History of Navigation |
Methods of Navigation There exist many methods of navigation, some more sophisticated than the rest, but all serve the same purpose : to answer the question of how to get from one point to another. In this project, we shall discuss 2 methods : celestial navigation and navigation via the GPS (Global Positioning System). Celestial Navigation What is celestial navigation? In its simplest form, it is simply navigation using the relative positions of the celestial bodies : sun, moon and stars. Man has been looking up at the sky above to find our way from the start of our history. People living in the desert as well as sea-farers have all depended on the stars to find their way . Which is not surprising. Out in the bare expanse of the desert and oceans, there are very few prominent landmarks which can be used for finding your way around. The most prominent objects around would be the celestial bodies. For this reason many stars have Arabic names , eg Aschere, Suhail, Toliman, Haris-el-sema, Fidis are the 5 brightest stars in the sky (after the Sun) in descending order. How celestial navigation works is that a geocentric point of view of the universe is taken. This means that everything is assumed to revolve around the earth. Why? Celestial navigation was developed way before Nicolaus Copernicus (1473-1543) proved to the world that everything revolves around the Sun ie he developed a heliocentric model of the solar system in his theory On the revolutions of the Heavenly Spheres . This does not mean that all previous observations and recordings of how the celestial bodies move in relation to one another is wrong. The theory as to what is the center of the universe (the Earth) is wrong, but the empirical data as to how the celestial bodies move with respect to the Earth still holds true. Its all about the relative motion of the heavenly bodies with respect to the earth. All this data that has been collected over the years on the relative motion of the heavenly bodies has been compiled in almanacs and the compiled data is used as a reference when determining one's position using the sextant. In the past, almanacs came in the form of books, which had to be updated manually after a certain period of time. Nowadays, with the advent of the Internet, almanacs are available online and in the form of software. The online versions are constantly updated and thus provide the most up-to-date information, while the software versions are easily updated. Some examples are the Stormfax Celestial Almanac , Stormy Weather Software Alliance's Nautical and Astronomical Almanac and The Online Nautical Almanac . How exactly the data from the almanacs together with readings taken from the sextant are used to plot one's location is shown in a later section. Development of Latitude and Longitude Co-ordinates on a map are known as latitude and longitude. Latitudes are imaginary circles on the earth parallel to the Equator, and are measured in degrees. Latitudes of interest include the Equator (o°), Tropic of Cancer (23.5 °N), Tropic of Capricorn (23.5°S), the North Pole (90°N) and the South Pole (90°S). Longitudes are imaginary lines joining the North Pole, South Pole and the Sun's position at zenith over the Equator. They are measured in degrees from the Greenwich Meridian (0°). Longitudes to the right of the Greenwich Meridian are marked as x° E, while longitudes to the left are marked as x° W. A difference of an hour between different time zones represents a difference of 15° in longitude. |
The History of the Sextant Before the introduction of satellite-supported systems (GPS) the most important method of navigating on the high seas was the measurement of distances between constellations and the altitude of such above the horizon to the highest possible degree of exactitude. The Polynesians used something similar to a sextant without mirrors a latitude hook. This was a long needle shaped instrument, used to measure the distance between the Sun, Moon or a star (through the 'eye') and the horizon. Over the centuries, similar navigational instruments were developed to measure the angles between a celestial body and the horizon. Around the 9th century the equipment used for these calculations comprised the quadrant and the astrolabe, and that was still long before the broad use of the magnetic compass. With the invention in the 14th century of the cross staff it was then possible to achieve even more exact readings and this piece of equipment was to remain the seaman's most important navigational instrument for the next 400 years. Around the early 1700s, the famous scientists Isaac Newton, Edmund Halley, Robert Hooke and John Hadley all had similar theories which lead to the development of the sextant. In 1731 in London, John Hadley introduced his mirror sextant. At the same time, in Philadelphia, and independently of him, Thomas Godfrey had produced the same invention. This instrument revolutionized navigation because it was now possible to take readings of, for example, the height of the sun with unsurpassed accuracy and speed. In connection with John Harrison's invention, the chronometer, the art of navigation reached heights of development never known before and one can say confidently, without exaggeration, that these 2 inventions were the most important prerequisites for the spreading, world wide of the British Empire. The principle is ingenious and at the same time amazingly simple: A rotating mirror makes it possible to bring the images of the point to be measured and of the horizon or another point of reference to coincide, and the angle of the distance between the two is simply read on a scale (more exactly: the angle produced by the lines of vision to the 2 points). It is hardly surprising that the sextant was often the most precious possession of a seaman and that it is, even today, along with the anchor and the compass the most famous nautical symbol. |
History of GPS People have always wondered 'where am I?'. The people that tend to ask this question the most are sailors and soldiers. Why? Knowing their exact position is sometimes a life and death question. In the beginning, there was celestial navigation. Knowledge of the movements of the celestial bodies together with the help of an almanac, provided a system to which they could plot their position to within a mile of where they were. Not very accurate, but better than not knowing where they were at all. In the 1920s, with the advent in radar technology, navigators were able to determine their position using radio sets. These radio sets were able to determine their distance from transmission stations whose location was known. Thus by simple calculation, one's position could be calculated fairly accurately. The disadvantage of this technology was that you had to be in range of the transmission station's radar to be able to receive its transmissions. Also, radar travels in a straight line, thus it its of no use unless you have line-of-sight with it. (not that you must be able to see it, just that there must be a clear path between the radio set and the transmission station) Thus, method of radio-navigation becomes relatively useless when trying to determine one's location in a mountainous region. Accordingly, radio-navigation was most commonly used by sailors, as seas are generally 'flat' ie everything is at sea-level. The GPS was developed by the United States Military as an all-weather, accurate positioning and navigation system for use 24 hours a day, 7 days a week. It is interesting to note that war, or the threat of war, has driven Man to the development of new technologies. Nuclear technology in the 1940s-50s (for 'better' nuclear weapons), biological research in the 1960s-70s (for 'better' chemical/biological warfare agents) and now the GPS, developed in the 1970s (for more accurate delivery of missiles). In what we create for destruction, we can find better use for the improvement of our lives. The GPS is basically a constellation of 24 satellites (GPS satellites) at high altitude in geosynchronous orbit (each sending out a different signal), and with a receiver, one can accurately pinpoint his location within a few seconds. Since the 16th of September 1983, following the crash of Korean Airlines KAL 007 due to lack of navigational data, usage of the GPS on commercial airlines free of charge had been allowed, by executive order by the then President of the United States Ronald.(KAL 007 had strayed into Soviet airspace and was shot down by a jet. It's believed that the crew thought they were sill in the safety of international airspace because of their lack of navigation data) Even so, the GPS signals that were allowed for civilian and commercial use by the US government by degraded ie the signals sent out were 'rounded-off', giving readings on civilian use that were nowhere as accurate as the readings available to the US military. This was known as SA, or Selective Availability. The rationale behind this scheme was to prevent any enemy regime from using the GPS as a free, highly accurate navigational system for the delivery of missiles against US targets. It was only on the 1st of May 2000 that the then President of the United States Bill Clinton, passed an executive order to remove SA from GPS signals. This meant that for the first time, civilian and commercial users of the system could be sure that they were where the GPS receiver said they were. This was done in the interest of public benefit eg emergency services responding to an accident call would know which side of the highway the accident had occurred on. However, the US held on to a safeguard : they had the capability to withhold GPS transmission over selected regions when they felt that the US's national security was compromised. THE WHITE HOUSE Office of the Press Secretary For Immediate Release May 1, 2000 Today, I am pleased to announce that the United States will stop the intentional degradation of the Global Positioning System (GPS) signals available to the public beginning at midnight tonight. We call this degradation feature Selective Availability (SA). This will mean that civilian users of GPS will be able to pinpoint locations up to ten times more accurately than they do now. GPS is a dual-use, satellite-based system that provides accurate location and timing data to users worldwide. My March 1996 Presidential Decision Directive included in the goals for GPS to: "encourage acceptance and integration of GPS into peaceful civil, commercial and scientific applications worldwide; and to encourage private sector investment in and use of U.S. GPS technologies and services." To meet these goals, I committed the U.S. to discontinuing the use of SA by 2006 with an annual assessment of its continued use beginning this year. The decision to discontinue SA is the latest measure in an on-going effort to make GPS more responsive to civil and commercial users worldwide. Last year, Vice President Gore announced our plans to modernize GPS by adding two new civilian signals to enhance the civil and commercial service. This initiative is on-track and the budget further advances modernization by incorporating some of the new features on up to 18 additional satellites that are already awaiting launch or are in production. We will continue to provide all of these capabilities to worldwide users free of charge. My decision to discontinue SA was based upon a recommendation by the Secretary of Defense in coordination with the Departments of State, Transportation, Commerce, the Director of Central Intelligence, and other Executive Branch Departments and Agencies. They realized that worldwide transportation safety, scientific, and commercial interests could best be served by discontinuation of SA. Along with our commitment to enhance GPS for peaceful applications, my administration is committed to preserving fully the military utility of GPS. The decision to discontinue SA is coupled with our continuing efforts to upgrade the military utility of our systems that use GPS, and is supported by threat assessments which conclude that setting SA to zero at this time would have minimal impact on national security. Additionally, we have demonstrated the capability to selectively deny GPS signals on a regional basis when our national security is threatened. This regional approach to denying navigation services is consistent with the 1996 plan to discontinue the degradation of civil and commercial GPS service globally through the SA technique. Originally developed by the Department of Defense as a military system, GPS has become a global utility. It benefits users around the world in many different applications, including air, road, marine, and rail navigation, telecommunications, emergency response, oil exploration, mining, and many more. Civilian users will realize a dramatic improvement in GPS accuracy with the discontinuation of SA. For example, emergency teams responding to a cry for help can now determine what side of the highway they must respond to, thereby saving precious minutes. This increase in accuracy will allow new GPS applications to emerge and continue to enhance the lives of people around the world. |
Latitudes are more easily calculated than longitude. For one thing, latitude is more easily defined, as its base circle is a natural and obvious choice (the Equator lying directly between the North and South Poles) whilst longitude is measured from a man-made reference point (the Greenwich Meridian). To determine latitude, all one needed was a calendar to know what time of the year it was, and a sextant. By simply determining the Sun's altitude in the day, one could determine their own latitude to a fair degree of accuracy. |
Longitudes were another matter. Knowing one's longitude required two readings : Local time and the time at some reference point eg the Greenwich Meridian. Determining local time was not a problem, as it only required observation of the Sun. Knowing the time at the reference point required the use of an accurate time-keeping mechanism. On land, this wasn't much of a problem, as clocks could be constructed and used at relatively constant environmental conditions. The problems and difficulty of determining latitude and longitude were faced most often by sailors. Thus, the time-keeping mechanism for these ocean farers not only needed to be accurate, it also needed to compensate for the fluctuations in humidity and temperature whilst out at sea. This posed a challenge great enough that King Charles II found the Royal Observatory in 1675 to solve the problem of finding longitude at sea. The mission of the Observatory was to accurately catalog the positions of the stars in the sky, and the position of the Moon relative to the stars at different times. Thus, by careful observation observations of the Moon and the stars, the time at Greenwich could be calculated. By comparing this with local time, the longitude could be calculated. This method is known as the Lunar Distance Method. However, an easier and more accurate method needed to be developed for obvious reasons : what if one can't see the Moon or the stars on certain nights eg on the night of a new moon? Or if local time cannot be easily determined, especially at night when the Sun cannot be observed? It was because of this that in 1714 the British government offered 20 000 pounds to anyone who could provide a solution to finding longitude to within half a degree, or having an error of at most 2 minutes in determining Greenwich time. The prize was won by John Harrison (1693-1776) in 1773. With little formal education, but with great insight, he constructed, of all things, a pocket watch, which he called H4, that kept time to an error of 39.2 seconds over a voyage of 47 days, three times better than the standard set by the British government! H4 was able to take into account the fluctuations in humidity and temperature at sea, and proved that longitude could be determined by the simple use of a watch. |
Now to Miletos he steered his course That was the teaching of old Thales Who in bygone days gauged the stars Of the Little Bear by which the Phoenicians Steered across the seas Thales of Miletos ( 624-547 B.C ) |
John Hadley's mirror sextant |
GPS device |
Why the need for navigation? Man has always had the desire or need to move from one place to another, and then get back, since time immemorial. This could either be for reasons of survival (better foraging/hunting grounds, escape from enemies), to find a better living (westward expansion in the United States in the 19th century) or for exploration (Lewis and Clark's exploration of the American landscape in the early 19th century, Magellan's journeys). Explorers faced the same basic problems : How to get where I want to go, and how do I get back? Undoubtedly, the art/science of navigation has its roots in these explorers. For example primitive man could have found an area for good hunting, where migrating herds come to rest every year. To remember how to get from his home (or cave) to his 'happy hunting grounds' thus becomes very important to him as it is a matter of survival. By remembering landmarks along the route to his hunting grounds, primitive man evolved a basic rule of navigation : the use of waypoints (the landmarks). A system, though primitive, for knowing how to get from one point to another and back was developed. The next question : how to pass down this information to his son and/or fellow tribesmen? Orally? Possible, but verbal instructions usually get jumbled up after being passed a few times (remember the Chinese Whispers game?) A more concrete form of recording how to get from home to hunting ground had to be discovered. Cave drawings! Probably the GPS of their time, it allowed primitive man to just point to the wall behind him instead of relating the entire story of how he killed 3 buffalo and brought home enough meat to last through the winter. Apart from looking good, it also made sure everyone and anyone who wanted to know how to get to a certain place would be able to get there (if the person knew how to read the writings on the walls) without the confusion caused by the passing of information orally. A primitive form of recording had been developed. As Man has progressed in terms of science, technology and understanding of how the world around us operates, we have come up with new instruments, methods and technologies to help us on our way. Exploring and finding new lands wasn't enough, we had to know how to get back to where we were. Many skills were developed, including cartography (plotting of maps), celestial navigation (navigation using the relative positions of the celestial bodies), to aid us in our quest. Many tools were also created along the way : the sextant, the astrolabe, compasses etc. |
Notable figures Navigation is not something you practise in a room in comfort and safety. Techniques may be learnt this way, but you would never really explored if you did not take the risk and actually explore the world around you. Here are men that were explorers. Ferdinand Magellan (1480-1521) Ferdinand Magellan was an explorer born in Portugal who renounced his citizenship, swearing allegiance to the king of Spain instead. This was because he felt his talents and skills were underused and undervalued. The mission of his voyage of discovery which began in 1519 was to discover new lands (the Spice Islands) where spice and other goods could be traded, and his explorations took him from Seville, Spain, to Cape St. Augustine, Brazil, and finally to the Philippines, where he was killed by the natives in 1521. What is of note is that Magellan was the first man to complete the circumnavigation of the real world. This had profound effects in the areas of science (it proved that the world was round) and geography. (it gave the first true idea of how land mass and the sea was distributed.) Meriwether Lewis (1774-1809) and William Clark (1770-1838) Lewis and Clark were born in the state of Virginia, in the United States of America. It was a time when the United States was just 18 years old. Lewis and Clark were sent on their Corps of Discovery to explore and chart the unexplored West. The significance of the Corps of Discovery was that it dispelled common myths of the unexplored West that the Americans at that time: the presence of woolly mammoths, Peruvian llamas and blue-eyed Welsh speaking Indians. It also paved the way for the westward expansion of the nation in the 17th century, and in a way, it also helped the United States become the nation of 50 states that we know today. |