Charting the Course - Navigation Through History

Astrolabe, an ancient navigation device that combined star maps, terrestrial maps and measurement devices. A muslim device from the 11th century | Image: WH_Pics, Shutterstock

We Are On The Map

With all due respect to the Israellites, it is relatively easy to navigate on land. The terrain is filled with landmarks: high mountains, rivers, land formation, prominent structures and even types of vegetation and animals that are typical of certain regions. All that you need to find your path is a map that displays the location of these landmarks with their drawings, or pre-agreed-upon symbols. And indeed, already at early stages of humanity people began to map their surroundings. The question of how early this occurred is under debate. Many researchers consider a mural discovered during the digging of Çatalhöyük site in Turkey as the earliest map in our possession. The mural, probably from the 7th millennium B.C., is probably a diagram of the houses in the village, but not everyone agrees that it is a map.  Similar conflicts exist regarding artifacts that are even more ancient, such as mammoth tusks that are 10,000 and even 20 thousand years old that the patterns engraved into them might be a symbolic representation of the geographic environment, a 16 thousand year old rock from Spain that allegedly describes hunting grounds in the region and additional artifacts.     

Some of the ancient maps that we know were not only used for navigation: maps from ancient Babylon and Egypt, for example, were used for drawing borders between agricultural plots and to calculate their size for tax purposes. But to orientate in the surroundings, a map is certainly an essential tool. If we want to walk from Athens to Sparta, for example, we should head out from Athens going northwest and after 25 kilometers, at Eleusis, turn west-southwest and walk for 50 kilometers along the shore, until reaching Isthmia. From there about one hundred kilometers southwest, until tripoly, and then another 50 kilometers south, until the gates of Sparta. Without a map it will be very difficult to plan the path and make the journey. 

However, a map alone will not suffice. We also have to know where we are, at which direction we are walking and the distance we traveled, or the rate at which we walk to calculate it. Without such measurements there are good chances that we become lost along the way, or that we will need aids such ase marked roads, signs or gracious shepherds to guide us. In Greece there are good chances to find all of these, but in other places and distant times – it was not always like this. 

Maps were not only used for orientation, but also to set borders and calculate taxes. A computer scan of a Babylonian stone plate from the 7th century B.C., engraved with a map of mesopotamia | Source: SHEILA TERRY / SCIENCE PHOTO LIBRARY

The most obvious landmark at our service is the sun. Even at very early stages of history people noticed that it shines every morning from roughly the same direction and sets every evening at roughly the opposite direction. These phenomena are also the namesake of the names east and west. But if you want to know the direction during the time between sunrise and sunset, it becomes more complicated. During the day the sun travels across the skies - or appears to for a watcher standing on earth, to be precise - in a course that is not straight, but curved, with a lean south if you are in the northern hemisphere, or north - in the southern hemisphere. Its precise course through the sky depends on the location of the observer and the season, so that to determine directions using the sun you should know roughly where you are on earth, the date and knowing the time of day could also be helpful. 

During night time you can locate north with relative ease using North Star, which appears to us as hanging above earth’s north pole - if there are no clouds, naturally, and as long as we are located in the northern hemisphere. You can also use the location of other stars, or prominent constellations, but these also change to the observer along the night and the year, and also according to the observer's location. Here as well, knowing your location and the time are important for orientation - there is no wonder that throughout history the fields of cartography and navigation went hand in hand with technologies such as time measurement.   

At night it is simple to find North Star - in the northern hemisphere. A diagram that portrays the location of North Star (Polaris) relative to Ursa Major and Ursa Minor | Illustration: Mykola Mazuryk, Shutterstock

Navigating On The Waves

On land, as previously stated, you can use the terrain and other landmarks, not to mention roads and signs. At sea such landmarks do not exist and when there is only water from horizon to horizon, it is very difficult to find your direction and maintain it, moreover when the weather is not welcoming. Nevertheless, marine travel could be faster and more efficient than traveling by land, mainly if the land is mountainous, or if you want to transport a large quantity of goods. And of course, it has no alternatives if you are living on an island and wish to trade - or fight - with residents of other islands or continents. 

Ancient Greek societies, such as the Minoan and Mycenae, were among the first to develop shipbuilding and means of navigation alongside them. In many cases navigation in ancient Greece was coastal: the ships sailed for the most part at a viewing distance from the shore, while navigators were sailors with sharp eyesight that learned to recognize prominent features on the shore from afar and use them to orientate. Navigation according to the sun and stars also developed gradually.. 

There is no wonder that the English term “navigation”, and parallel terms in many languages come from the proto-indo-european word Nauta - ship or boat. In the past the term served not only to describe the act of navigating but also the sailing itself, and still does at times in modern English. 

In another part of the world, Polynesians in the Pacific Ocean developed astonishingly sophisticated methods to cross the great vasts of the sea between islands and archipelagos. Hundreds of years prior to the christian count, navigators passed on from one generation to the next in depth knowledge regarding the characteristics of the sea in different regions, according to features such as wind, types of waves and currents. All of these were differently represented in unique maps that were made of thin and flexible sticks and sea shell or coral fragments that represented the islands. These maps, along with the high skill level of navigators, enabled the Polynesians to find their ways between islands that are hundreds and even thousands of kilometers apart. 

The Polynesians, as well as the Greek and other cultures, often used animals to find their way and knew when to sail after certain fish or seabirds. In certain places sailors also used birds that they brought with them. When far out at sea they would release the bird. If it flew back to the ship they would sail on. If not - they would follow it, as there is a good chance it found some place to land. Authors of the biblical story of Noah must have known this method. 

Navigating by deep familiarity with the features of the sea, such as waves, currents and wind. Stick maps made by natives of the Marshall Islands | Image:  LIBRARY OF CONGRESS, GEOGRAPHY AND MAP DIVISION / SCIENCE PHOTO LIBRARY

Crossing The Lines

Greek astronomer, Ptolemy (Claudius Ptolemy), who lived and practiced in Alexandria in the 2nd century B.C., is considered the greatest astronomer of the ancient time. More precisely, he is one of several astronomers that are commonly known as such. Much like other scholars of his time, Ptolemy did not limit himself to one specific discipline, probably for the better. His work in astronomy included detailed and thorough mapping of constellations, but also a false description of the solar system, based on the perception that the sun and other planets circumvent the earth, and also astrological studies. Paralelly, he left behind one of the most impressive geographical works, in a book that included many maps, including a map of the entire world. In the time of Ptolemy scholars already knew that the earth is a sphere and one of the innovations in Ptolemy’s maps was a global coordinate grid, which divides the sphere into parallel latitude lines and non-parallel longitude lines that connect at the poles. .  

In practice, the innovation was not made by Ptolemy, but most likely by Hipparchus, an astronomer who lived 300 years earlier, and is often described as (please act surprised) the greatest astronomer of the ancient times. However, Ptolemy implemented it well, and included maps with markings of these gridlines in his great manuscript Geography (or Geographia). The original manuscript was lost but parts of it were recreated thanks to its copies, as well as a world map as it was known at the time. One of Ptolemy’s mistakes was that he estimated that the world is a much smaller sphere than it actually is, but he did implement two important principles in his maps: the understanding that maps should be adjusted when transferred from a sphere to a flat sheet and the longitude and latitude grid lines.   

Navigating by deep familiarity with the features of the sea, such as waves, currents and wind. Stick maps made by natives of the Marshall Islands | Image:  LIBRARY OF CONGRESS, GEOGRAPHY AND MAP DIVISION / SCIENCE PHOTO LIBRARY

Crossing The Lines

Greek astronomer, Ptolemy (Claudius Ptolemy), who lived and practiced in Alexandria in the 2nd century B.C., is considered the greatest astronomer of the ancient time. More precisely, he is one of several astronomers that are commonly known as such. Much like other scholars of his time, Ptolemy did not limit himself to one specific discipline, probably for the better. His work in astronomy included detailed and thorough mapping of constellations, but also a false description of the solar system, based on the perception that the sun and other planets circumvent the earth, and also astrological studies. Paralelly, he left behind one of the most impressive geographical works, in a book that included many maps, including a map of the entire world. In the time of Ptolemy scholars already knew that the earth is a sphere and one of the innovations in Ptolemy’s maps was a global coordinate grid, which divides the sphere into parallel latitude lines and non-parallel longitude lines that connect at the poles. .  

In practice, the innovation was not made by Ptolemy, but most likely by Hipparchus, an astronomer who lived 300 years earlier, and is often described as (please act surprised) the greatest astronomer of the ancient times. However, Ptolemy implemented it well, and included maps with markings of these gridlines in his great manuscript Geography (or Geographia). The original manuscript was lost but parts of it were recreated thanks to its copies, as well as a world map as it was known at the time. One of Ptolemy’s mistakes was that he estimated that the world is a much smaller sphere than it actually is, but he did implement two important principles in his maps: the understanding that maps should be adjusted when transferred from a sphere to a flat sheet and the longitude and latitude grid lines.   

Global perception, including the implementation of a grid of latitude and longitude lines. Recreation of Ptolemy’s world map | Source: Morphart Creation, Shutterstock

Using such a grid, we can describe the location of every spot on the surface of the earth using two numbers: distance from the equator due north or south and distance from a longitude line that we will assign as zero, due east or west. As the level of accuracy of the numbers increases, so will the spot that they define become smaller and more specific. For example, in the intersection of the latitude line 37 degrees, 59 minutes and three seconds north (37°59′03″N) and the longitude line 23 degrees, 43 minutes and 41 seconds east (E23°43′41″) resides the city of Athens, capital of Greece. 

Alongside the concept of latitude lines, navigation aids were also created that enabled calculating a location using celestial objects. The simplest was an adjustable protractor, which could be aimed at a certain celestial object and measure its location. For example, if you measure the angle between the north star and the horizon and find that it is 30°, we can conclude that we are 30 degrees above the equator, or at the latitude line 30° north. Using maps you could now sail north or south until you reached your desired latitude line and then sail east or west until you reach your destination.  

The simple protractor quickly gave way to the Astrolabe (from Greek, star-taker), which is a combination of the same protractor with maps of the earth and latitude lines scale marks. It often also included sky maps, engraved on wooden or metal discs, and rotating relative to each other, so that the user can see and calculate their location in relation to multiple known constellations. The basic astrolabe was most likely invented in the 2nd century B.C. - some also attribute its invention to Hipparchus, and it improved navigation ability on land and at sea, if the conditions allowed for measurements. More sophisticated astrolabes also enabled calculating the time of day according to the location of celestial objects. The use of such instruments in a known location also helped in mapping the skies more accurately, for astronomers and navigators alike. 

A gridline that enables to define the location of any spot on earth using numbers. Longitude (right) and latitude lines | Anshuman Rath, Shutterstock

Finding North

Over 2,500 years ago, the existence of magnetic rocks that attract iron was already known in ancient Greece, China and probably other places. Such rocks had uses in rituals, games, predicting the future and more. The word magnet probably originated from the Greek city Magnesia, in present day Turkey, where many such rocks were found. It took over 1000 years more until the Chinese discovered that they could be used for navigation. A piece of iron thin enough to float on water, which was magnetized by rubbing it against such a rock, rotates on the surface of the water and points at the magnetic north. 

Such devices quickly became the compasses we know today, reaching Europe in the 12th century. Over the years they were introduced with small improvements, like scale marks that enabled highly accurate determination of the angle towards a certain object or the direction of movement, or a device that holds the needle and allows it to rotate with higher accuracy. But the basic principle remained unchanged. The compass points at earth’s magnetic north, and enables navigators on land or at sea to quickly and easily define directions. 

The compass is indeed not free of diversions and errors - the magnetic pole is not exactly located at the geographical pole, and when you draw near the poles compasses become less reliable. It can also be affected by local magnetic fields, like natural magnetic rocks or artificial ones like the iron halls of ships or electronic systems. But in most applications the magnetic compass is very handy and it completely revolutionized navigation You can use it in any weather and any time, and if you know where you are on the map, all that is left is to point the bow of the ship in the desired direction, according to the compass, and sail to your preferred destination.. 

Not free from inaccuracies, but the simple device revolutionized navigation. Planning a course using a compass and a map | Image: Paya Mona, Shutterstoc

Navigating With Your Eyes Closed

The birth of the compass also brought “dead reckoning” into the world, which is also called approximated navigation or computational navigation. If you have to sail to a place located 2,000 kilometers due southeast, you can point your ship in that direction, and if you know, supposedly, that you are traveling at a speed of 20 kilometers per hour, following 100 hours of sailing in that direction you will reach your destination. Such navigation could be dangerous, of course, especially if your equipment is unreliable, or if winds or currents set you off course. Additionally, it requires knowing the speed of travel. What sounds elementary nowadays was not so in the past. In the past, sailors could estimate their speed by the intensity of the wind or currents, or by the time of travel between known locations. Measuring time at sea was especially problematic, and was based on celestial objects, or other aids for measuring short time periods. 

One of the common methods to estimate speed at sea was to cast a heavy rod overboard, which is tied to a rolled rope with knots at set intervals. The sailor held the rope in his hands, measured a short time, for example half a minute, using a sand clock, and counted the number of knots that passed through his hands. As the ship travels faster, the rope is extended further and more knots pass through his hands in a given time period. This is the origin of the unit “knot” as a speed unit for marine travel. Naturally, it took years until the unit was standardized, long after ropes, knots and sand clocks became a thing of the past. Currently a knot is calculated as marine miles (1852 meters) per hour. In shipping, meteorology and aviation this unit is currently still in use, and when the skipper speaks about 20 knots winds, he is referring to wind speed of about 37 kilometers per hour.  

The ability to estimate traveling speed at sea greatly improves navigation possibilities, even if you do not rely on blind navigation. It enabled sailors to better estimate distances and cartographers to accordingly make their maps more accurate. It also illustrated the tight link between navigation and time measurement. 

Measuring direction and time allows for a certain estimation of location. A navigation kit of a British pilot in World War II, with a magnetic compass and watch in its center | Image: J.S.Bond, Wikipedia

Improving Accuracy

The more accurate maps were joined over the years with data tables. Those were the fruits of the labor of dedicated astronomers who documented and calculated the location of celestial objects in different locations in the world. For example, measuring the angle between the sun and the horizon at noon, can provide the latitude line with high accuracy, if we know the date (or provide the date if we know where we are), thanks to tables that detail such angles in every location and time. Other stars also help similarly. One of the astronomers that contributed such important tables in historical timing was Abraham Zakuto who worked in Spain and Portugal in the second half of the 15th century and the early 16th century. His work was published during one of the prominent eras of travel and discovery, helping sailors such as Cristopher Colombus, Vasco de Gama and others in their expeditions to discover America, circumvent Africa and additional places. 

Starting in the 18th century such tables were published regularly in almanacs, which became an important navigation aid. Almanac is a general name for a data book that is published yearly and navigation almanacs include tables that accurately detail the location of tens of stars and planets during every day and time of the year. Starting in 1767 the British Royal Observatory, in Greenwich, near London, began publishing its

yearly almanac. Other entities later began to publish their almanac, but the Greenwich almanac became a sort of reference point for global navigation.   

During the same time measurement of location of stars also improved significantly, thanks to a new device - the Sextant. Like the astrolabe, it was used to measure the angle between celestial objects, but much more accurately, by optical lenses. These innovations greatly improved marine navigation, but one major problem remained in humans’ orientation around our planet.   

Improved measurements of the angles between celestial objects and more accurate tables vastly improved the ability to determine one's location, at least relative to the latitude lines. A sextant placed on a map | Illustration: Triff, Shutterstock

The Longitude Lines

In October 1707 a fleet of 21 British ships made its way back to the kingdom from the war against Spain. A few days of harsh weather made it very difficult for the navigators to determine the location of the ships and on the 22nd of October many of them became stuck in sandbanks off Scilly island, east of the shores of Cornwall, the southwestern end of England. After a few days of sailing in harsh weather, with no possibility of determining their location, the navigators had to settle for estimations of the distance that the ships traveled. They figured that they were located roughly 300 kilometers southwest from their actual location, far from the dangerous sandbanks. This error caused one of the worst naval disasters in British history. Four ships sinked and others were badly damaged. At least 1400 sailors lost their lives. Though the disaster was caused by an aggregation of multiple errors and problems, the parliament in London chose to focus only on one of them, offering a reward to whoever solves the problem of determining the longitude value of a ship's location. 

As previously stated, it is relatively easy to calculate our location north or south relative to the equator by measuring angles of stars at night or of the sun during the day. But it is much harder to determine your location on the east-west axis The obvious solution is measuring time: if you know the exact time in the location you are at and the exact time in a certain reference point, with a known location, you can calculate the distance between you and the location due east or west using time differences. Using the sun, stars and tables in almanacs you can determine the time in the ship’s location, but knowing the exact time in the reference point is a tougher task. You could presumably bring a clock along with you - the problem was that mechanical clocks at the time were not accurate enough for prolonged time measurements under the sways and turmoil of marine travel. Pendulum clocks, which were sufficiently accurate, could not be used at sea, as they needed to be stable to operate properly.

The disaster that led to a solution. An engraving from the 18th century of the sinking of the ships in Scilly island, HMS Association located at the center of the illustration. Unknown artist | Source: Wikipedia, public domain. 

This challenge was faced by English carpenter and watchmaker John Harrison, who invested many years of his life into developing the marine chronometer - a clock that can operate properly under the swaying of a ship. His first versions were large and heavy, but the fourth chronometer, which he completed at the age of 68 following 13 more years of work, was small and easily carried. It proved its worth during the crossing of the Atlantic Ocean and practically solved the longitude line problem. All that you need is such a clock on board your ship, which will indicate the time at a known reference point. All that is left now is to determine local time at sea, compare it to the reference clock, and calculate your distance from it. Measuring the latitude is also very important, as in each latitude the circumference of the earth is different. Since Greenwich was already considered the astronomical reference point, its stature was also eternalized as a reference point for longitude calculations and the line that runs between the poles goes through Greenwich was designated longitude line zero. The term Greenwich Time was also common for many years as the reference time that we set other local clocks according to .

During the time when Harisson developed the marine chronometer, another method was developed to solve the longitude line problem - lunar distance measurements, which means measuring the height of the moon in the sky at a certain time and comparing it to the height in Greenwich using almanacs. Using such measurements, if the weather allows for them - you can calculate the longitude line with decent accuracy, but they required calculations that were far longer and more complicated than using the clock. Once clock prices went down to a reasonable level, using them to determine longitude lines quickly overtook other methods and once again demonstrated the tight link between navigation and time measurement. 

The practical solution to the longitude line problem enabled to easily determine the coordinates of a ship. The fifth model of John Harrison’s marine chronometer, which was small enough to be carried in one’s pocket | Image: Racklever, Wikipedia

Observing From Above

In 1886 German physicist Heinrich Hertz was successful in transferring a flash between two electric wires that were not touching each other. Next, he increased the distance between the wire to a few meters and demonstrated that the invisible radiation that transfers between them moves at the speed of light. Those were the first experiments in transmitting electromagnetic radiation. Scientists who followed Hertz understood the great potential of the discovery, and in about two decades radio waves were already transmitted between America and Europe, a distance of thousands of kilometers.

The young technology had vast potential not only in communication, but also for navigation. For example, a marine vessel can orient itself according to a radio signal it receives from a distance, and easily find its path, even in stormy weather with no possibility of performing location measurements. With relatively simple mathematics, using the triangulation method, you can calculate the distance of a radio transmitter or receiver, if it communicates with two antennas at known locations, and the angle between it and the antennas. A more sophisticated method, trilateration, enables to accurately determine the location of an object according to its distance from three locations, when use of more locations can increase accuracy (multilateration)  

Radio did not only change marine navigation, but also had a significant effect on the developing field of aerial navigation in the early 20th century. While humans already took to the skies in the 18th century, they did it using balloons that there was no real possibility to stir them. The age of motorized aviation brought the need to develop devices for navigating airships and later airplanes. In a relatively short time both airplanes and electronics were greatly improved so that every airplane could be equipped with a radio transmitter and receiver. Ratio signals help airplanes and other vehicles to find their way, but they are not always enough. For radio navigation there is a requirement for ground stations that broadcast the proper signals and those do not exist everywhere. Over enemy territory suitable antennas could disrupt the radio reception of the airplanes, or purposely transmit signals to confuse them. There is also always the possibility of equipment malfunctioning, so that despite its importance, pilots cannot rely on radio alone. 

Even today radio signals are used for navigating airplanes and other vehicles. An array of antennas and lights at Dusseldorf airport, Germany |  Image: Rene Hausotte, Shutterstock

Inventing The Wheel

The name of French physicist, Leon Foucault, is mostly known today thanks to the pendulum named after him, which illustrates earth’s rotation. Foucault performed his famous demonstration in 1851, but continued searching for methods to measure earth’s movement and alterations in it. This is how he developed the gyroscope - a device that is composed of a disk spinning on its axis, with almost no friction. As long as the disk is spinning, momentum preservation causes the device to resist any changes in the spin axis direction, exerting momentum perpendicularly to the direction of the change . 

In the days of Foucault there were no means to continue the spin indefinitely, but those who followed his path understood the immense potential of the gyroscope, for example in stabilizing ships and later airplanes, and also in its use as a compass. If we direct the spin axis so that the device points north, it will continue to do so as long as the disk is spinning, and if we diverge from our course, we can use the gyroscope to measure the diversion. Unlike the magnetic compass, the gyroscope is not affected by local magnetic fields, other devices or proximity to the pole, and does not have to remain balanced to operate. If a plane takes a sharp turn, for example, leaning on its side, the magnetic compass is useless, while a gyroscope can not only continue to operate, but can also display the plane’s turn angle to the pilot.

The wheel that changed the face of navigation, which can be used as a compass as well as for balancing aircrafts | Image: Tatiana Shepeleva, Shutterstock

Developing efficient gyroscopes for aviation was a great challenge, but it paid off. As the gyroscope can both point in the right direction and also maintain it by balancing the airplane, it served as the basis for developing automatic pilot systems. The American pilot, Leonard Sperry, developed such a system using knowledge he received from his father, Elmer, one of the inventors of the gyroscopic compass. In June 1914, during a contest in the field of safety innovation in aviation held in France, young Sperry demonstrated his balancing system with a hair raising stunt. In his first passage in front of the judges’ booth he waved both hands at them, demonstrating that he was not piloting the plane - it was maintaining its course by itself. In the second passage, his flight mechanic Emil Cachin, left his seat and crawled to the edge of the wing while Sperry kept waving his hands, showing that the airplane was stabilizing itself, despite the extreme shift in weight distribution. 

Over time gyroscopes became an inseparable component of any flight system, and even devices such as artificial horizon, which displays the roll (side turn) and pitch (direction of the plane’s nose in relation to the horizon) of the plane, are based on them. 

Another important addition to gyroscopes was the accelerometer, which enables one to measure the changes in speed of the device at any given moment. Thanks to stabilizing gyroscopes such a system can measure acceleration in any of the three movement axes of an aircraft, and provide information regarding changes in its location. 

A system based on gyroscopes and accelerometers can be used for accurate computational navigation. If we provide the system with the precise coordinates of our starting location and our initial velocity, we can accurately and continually calculate changes in speed and direction, and thus our precise location, with no need for a radio device or any external source of data. These days such navigation is called Inertial Navigation. It is not only important in airplanes or marine vessels, but is also used in submarines, which can stay submerged for many weeks with no communication with the outside world. Such navigation is also used in unmanned aircrafts, and even in weapons such as cruise and ballistic missiles that have to go through great lengths and hit a distant target with high accuracy, without relying on external data like radio signals, which could be disrupted by defensive systems.   

Over the years mechanical gyroscopes were replaced with gyroscopic systems that are based on measurements of the degree of change in the rotation of laser beams. Such systems exhibit very high accuracy and are primarily very small. Such gyroscopes combined with accelerometers are currently installed in any smartphone. This enables the phone to rotate the image on the screen according to the position of the device, or stabilize the camera to receive a sharp image, even if we took the image with a shaky hand. They also enable accurate measurement of the movement, angle and speed of the phone, supporting the development of different applications. For example, there are apps that automatically alert if the device’s speed decreased abruptly, in case the owner of the device was in a car accident and cannot notify about it on their own.  

Combining electronic and mechanical gyroscopes with accelerometers enables one to calculate the location of an aircraft at any location, even on its way to the moon. The inertial navigation system of the Apollo spaceship | Image: ArnoldReinhold, Wikipedia

Observing From Higher Above

On October 4th, 1957, the Soviet Union launched its first satellite. Sputnik became the first artificial object to enter orbit around earth, and the only device on it was a radio transmitter, which broadcasted a steady signal. Scientists and radio enthusiasts around the world followed the satellite in space using these signals, but some American scientists understood already then that it can also work the other way: if we know the exact course of the satellite, the timing and manner of receiving the signal can let us know where we are. 

In a few years the United States started the Transit system, which was mainly intended to provide accurate location for submarines that were armed with ballistic missiles that carry nuclear warheads. Inertial navigation systems, mainly those of these times, tended to accumulate inaccuracies over time. To improve the chances that a missile launched from a submarine will hit its target, you have to update it with a starting location that is as accurate as possible. The system included four satellites and was meant to provide submarines with a satellite signal in a relatively short time, so that it could launch its missile and disappear again under the surface of the water. 

The transit system was later replaced with other systems, with more satellites. Over the years the U.S. developed its military positioning system for general use, GPS - which stands for Global Positioning System - and currently anyone can use it, as well as several alternative systems by other countries. 

The basis of this positioning system is that at any second every location on earth is in a direct line with multiple satellites. Each satellite transmits an accurate time signal towards earth. A receiver that received this signal can compare the reception time to the sending time and so calculate the distance that the signal passed through. By cross referensing multiple such signals from satellites at known locations, you can accurately calculate the receiver’s location. The time signal must be very accurate and highly synchronized between satellites and consumers, and so satellites are equipped with atomic clocks, which measure time with very high accuracy. Again - a reminder of the tight link between navigation and time measurement, even in the 21st century.  

With the advancement of technology, the receivers were miniaturized to a degree that almost all of us carry in our smartphones a microchip that enables us to determine its location with an accuracy of a few meters, and even less. By crossing such data with map applications in our phone, we can not only know the geographical coordinates of our location, but also in which street we are on, next to which house and how to get from there to our desired location - on foot, in a private car, or by public transportation, anywhere on earth. 

These days almost everyone carries in their smartphone a chip that receives the time signals from navigation satellites and can determine its location with an accuracy of meters | Illustration: Bakhtiar Zein, Shutterstock

Seeing Stars

Thanks to technology and satellites we can easily find our location at any point on earth, even if we are flying above it in a plane or even a spaceship. But what do you do when you travel far from it? How do you navigate in deep space?

Navigation devices in space are very similar in principle to those used on earth. In every spaceship there are gyroscopes with accelerometers that measure the ship’s location and state in the three motion axes. In spaceships the direction is especially important when you wish to use your engine to change course, as the thrust must be pointed in the right direction. Knowing the precise direction is also important for pointing antennas towards earth, to align solar panels to the sun and more.

Even in space they navigate with a sextant and measure the angles between stars. Astronaut Jom Lovell measuring distance to stars in the navigation system of the Apollo 8 spaceship | Image: NASA

In space you can also use computational navigation and it is even easier to do so. The speed hardly ever changes unless you use your engine, and if you point the spaceship in the right direction and accelerate it to the proper speed, there is a good chance that it will arrive at its destination. To make certain that this happens, the spaceship can make course correction, by examining its location in space. How do you do this without GPS satellites? by using the stars. You choose a few prominent stars in the sky, measure the exact angle to them, and calculate your location relative to them. While in the Apollo spaceships astronauts did this manually, using a telescope, today this is no longer necessary. Many spaceships are equipped with “star trackers” - sophisticated computerized cameras that scan the skies, measure the angle to these stars and calculate the location of the spaceship relative to its destined course.  

Thus, thousands of years after ancient nomads and sailors gazed at the night skies to determine their location, humanity still uses the same stars to navigate, if via more advanced technology and to destinations that our forefathers could only dream of.