Sextant navigation tool

The sextant is a navigation instrument that measures angles between celestial bodies and the horizon, essential for celestial navigation since the 18th century.

About this subject

The sextant was independently invented by John Hadley in England and Thomas Godfrey in America around 1730, replacing the astrolabe and quadrant. It allows measuring angles up to 120 degrees, enabling precise determination of latitude and longitude by observing the Sun, Moon, or stars. Unlike the quadrant, the sextant uses a double mirror system that aligns the celestial body with the horizon, even with the ship's motion.

During the 18th and 19th centuries, the sextant was crucial for maritime exploration, including voyages by James Cook and Charles Darwin. Measurement accuracy depended on the navigator's skill and the instrument's quality, typically made of brass and glass. Variations included the pocket sextant and the aviation sextant, used in aircraft before GPS.

With the advent of GPS, sextant use declined, but it is still taught in navigation schools as a backup method and to preserve tradition. In electronic failures, a trained navigator can use a sextant to determine position within a few nautical miles. The instrument is also valued by collectors and history enthusiasts.

Interestingly, the name 'sextant' derives from Latin 'sextans', meaning one-sixth, referring to the 60-degree arc of its scale. While instruments with 45-degree (quintant) and 90-degree (octant) arcs exist, the 60-degree sextant became standard for its versatility. Today, replica sextants are used in films and exhibitions to recreate the age of exploration.

Frequently Asked Questions

How is a sextant used for navigation?

The navigator points the sextant at a celestial body, such as the Sun, and adjusts the arm until the reflected image touches the horizon. The reading on the arc gives the angle, which along with exact time and astronomical tables allows position calculation.

What is the difference between a sextant and an astrolabe?

The sextant is more precise and can measure larger angles, up to 120 degrees, while the astrolabe measures up to 90 degrees. The sextant is also more practical on ships as it compensates for motion.

Is the sextant still used today?

Yes, mainly as a backup in maritime and aviation navigation, and in navigation training. Many long-distance sailors carry a sextant for emergencies.