The activity Where Am I? helps students use triangulation to find a lost classmate.
How do we get a perspective on our surroundings? We take a look around. If you lie on the ground, stand on a hill, or climb a tower, your perspective changes. If you go up in an airplane or a space capsule, your view changes even more. For thousands of years, humans have looked up to the heavens. Now we can go to the heavens to look back at ourselves.
What is the history that has led up to the new way in which we look at our home planet? The first maps were probably sketches in the dirt. A small clay tablet 4000 years old is the oldest known map, depicting a river valley in Mesopotamia (now Iraq). Polynesians made charts of their region using woven palm fibers to show the wave patterns of the Pacific Ocean. Sea shells marked the location of islands. Eskimos carved their coastal features on pieces of driftwood. Even from earliest times, people realized that a picture was worth a thousand words.
Who knew the Earth was round and when did they know it?
People knew the Earth was round 2500 years ago. They just forgot.
Because Earth-bound observers could only view a small section of the globe at a time, it wasn't possible to tell from direct observation whether the Earth was a flat disk or a sphere. The Greeks were the first to theorize that the Earth was round. Scholars like Pythagoras in 500 BC based their belief on observations about the way the altitudes of stars varied at different places on Earth and how ships appeared on the horizon. As a ship returned to port, first its mast tops, then the sails, and finally its hull gradually came into view. Aristotle, who lived 300 years before Christ, observed that the Earth cast a round shadow on the moon. When a light is shined on a sphere, it casts the same shadow. The Greeks calculated the general size and shape of the Earth. They also created the grid system of latitude and longitude, so that with just two coordinates one can locate any point on the Earth. Greek philosophers also concluded that the Earth could only be a sphere because that, in their opinion, was the "most perfect" shape.
Around 150 AD, Claudius Ptolemy, a Greek geographer, mathematician, and astronomer, compiled an encyclopedia of the ancient world from the archives of a legendary library in Alexandria, Egypt. His eight-volume Geography included extensive maps of the known world, all based on a curved globe.
Unfortunately, learning and intellect went out of fashion in Europe between 400 and 1200 AD. The storehouses of Greek knowledge were lost to Western society with the advent of the gloomy period known as the Dark Ages. Sea monsters and Vikings ruled the seas, and ships that ventured too far from shore were sure to fall off the edge of a flat Earth. Maps made in that time were based on religious beliefs or superstitions, not on observations, calculations, or scientific inquiry. Rectangular maps of the Earth represented the "four corners of the Earth." Circular maps usually placed the birthplace of Christianity, the holy city of Jerusalem, at the center of the world.
After 1250, map making in Europe took a turn for the better. Land maps and nautical charts were produced for travelers using measurements and observation rather than mythology and literary sources.
In Europe, the Middle Ages progressed into the Age of Discovery. Meanwhile, the Arab world had preserved Ptolemy's Geography. Ptolemy's works were rediscovered by the Western world and translated into Latin. Ptolemy's map projections explaining how to represent a sphere on a flat piece of paper enabled cartographers and explorers to chart newly-discovered lands and seas. The invention of the printing press made it possible for more people to use, circulate, and refine maps.
Christopher Columbus' voyage in 1492 confirmed that the Earth was round. Magellan's crew proved the fact definitively by circling the globe on a three-year voyage from 1519-1522. Map making joined hand in hand with the Age of Discovery.
Ferdinand Magellan (c.1480-1521) was a Portuguese sea captain who launched an expedition funded by Spain to find a new route to the Spice Islands, north of Australia. Magellan is credited with leading the first expedition to circumnavigate the globe, but he didn't live to complete his journey. After weathering storms, several mutinies, animosity between Portuguese and Spanish crew members, and near starvation when they were forced to eat rats, ox hides, and sawdust, they landed in the Philippine Islands. Although they were welcomed there by the natives, Magellan became involved in local politics and was killed in a battle between two rival factions of Filipinos on Mactan Island.
Magellan discovered the passage between the Atlantic and the Pacific Oceans at the tip of South America, which became known as the Straits of Magellan. As he passed through the straits, he and his crew became the first Europeans to sail into the "new" ocean. Magellan named it Pacific (which means peaceful) because it appeared calm after the stormy Atlantic. In reality, the Straits of Magellan and the Pacific Ocean are noted for their high winds, giant waves, and violent weather.
It took Magellan's crew three years to complete their voyage, while today it takes a satellite about 100 minutes to circumnavigate the globe.
This boom in map making, or cartography, served many purposes. Knowledge of coastlines, hills, roads, houses, and town and country boundaries enabled colonists, generals, and tax collectors to claim land, prepare for invasions, mark strategic defensive positions, quell local rebellions, and levy taxes.
Knowledge is power
In the latter half of the 17th century, distances on English maps were first recorded in statute miles of 5280 feet. Surveyors measured actual distances by counting the number of revolutions of a foot-wheel. In this way, it was computed that the distance between London and Berwick on the Scottish border was not 260 miles, as previously thought, but 339 miles.
Map making became a respected and indispensable element of the expanding universe. Maps of the New World and the Far East were important fund-raising tools. Deeds to property in "undiscovered" regions were exchanged for monies to finance expeditions to these far-off places. Never mind that native populations already occupied the lands that the Europeans investors purchased.
The accuracy of map making improved greatly with the use of the Ramsden theodolite, a giant surveying instrument used to measure vertical and horizontal angles, equipped with telescopic sights to view long distances. It was accurate to within 5 inches over 70 miles. British surveyors mapped the huge country of India over several decades in the1800's with the use of a theodolite.
Modern surveying instruments have come a long way from the theodolite. Pieces of the Earth that took surveyors years to map are now recorded by cameras high above the Earth in seconds.