draw maps, which is to find out the position of the third point in the distance according to the observation results of two known points. However, due to the lack of suitable instruments, limited means of angle measurement and low accuracy, the topographic map drawn is not high either. The invention of theodolite improves the observation accuracy of angle, simplifies the process of measurement and calculation, and provides more accurate data for drawing maps. Later, theodolite was widely used in various engineering surveys. Theodolite includes three parts: base, scale (horizontal scale and vertical scale) and sighting part. The base is used to support the whole instrument. The horizontal dial is used to measure the horizontal angle. The sighting department includes a telescope, a leveling tube and a reader.

Use of theodolite

Support the theodolite on a shelf, such as a chair or camera tripod, in order to make the line of sight easy to observe through the screw ring of D, and place the theodolite south. First, don't lift the sight arm D (that is, the latitude table E points to zero). Adjust the inclination of the B board so that the line of sight can see the horizon along the viewing arm. Fix the B plate in this position, and then keep the B plate horizontal. Now rotate c and d to observe the celestial body, and then e represents the height of the celestial body.

Now raise the theodolite to an angle x, where X = 90- (the latitude of the measuring place). For example, measured in Taipei, the latitude is about 25 3', and the angle X is equal to 64 57'; Another method is to aim the aiming arm at the north star, keep D in this direction, and move the A board to make the reading of latitude table E 90. At this time, board A and board B are at an angle of X. Of course, if you think about it a little, you can measure the latitude of your position in this way. Why is the angle between a and b x? (Note 1)

When you look up at the celestial pole (that is, at the North Star), the elevation angle is your latitude, so when the E reading is zero, lift the plate A by X angle, and the sight arm will point to the celestial equator. Why? (Note 2) The purpose of adjusting the X angle is to find the elevation angle of the star to the equatorial plane of the celestial sphere (that is, declination), regardless of the change of the apparent position of the star caused by the latitude of the observation point. At this time, the equatorial position of the celestial sphere is drawn by rotating the sight arm from west to east.

In order to measure the right ascension, the longitude table F must be carved into the right ascension unit hour. When the interval of 15 is 1, it must be carved counterclockwise from zero.

Now move the sight arm to see a known star in the southern sky, determine the right ascension and declination of this star from the star map, astronomical calendar or other reference star sources, and rotate the longitude table F to make the pointer of C point to the appropriate right ascension value. At this time, the latitude table should automatically indicate the correct declination value, otherwise the instrument will be biased. Fixed f, now rotate c and d, and point the aiming arm at another planet. At this point, we can read the declination and declination of the planet from E and F. The declination of the star north of the celestial equator is positive, and the declination of the star south of the celestial equator is negative, that is, the protractor at the opening on the E disk is positive and the other is negative.

For example, you can see Kikuchi in the night sky in April, May and June. Its declination (R.A.)= 13h23m37s, declination (D.) =-119. Now rotate the observation arm D and look at Xuanyuan XIV. At this time, we can read 12 06' on E and 10h07m on F, so we know that R.A.= 10h07m, D. = 12 06 of Xuanyuan XIV.

For another example, Sirius can be seen in the winter night sky.

R.A is about 6h44m, and d is about-16 40'. After adjusting F to 6h44m, raise the aiming arm at 25 declination position, and then rotate it to 3h45m declination position to the west. At this time, you can see the Pleiades through the spiral ring on D.

In early autumn and winter nights, near the Pegasus Plaza, you can see a hazy and bright light band. It is Andromeda, the only spiral nebula that can be clearly seen by the naked eye. Are you interested in finding its approximate location? It is about R.A.=0h40m, d. = 4 1.

The advantage of finding right ascension and declination by this method is that there is no need to worry about the factors that cause the apparent position change of the planet because of the different observation time. Why? Because disk A is coincident with the equatorial plane of the celestial sphere after X-angle correction, the elevation angle of the star to disk A (that is, the equatorial plane of the celestial sphere) obtained by E is naturally declination. Although the celestial sphere is constantly rotating, all the stars are almost distant stars, and their relative positions remain unchanged. We know the declination of a star. Based on this, we can naturally calculate the declination of another star from the angle between this star and other stars, so no matter what latitude, season and time you observe, the declination number and declination number of the star you get will not be different.

Table 2 lists some reference star sources.

For many great experiments, the equipment it needs is often quite simple. Don't underestimate the theodolite. It is very likely that one day, you will use it to locate a planet that has never been discovered before and become famous in the world.

The original text is taken from 1 17 "Project and Experiment", which was published in 1962 by the National Association of Science Teachers.

The original text only explains the production method and does not discuss the principle. The translator has made some simple explanations for this principle.

Note 1: As shown in Figure 4, plate B points to the southern horizon, plate D points to the north pole of the celestial sphere, and plate A is perpendicular to it. ∠Y is the latitude of the observation site. Because Polaris is far away from the earth, it points to the north pole of the celestial sphere and is parallel to the straight line from the north pole to the center of the earth. We can easily prove that ∠Z=∠Y and ∠ X+.

Note 2: When the reading of E is zero, D is parallel to A, as shown in Figure 4, A is at right angles to the celestial north pole, that is, it points to the celestial equator, so D also points to the celestial equator.