Sextant navigation tool

The sextant is a navigation instrument used to measure angles between celestial bodies and the horizon, essential during the Age of Discovery.

About this subject

The sextant was invented in the 18th century, replacing the astrolabe and quadrant. It allows sailors to determine latitude and longitude with high accuracy by measuring the angle of the Sun or stars above the horizon. Its mechanism uses mirrors to reflect the celestial body until it aligns with the horizon, giving the precise angle. The name derives from its 60-degree arc scale. During the Age of Discovery, captains like Cook and Magellan relied on the sextant to chart unknown oceans. Even with GPS, the sextant remains a backup tool on ships and aircraft, taught in navigation schools. Besides nautical use, it serves in amateur astronomy and exploration. Typically made of brass or aluminum, it includes a telescope, mirrors, and solar filters. A skilled user can achieve positional errors under 0.1 nautical miles. The sextant symbolizes human ingenuity and the shift from empirical to scientific navigation.

Frequently Asked Questions

How does a sextant determine latitude?

The sextant measures the altitude of the Sun at local noon or a star (like Polaris) above the horizon. Latitude is then calculated using that angle, adjusted with solar or stellar declination tables.

Is the sextant still used today?

Yes, while GPS is dominant, the sextant remains a backup tool on ships and aircraft since it does not rely on electronic signals, proving essential during modern system failures.

What is the difference between a sextant and an astrolabe?

The astrolabe is older (10th century) and less accurate, measuring angles directly with the eye. The sextant uses mirrors to align images, allowing precise readings even in motion at sea.