What is Sextant ?
Sextant is a navigational instrument used to measure the angle between two objects, typically the horizon and a celestial body such as the sun, moon, or stars.
It is an essential tool for celestial navigation, allowing sailors, aviators, and adventurers to determine their position on the Earth’s surface based on celestial observations. Sextants have been historically important for accurate navigation, especially during long sea voyages and explorations.
Key features and components of a sextant :
- Frame: The main body of the sextant is a metal or wooden frame with a sighting mechanism and an arc. The arc is usually one-sixth (60 degrees) of a circle.
- Index Mirror: A small mirror is mounted at the center of the frame. It is used to reflect the image of a celestial body down to the user’s eye.
- Horizon Mirror: A larger mirror is placed at a 45-degree angle to the index mirror. It reflects the image of the horizon into the line of sight.
- Alidade and Vernier Scale: The alidade is a movable arm with a vernier scale that allows precise measurement of the angle between the two mirrors.
Using a sextant involves the following steps:
The user aligns the sextant so that the index mirror reflects the image of a celestial body (e.g., the sun) and the horizon mirror reflects the image of the horizon.
By adjusting the alidade, the user brings the two reflected images into alignment. The angle between the two mirrors is read from the vernier scale.
The observed angle, along with the time of observation, is used to calculate the user’s latitude or longitude based on celestial navigation tables or formulas.
Sextants have been historically crucial for navigation, especially during the age of exploration and when traveling long distances at sea. They allowed navigators to determine their position even when land was not visible and other navigational aids were limited. While modern technology has largely replaced sextants with electronic navigation systems like GPS (Global Positioning System), sextants are still used by sailors, aviators, and enthusiasts for educational and traditional purposes.