The nautical sextant has its roots in the 18th century, when it developed from other angle-measuring instruments such as the astrolabe and the quadrant. Since then, it has undergone improvements and adaptations to meet the needs of various fields, including astronomy.

Applications in astronomy and navigation

In astronomy, the sextant is essential for measuring the position of the stars in the sky, making it possible to draw up celestial maps and study the movement of the planets and stars. It is also used in geodesy and surveying to measure the height and distance of distant objects such as mountains or buildings form your sailboat. These applications make the nautical sextant an indispensable tool in old classic navigation.

Parts and function of the nautical sextant

A sextant is an instrument for measuring the angle between two objects. It is composed of several essential parts:

  • The frame and the limb are the main structure of the nautical sextant. The frame holds all the parts and the limbo is a graduated scale that allows angles up to 120 degrees to be measured.
  • The index and vernier are two sliding parts that allow for more precise measurement. The index is a movable arm that holds the mirror and the viewfinder, while the vernier is an auxiliary scale used to measure fractions of a degree.
  • The mirror and the viewfinder are essential components that allow angles to be measured without the need to look directly at the object. The mirror reflects the image of the celestial or terrestrial object to the viewfinder, located in the frame of the sextant.

The nautical sextant may also include additional items such as eye protection filters, adjustment screws and a bracket to hold the instrument.

Use and procedure

To measure the height of a star, the sextant is placed perpendicularly and oriented towards the horizon line. The star is then searched for through the telescopic sight by moving the movable mirror until it is found.

Once located, it is matched to the horizon reflection displayed in the middle of the fixed mirror. By means of slight oscillations of the nautical sextant, the image of the horizon is made tangent to the image of the star, which makes it possible to determine the angle measured at the limb. Subsequently, corrections are made to obtain the true height of the star.

Other applications and maintenance

In addition to navigation and astronomy, the nautical sextant is used in geodesy and surveying to measure heights and distances. To maintain its accuracy and proper functioning, it is important to perform proper maintenance, including regular cleaning and lubrication of the moving parts of the sextant and to store it in a dry and protected place. In the case of repairs, it is recommended that a specialist be consulted, although there are basic adjustments that can be made by following the instructions and having the right tools.

The nautical sextant is an instrument for measuring angles that has evolved over the centuries. Its accuracy and versatility make it invaluable in fields such as astronomy, navigation, geodesy and surveying. With its diverse applications and its ability to determine the position, height and distance of celestial and terrestrial objects, the nautical sextant continues to be an essential tool for professionals and enthusiasts exploring the world and the universe around us.

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