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The Longitude Question On October 22nd, 1707 a British Naval Fleet sank of within minutes after running onto the rocks of the Scilly Isles. 1647 sailors died. (Oh, and several treasure chests of great value also went to the bottom of the English Channel.) It was one of the greatest maritime disasters in the history of the British Isles. People freaked. It was later determined that the main cause of the disaster was the navigators' inability to accurately calculate their longitude, or east/west location. Lands within British Empire at any time For the British and other imperialist powers like Spain and France, accurate navigation at sea was a key to controlling their growing empires. The magnitude of the problem was illustrated by the 1497 voyage of the Portuguese navigator Cabral who, on his way to the East Indies, ran into the coast of Brazil, some 2,000 miles off course! In response to the Scilly Islands tragedy, the British Parliament passed the Longitude Act promising a reward of £ 20,000 to anyone who could solve the so called “Longitude Problem”, one of the most vexing scientific problems of the time. Note that £20,000 in 1714 is around $4.7 million dollars today! What is my latitude (north/south position)? Easy! What is my longitude (east/west position)? Hard! But why was measuring longitude, one’s position east to west, a problem at all? After all, sailors had been measuring latitude (one’s north south position) with ease since ancient times. Why the difference? To answer that question, we need to understand what latitude and longitude are, what each measures, and how one is scientifically derived from the earth’s rotation around the sun and the other is a function of time and is therefore purely a human creation. The location of any place on the earth’s surface can be described by parallels (lines parallel to the equator) and meridians (lines running from pole to pole), two sets of imaginary arcs drawn on the earth’s surface. Note that parallels are circles while meridians are half circles. The numbering system to indicate the location of any parallel is called latitude. The numbering system to indicate the location of meridians is called longitude. Parallels are about 69 miles apart per degree. (Arroyo Grande is at 35⁰ N and King City (about 70 miles north of AG) is at 36⁰ N latitude. However, since meridians converge at the poles, the distance between them is not constant. It becomes smaller the closer you get to the poles. Lines of latitude run east to west but they tell you your north/south position (how far you are north or south of the equator). The equator is 0⁰ latitude. All other parallels have latitude numbers between 0⁰ and 90⁰ either north or south depending on whether they are north or south of the equator. Latitude lines above the equator are labeled N (North) 30⁰ N Latitude lines below the equator are labeled S (South) 45⁰ S Lines of longitude run north to south but they tell you your east/west position (how far you are east or west of the prime meridian. The prime meridian, which runs through Greenwich, England, is 0⁰ longitude. All other meridians have longitude numbers between 0⁰ and 180⁰ east or west depending on whether they are east or west of prime meridian. All locations east of the Prime Meridian have longitudes from 0⁰ to 180⁰ E The Prime Meridian at Greenwich, England is the meridian a 0⁰ latitude. All locations west of the Prime Meridian have longitudes from 0⁰ to 180⁰ W. Arroyo Grande is at about 120⁰ W latitude. The prime meridian divides the earth into western and eastern hemispheres. The equator divides the earth into northern and southern hemispheres. Five Key Parallels and their Latitudes: North Pole 90°N 66°N Arroyo Grande 35°N 23.5°N 0° 23.5°S 66°S South Pole The Tropics of Cancer and Capricorn are the latitudes at which the sun is directly overhead at the summer solstices (June 21 in the northern hemisphere and December 21 in the southern hemisphere.) North and south of these lines the sun is never directly overhead. The zone in between the Tropic of Cancer and the Tropic of Capricorn is known as – wait for it – the tropics. The Arctic and Antarctic Circles are the latitudes above which the sun is above the horizon for 24 continuous hours at least once per year and below the horizon for 24 continuous hours at least once per year. The areas between the tropics and the arctic circles (marked in pink above) are known as the Northern and Southern Temperate Zones. Along with the five major parallels, you should know the two main meridians: the prime meridian at 0⁰ longitude which runs through Greenwich, England and, opposite from it at 180⁰ E or W longitude (same place), the international date line. Since the meridian at 180⁰ longitude runs through several countries, it would divide those countries not simply into two different time zones, but into two different calendar days. To avoid such unnecessary confusion, the date line dips and bends around countries to permit them to share the same time. At the 1884 international meridian conference in Washington, DC, 24 standardized time zones were agreed to, each spanning 15⁰ of longitude. (24 x 15⁰=360⁰) Measuring one’s latitude was fairly easy because latitude is related to the angle of the sun or a star above the horizon, which is something humans figured out how to do very early on (around 4000 BCE). From ancient times sailors determined their latitude by using instruments such as the astrolab (left) and later the sextant (right) to determine the angle of the sun (or a star) above the horizon. The farther one is from the equator, the lower the midday sun (or star) appears in the sky. Once you knew the angle of the sun or star, it was a simple matter of consulting a table which would give you your latitude based on the known angle of the sun or star above the horizon for that day. Measuring one’s longitude (east-west position) was not so easy because longitude is related to time which was difficult to measure accurately, especially at sea. For centuries it was known that all one needed to determine one’s longitude was a clock on board that told you what time it was back at the prime meridian at Greenwich, England (or at any other place with a known longitude). When the sun reached its highest point above your ship, you knew it was 12 p.m. your time. Each hour of difference between your time (12 p.m.) and the time back at Greenwich was equal to 15⁰ of longitude. So if your Greenwich clock said 2 p.m. you knew you were at 30⁰ W longitude. The problem was that most clocks were extremely inaccurate—gaining or losing a minute or more each day—and even then, they were based on delicate mechanisms (such as pendulums) that would be thrown completely out of kilter on a rocking ship. A few days out of port, you could of course still know when it was 12 p.m. for you (the sun would be at its highest point) but your reference clock (telling you the time back at Greenwich) would be worthless. In 1613 Galileo proposed a brilliant solution to the so called “longitude problem”. He realized that the positions of Jupiter’s moons could function as a clock that would be observable from any place on earth. This failed however because the telescopes in use could not measure the position of these moons accurately, especially at sea. The solution to the longitude problem was eventually solved not by any of the great scientists of the day but rather by an uneducated British carpenter and mechanic by the name of John Harrison who was really really good at making clocks. At age 20, for example, he made a clock completely out of wood that lubricated itself by using the resins that naturally seeped from the wood. At age 42, after seven years of painstaking work in pursuit of the Longitude Act Prize, he completed his H1, his first “sea” clock meant to function at sea. However it was not accurate enough to win the prize. So he went back to work. At the age of 68, Harrison completed his masterpiece, the H4. In a test voyage to Jamaica, sailors using the H4 calculated their longitude to within two miles, well within the accuracy required for payment of the £20,000 Longitude Prize. Foul Play! Getting the prize money from the board was a different matter, however. They had intended that the prize go to a proper gentleman, not a simple working class carpenter like John Harrison. So they proclaimed the results of the test voyage to have been pure luck and refused to give Harrison the prize. Finally in 1773, when Harrison was on this death bed, King George III intervened on his behalf and granted him £ 20,000 for his achievements in solving the centuries old longitude problem. But he never received the official award (which was never awarded to anyone). Harrison’s design for marine chronometers was so good that even though other craftsmen found other ways to manufacture them, his template remained in use until microchips heralded the use of electronic chronometers in the 1980’s. Dava Sobel has written a great book about the longitude problem simply called Longitude. “Dava Sobel has written a gem of a book. Longitude is one of the best reads for the non-scientific mind to come along in many a moon”. Financial Times