Man looking into a sextant with the sea in the background

Traditional maritime navigation: the Sextant in the GPS era

Are traditional maritime navigation methods a thing of the past or are they still useful in the satellite era?

In the era of satellite navigation systems, it might seem like traditional methods of orientation at sea are becoming obsolete. However, even in an age where satellite information is a standard part of our daily lives, traditional marine navigation using celestial bodies remains relevant and fascinating. Modern technology offers mariners precise information about their location, but understanding age-old navigation techniques becomes invaluable when electronic equipment fails or you lose the satellite signal.

History of sea navigation and the invention of the sextant

Since ancient times, navigation at sea has been a cornerstone of maritime exploration, with mariners using the sun and stars to guide their way. During the day, they oriented their voyage according to the sun, while at night the star Polaris served as a reference point. However, the accuracy of these methods was limited, and as technology advanced, more sophisticated instruments and navigation techniques were developed.

Compass, astronavigation and the sextant

Historically, navigating the treacherous waters of the Atlantic presented formidable challenges to seafarers, who depended largely on the compass and the estimated speed of their ship. Such methods, however, were fraught with limitations, often compromised by the unpredictability of sea currents or miscalculations in speed. The advent of astronavigation marked a significant leap forward in navigation techniques. By the 15th and 16th centuries, navigators were achieving positioning accuracy within ten kilometres, a feat made possible through meticulous celestial measurements and calculations. A further breakthrough occurred in the 18th century with the introduction of the sextant. This instrument allowed for unprecedented precision in measuring the altitude of celestial bodies above the horizon. Thanks to the sextant, mariners could ascertain their location with remarkable precision, narrowing down their position to within a nautical mile

navigator with sextant on watch on a naval vessel

Modern sextant in practice

How did the name for the sextant come about?

The "sextant" gets its name from "sextans," a Latin word meaning "sixth," reflecting its capacity to measure up to 60 degrees, or one sixth of a circle. This naming stems from the sextant's design, featuring a sixth of a circle arc divided into 60-degree segments, alongside a mirror for angle measurement.

The versatility of the sextant

The main advantage of the sextant is the ability to measure the height of the Sun, Moon or stars above the horizon with accuracy and reliability, allowing the position of the ship to be determined with minimal error. With mirrors and binoculars, the sextant allows sailors to measure angles even when looking at the horizon, which is crucial for measurement accuracy. Its compact size and ease of use make it an invaluable tool for any maritime expedition.

The Sextant is also advantageous in that it requires no external power source or electronic components, making it a reliable tool for use even in extreme conditions at sea. Thanks to its versatility and reliability, the sextant has become an indispensable part of every mariner's arsenal, leading to safer and more successful maritime navigation.

YACHTING.COM TIP: Find out what other inventions are used at sea in our guide to navigational aids on a yacht.  Also discover how to read nautical charts

Sextant: an indispensable tool for maritime expeditions

The sextant has been pivotal in naval history for pinpointing ships' positions at sea. Notably, during the American Civil War, British Admiral Sir George Cockburn, overseeing the blockade of the American coast at the turn of the 19th and 20th centuries, used the sextant to precisely locate his fleet, effectively blockading American ports and cutting off supply routes.

Another notable figure, British Captain James Cook, in the 18th century, was the first British captain to utilize the sextant on his exploration voyages. Cook's use of the sextant for mapping unknown parts of the globe was instrumental in discovering new islands and coastlines, creating important navigational charts for future generations of seafarers.

These examples highlight the sextant's critical role in the success and safety of maritime expeditions throughout history. Its reliability and accuracy, combined with the skills of experienced mariners, make it an invaluable tool for maritime navigation to this day.

YACHTING.COM TIP: In addition to navigation, it is also handy to know how to judge distance at sea when in the vast ocean.

Construction of the sextant

  1. Arc: The arc is the sextant's main component, crafted from metal or plastic, spanning roughly 1/6 of a full circle to measure up to 60 degrees.
  2. Mirrors: Integral to the sextant, two mirrors are positioned at the arc's extremities—one fixed, the other adjustable via a micrometer screw for precise alignment.
  3. Finder: Attached to the sextant, the finder aids in locating celestial bodies for navigation.
  4. Micrometer Screw: This feature facilitates the fine adjustment of the movable mirror, crucial for the accurate measurement of angles.
  5. Scale: The sextant includes a scale, marked in degrees and minutes, enabling the direct reading of angular measurements.
old naval sextant with optics on white background

Historical sextant

How to use a sextant: step by step

  1. Setting up the sextant: First, make sure the sextant is properly set up and calibrated. Check that the mirror is clean and sharp and that the sextant is balanced horizontally.
  2. Select the target: Choose the celestial body you want to use to determine your position. Common choices are the sun, moon, planets or stars.
  3. Target focus: Use the sextant to aim the selected celestial body so that its reflection from the horizon is reflected on the sextant mirror.
  4. Angle measurement: Using the measuring stage on the sextant, determine the angle between the selected celestial body and the horizon.
  5. Record the angle: Record the measured angle on the sextant's measuring scale.
  6. Calculate your position: Use the measured angle, the current date and time to calculate your position using nautical tables or special computer programs.
  7. Repeat for other points: Repeat this procedure for other celestial bodies to determine your position as accurately as possible.
  8. Interpret the results.
  9. Adjusting your route: Based on your position and other factors such as wind speed and direction, adjust your route to be safe and efficient.
  10. Thorough Maintenance: When you are finished using the sextant, clean it thoroughly and store it in a safe place so it is ready for future use.

YACHTING.COM TIP: In addition to the more traditional aids, we also have a rundown of the 10 best smartphone apps for sailors 

Modern use of the sextant

In the past, the sextant was an essential tool for navigation at sea, but with the advent of GPS satellite navigation, it is gradually losing its relevance. Back at the turn of the millennium, astronavigation was still common practice, but today we are increasingly relying on modern technology. Even so, knowledge of astronavigation remains important, especially as a backup plan in the event of electronic equipment failure or satellite signal failure. Although sextants are now rarely used on large ships, they remain on board. However, by combining traditional methods with modern technology, the sextant can become a key element for safe and successful navigation even today.

Today, all boats use modern navigation. So don't be afraid to set sail, we can help find you the perfect boat