The concept and application of the sextant

2022-08-02
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Concept and application of sextant

sextant is an optical instrument used to measure the angle between two distant targets. It is usually used to measure the angle between the sun or other celestial bodies and the sea level or horizon at a certain time, so as to quickly know the longitude and latitude of the location of the ship or aircraft. The principle of sextant was first proposed by Newton. The sextant has a fan shape. Its components include a small telescope, a semi transparent fixed plane mirror, i.e. the horizon mirror, and a movable mirror associated with the index, i.e. the index mirror. The scale arc of the sextant is 1/6 of the circumference. When in use, the observer holds a sextant and rotates the indicator lens so that the celestial bodies appearing simultaneously in the field of view coincide with the sea level

according to the rotation angle of the index mirror, the altitude angle of the celestial body can be read out, and the error is about 02 ~ 1. In the field of view of the aviation sextant, there is a level that replaces the horizon. This sextant usually has a reading averaging mechanism. The sextant is characterized by its portability. It can be observed on a swinging object such as a ship. The disadvantage is that it cannot be used in rainy days. After the 1940s, although various radio positioning methods appeared, the sextant was still widely used

2. According to the wire diameter in the parameter table, the China Motor Products Circulation Association of Shanghai Municipal People's government selects the clip arc radius r

when early navigators navigated along the route in the sea, they need to constantly determine the position of the gb3142 (8) 2 ship, that is, the intersection of longitude and latitude. In order to find out the latitude of their ship, a navigator needs an instrument that can determine the latitude by measuring the angle between the horizon and the noon sun, or by measuring the angle between the horizon and a fixed star. At first, sailors used the astrolabe to measure the height of the sun, but because the ship's deck fluctuated up and down, this instrument was extremely difficult to operate and was not easy to measure accurately. Later, people replaced the astrolabe with a goniometer. Serious static electricity during navigation will also produce impact and even sparks. Sextants, bipedal compasses, protractors, parallel rulers and other early navigation instruments on charts

In 1731, Hadley invented the reflection quadrant and soon developed into a sextant, a bow instrument measuring 1/6 of the circumference. Hadley worked with Halley to develop a reflecting telescope. He then built an instrument for measuring angles at sea. The observer can see the horizon and the sun at the same time through a mirror, and the angle between them is measured with a quadrant marked on the edge. In 1732, the British Admiralty put a quadrant measuring the angle of 90 degrees on a speedboat for testing, and the results were very accurate. So quadrant became a necessary instrument for naval navigation. In 1757, Captain Campbell enlarged the quadrant radian to measure the included angle of 120 degrees. In this way, the quadrant became a sextant. It consists of a triangular frame, one side of which is an arc-shaped plate with a scale and a movable pointer. When the reflector reflects the two objects whose included angle needs to be measured together, it can easily measure the angle and calculate the latitude of the ship, so as to ensure that the ship travels along the correct route

France's large passenger ship France uses advanced electronic navigation instruments to control its automatic driving in bad weather. However, under special circumstances, sextant is still needed to assist in determining orientation

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