Learning Objective:
Students will learn about latitude and longitude and why these concepts are so important to navigation. In the activity at the end of this lesson plan, students will develop practical mapping skills and improve their understanding of coordinates by practicing finding points using latitude and longitude.
The “longitude problem” was the greatest scientific dilemma of the eighteenth century and had been for centuries prior. Through trade, conquests, colonialism, and war — profit was made on the sea. Sailors throughout the ages of exploration were lost at sea, and the fortunes of nations hung in the balance on a resolution to the problem.
While latitude can be determined by any sailor worth his or her salt by the length of the day, the height of the sun, or guide stars on the horizon, longitude is tempered by time.
Because of the Earth’s rotation, the difference in longitude between two locations is equivalent to the difference in their local times: one degree of longitude equals a four-minute time difference, and 15 degrees is equal to one hour (making 360 degrees, or 24 hours, in total).
Since there is no naturally occurring zero point, or prime meridian, for historical and political reasons, today, it runs through Greenwich, near London in the United Kingdom. Beginning in 150 AD with Ptolemy, who plotted longitude to run through what is now the Canary and Madeira Islands off the coast of North West Africa, cartographers throughout history placed it in a variety of points around the globe from the Azores, Rome, Copenhagen, and Jerusalem to St. Petersburg, Pisa, Paris, and even Philadelphia.
If sailors lacked visible reference points in the skies or on land, it made finding their position very difficult. Historically, to keep track of their position, mariners used dead reckoning, the act of calculating a current position by using a previously known position and mathematically updating it based on estimated speed, direction (or heading), and elapsed time.
For common trade routes, especially coastal routes, not knowing longitude was not a major problem, but as trade routes and imperial ambitions expanded, monarchs, merchants and investors sought improved methods of navigation that might increase the reliability of their profits. Western imperialism and commercial expansion underpin the history of longitude.
Before reliable clocks, a rolling ship could slow down, speed up, or stop a clock all together. Changes in temperature could thin or thicken a clock’s lubricating oil — making the metal parts expand or contract — both with disastrous results. A rise or fall in barometric pressure or subtle variations in gravity from one latitude to another could cause clocks to gain or lose time. Early explorers like Vasco de Gama and Ferdinand Magellan got to where they were going by pure luck, and many sailors throughout time died en route due to lack of supplies, scurvy, or storms at sea if voyages took longer than expected because of an inability to navigate properly.
In 1714, the English Parliament offered a king’s ransom (£20,000 or several million today) to anyone who could provide a “practical and useful” means of determining longitude. While scientists in both hemispheres looked to the stars for answers, one man imagined a mechanical solution. John Harrison, an English clockmaker, built the chronometer – virtually friction free, required no lubrication or cleaning with materials impervious to rust, and the rest is history!
Initially marine chronometers were very expensive, so roll out was slow. Future clockmakers simplified designs and made them cheaper and easier to produce, with more ships using them at the start of the 1800s. The tools developed in the eighteenth century – astronomical tables, sextants, and timekeepers – remain essential equipment for ships today as back-up technologies.
Why Are Latitude and Longitude Important?
- We use them every day to navigate with maps and GPS – think of pilots and ship captains who rely on these coordinates to navigate planes and ships.
- They help meteorologists track weather systems and natural disasters, and emergency teams use GPS coordinates to locate affected areas during and after natural disasters.
- Scientist use them to study climate patterns.
- Longitude positions determine time zones.
Key Concepts:
Latitude (Lines Run East-West)
- Latitude lines measure distance north or south of the Equator (0° latitude).
- They are parallel lines that run horizontally across the globe.
- Examples: The Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S).
Longitude (Lines Run North-South)
- Longitude lines measure distance east or west of the Prime Meridian (0° longitude).
- These lines converge at the North and South Poles.
- Examples: The Prime Meridian (0°) and the International Date Line (180°).
Common Misconceptions About Latitude and Longitude
- Thinking that latitude lines are vertical and longitude lines are horizontal. It’s the opposite.
- Assuming coordinates are measured from the poles rather than the Equator and Prime Meridian.
- Believing the Equator is the hottest point on Earth. A variety of factors, including altitude and ocean currents also affect temperature.
Ways to Remember the Difference
- Latitude: “Lat is flat”. Visualize these lines running parallel across the equator like layers on a cake.
- Longitude: Imagine cutting an orange into wedges; longitude lines are the long, curved lines connecting the North and South Poles.
Activity: Coordinate Treasure Hunt to Teach Latitude and Longitude
Objective:
Students will develop practical mapping skills and improve their understanding of coordinates by practicing finding points using latitude and longitude.
Materials:
- World maps or globe
- Pre-made coordinate cards
- “Treasure” markers (stickers, tokens, or small prizes)
Steps:
- Distribute maps to each student or group.
- Give students coordinate cards representing famous landmarks throughout the world.
- Have students plot the coordinates on their maps. Each correct answer earns a “treasure” marker.
- Bonus Challenge: Have students create their own coordinate clues for classmates to solve.
Additional Resources:
“Longitude found: the story of Harrison’s timekeepers,” Royal Museums Greenwich, .
Royal Greenwich Observatory Archives Primary Sources, Cambridge Digital Library,
Dava Sobel, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time (1995).
