For as long as humans have lived on earth, they have invented ways to navigate it. For our earliest ancestors, travelling across land was normally a question of direction, weather conditions and availability of natural resources. However, navigating the vast sea has always proved more complex and dangerous, with errors in calculation leading to a lengthier voyage at best and disaster at worst.
Before the invention of scientific and mathematically-based navigational instruments, mariners relied upon the sun and stars to tell the time and determine where they were on the seemingly endless and featureless ocean. For centuries, celestial navigation helped guide sailors safely to their destinations, and the ability to do so became a highly-prized skill.
But where did celestial navigation originate, and why is it still sometimes used today?
The art of celestial navigation is 4,000 years old
The first Western civilisation known to have developed oceanic navigational techniques were the Phoenicians in around 2000 BC. They used primitive charts and observed the sun and stars to determine directions, and by the end of the millennium had a more precise handle on constellations, eclipses and moon movements which allowed for more safe and direct travel across the Mediterranean during both the day and night.
They also used sounding weights, which were lowered from a boat and helped sailors determine the depth of water and could indicate how close a ship was from land.
The ancient Greeks also likely used celestial navigation: a wreckage discovered in 1900 near the little island of Antikythera was home to a device known as the Antikythera mechanism. Made up of three corroded pieces of flat bronze and featuring many gears and wheels, it is thought to have been the world’s first ‘analogue computer’ and was possibly used as a navigational instrument that understood the movements of celestial bodies in the 3rd or 2nd century BC.
Developments were made during the ‘age of exploration’
By the 16th century, the ‘age of exploration’ had made great navigational sea-faring strides. In spite of this, it took centuries for global navigation at sea to be possible. Right up until the 15th century, mariners were essentially coastal navigators: sailing on the open sea was still limited to regions of predictable winds, tides and currents, or areas where there was a wide continental shelf to follow.
Accurately determining latitude (location on earth north to south) was one of the first early accomplishments of celestial navigation, and was reasonably easy to do in the northern hemisphere by using either the sun or stars. Angle-measuring instruments such as a mariner’s astrolabe measured the altitude of the sun at noon, with the angle in degrees corresponding to the latitude of the ship.
Other latitude-finding instruments included the horary quadrant, cross-staff and sextant, which served a similar purpose. By the end of the 1400s, latitude-measuring instruments had become increasingly accurate. However, it was still not possible to measure longitude (location on Earth west to east), meaning that explorers could never precisely know their position at sea.
Compasses and nautical charts helped with navigation
One of the earliest man-made tools to aid navigation was the mariner’s compass, which was an early form of the magnetic compass. However, early mariners often thought their compasses were inaccurate because they didn’t understand the concept of magnetic variation, which is the angle between true geographic north and magnetic north. Instead, primitive compasses were mainly used to help identify the direction the wind was blowing from when the sun was not visible.
During the mid-13th century, mariners recognised the value of plotting maps and nautical charts as a way of keeping a record of their voyages. Though early charts were not hugely accurate, they were considered to be valuable and as such were often kept secret from other mariners. Latitude and longitude were not labelled. However, between major ports, there was a ‘compass rose’ which indicated the direction to travel.
‘Dead reckoning’ was also used by ancient mariners, and is considered to be a last-resort technique today. The method required the navigator to make meticulous observations and keep meticulous notes that factored in elements such as compass direction, speed and currents to determine the ship’s location. To get it wrong could spell disaster.
‘Lunar distances’ were used for timekeeping
The first theory of ‘lunar distances’ or ‘lunars’, an early method of determining an accurate time at sea before the invention of precise timekeeping and satellite, was published in 1524. The angular distance between the moon and another celestial body or bodies allowed the navigator to calculate latitude and longitude, which was a key step in determining Greenwich time.
The method of lunar distances was extensively used until reliable marine chronometers became available in the 18th century and affordable from around 1850 onwards. It was also used way up to the beginning of the 20th century on smaller ships that couldn’t afford a chronometer, or had to rely on the technique if the chronometer was faulty.
Though lunar distances are normally only calculated by hobbyists today, the method has experienced a re-emergence on celestial navigation courses to reduce total dependence on global navigation satellite systems (GNSS).
Today, celestial navigation is a last resort
Celestial navigation is still used by private yachts-people, particularly by cruising yachts which cover long distances around the world. Knowledge of celestial navigation is also considered to be an essential skill if venturing beyond the visual range of land, since satellite navigation technology can occasionally fail.
Today, computers, satellites and the global positioning system (GPS) have revolutionised modern navigation, allowing people to sail across vast swathes of ocean, fly to the other side of the world and even explore space.
The advances of modern technology are also reflected in the modern role of the navigator at sea, who, rather than standing on deck and gazing at the sun and stars, is now normally found below deck.