The principle of the sextant and how to use the sextant

The angle of reflection of the ray rays is equal to the angle of incidence.

The principle on which the sextant is based is simple: the angle of reflection of the light is equal to the angle of incidence. In fact, a sextant can also measure the angle between any two objects.

Its principle was first proposed by Newton (and earlier Hooke); The fixed large sextants were built by major observatories for astrometric measurements very early (e.g., the chronometer built by Tycho on Boon Island, the large sextant of the Greenwich Observatory, etc.).

The sextant for navigation is a handle on the back of the fan-shaped frame for holding, and the frame is equipped with a movable arm, and the top end of the movable arm in the figure is the indicator mirror; The semi-reflective horizon mirror is mounted on the left side of the sextant (center, facing the telescope), and there is a filter next to the horizon mirror for measuring bright objects such as the sun. When measuring the horizon height of a celestial body, the observer holds a sextant to keep the telescope tube horizontal, and observes the image of the measured celestial body reflected by the horizon mirror from the telescope. At the same time, adjust the movable arm so that the star falls on the horizon as seen in the telescope. This is also the reason why horizon mirrors need to be made of semi-reflective glass.

The Law of Reflection in Geometrical Optics.

When the image of a celestial body coincides with the horizon, the height of the celestial body is equal to twice the angle between the horizon mirror and the indicator mirror. This can be easily demonstrated by the law of reflection in geometrical optics. Properly designing the scale on the arc scale based on this will allow the observer to read the celestial altitude directly.

In order to improve the accuracy of the reading, the actual sextant arm is often accompanied by a drum wheel and vernier ruler. The accuracy of the sextant is relatively high, up to 10 arc seconds, and it is light and easy to use, so it can quickly replace the previous complex operation of the astrolabe, become a sharp tool for measuring geographical coordinates on the ocean, and completely solve the problem of accurately determining the sea route that has plagued countless navigators. In 1769, Captain Cook successfully arrived in Tahiti with the help of a sextant to observe the transit of Venus.

High-tech instrument sextant, using the principle of objects at different angles of space and horizon!

The observer holds a sextant and rotates the index mirror car to read the altitude angle of the celestial body.

2.Then read the horizon height of a celestial body when it is in the middle of the sky.

3.Then consult the astronomical almanac to find out the equatorial coordinates of the object on that day.

4.Then substitute the formula: "cos z = sin sin δ cos cos δ cos t degree", 5Corrections are then made from the data published in the astronomical almanac.

Note: where z is the zenith distance of the celestial body (90 degrees minus the horizon height), δ is the declination of the celestial body, and t is the time angle.

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Basic DefinitionIt is used to measure the horizontal angle of a ground target and the vertical angle of the height of a celestial body. It is mainly used for nautical positioning and coastal bathymetric positioning.

The space sextant consists of two telescopes, an angle measuring head, a reference platform and a computing device. The angle measuring head is mounted on a frame with 3 degrees of freedom, and on the platform is mounted a plane mirror, prism assembly, and a gyro assembly, which measures the angle between the bright edge of the moon and the bright star. When the angle between the first star and the center of the Moon is measured, the spacecraft is somewhere on the cone, the apex of this cone is at the center of the Moon, and the axis of the cone is in the direction of the star.

A second measurement of another star and the moon establishes another cone. The spacecraft is located on two intersecting lines of two cones, one of which is fake, and its authenticity can be identified based on the physical characteristics of the spacecraft's flight.

The attitude of a spacecraft is determined by measuring the angle between two or more stars and a reference mirror fixed to the base of the sextant. The light source housed in the telescope is automatically aligned with the reference mirror and thus serves as a reference for the telescope. The angle relative to the reference mirror determines one direction of the inertial space, and the other attitude direction is determined by measuring the angle between one or several stars and the prismatic assembly.

The prism assembly is mounted on a reference mirror and has an elevation angle to the mirror. The two measurements are processed by the processor to obtain accurate attitude information.

This space sextant was developed by the US Air Force from 1973, from 1975 to 1978 to complete the development of engineering model hardware, in 1982 through the space shuttle flight experiments, in the late 80s of the 20th century officially provided for use. Based on the results of flight experiments conducted on the Space Shuttle, the Space Sextant can provide measurements of both orbit and attitude. The track position accuracy is 240 m, and the velocity accuracy is o 03 m s.

These precisions are related to the height of the track, and the lower the orbital height, the higher the speed accuracy. The three-axis attitude accuracy is 1" (angle). The space sextant has a mass of 25 kg, a power consumption of 50 W, and a design life of 5 years.