How was longitude discovered?

Cracking the Code of the Seas: The Epic Tale of How We Found Longitude

Imagine sailing the vast oceans for months, knowing exactly how far north or south you were, but having absolutely no clue how far east or west. That was the reality for mariners for centuries! They could figure out their latitude easily enough, but longitude? That was the puzzle that launched a thousand shipwrecks. This wasn’t just about getting lost; it was a matter of life and death, and solving the “longitude problem” became an obsession.

Longitude, the east-west position on our planet, had been a head-scratcher since the days of ancient Greek stargazers like Eratosthenes and Hipparchus. They grasped the basic concept – longitude is linked to time – but turning that idea into a practical tool? That was the tricky part. Ptolemy, a big name in 2nd-century mapmaking, did his best, but early longitude estimates were often just educated guesses based on travelers’ tales. Not exactly reliable!

One of the earliest ideas involved lunar eclipses. The thought was simple: everyone on Earth sees a lunar eclipse at the same moment. So, if you could compare the local time of the eclipse in two different places, you could figure out the time difference, and boom – longitude! Sounds good in theory, but eclipses aren’t exactly an everyday occurrence, and getting accurate measurements at sea? Forget about it.

Then came the lunar distance method, which gained traction in the 1500s. This involved measuring the angle between the moon and certain stars. By comparing these angles with predictions in astronomical tables, you could (in theory) figure out the time at Greenwich, England – the prime meridian. Compare that to your local time (based on the sun’s position), and you had your longitude. Johannes Werner wrote about it back in 1514. The method got a boost in 1767 when Astronomer Royal Nevil Maskelyne published the Nautical Almanac, providing tables of lunar positions. Still, it was a complex process, requiring serious skill and calculation. Not exactly user-friendly for the average sailor.

And let’s not forget Galileo! Back in 1610, when he spotted Jupiter’s moons, he thought he’d cracked it. He figured their predictable orbits could be used as a kind of universal clock. The problem? You needed a stable telescope to see those moons clearly, and “stable” and “ship at sea” don’t exactly go hand-in-hand.

By the 1700s, with global trade booming and naval power becoming crucial, the pressure was really on. The British government stepped in with the Longitude Act of 1714, offering a king’s ransom – a whopping £20,000 – for a solution that worked. That’s like winning the lottery today! They even set up the Board of Longitude to judge the entries.

Enter John Harrison, a clockmaker who wasn’t afraid to think differently. He believed the answer wasn’t in the stars, but in a really, really good clock. A clock that could keep perfect time, no matter how rough the seas got. He called it a chronometer.

Harrison’s first attempt, H1, was a beast of a machine finished in 1735. He kept tinkering, building H2 and H3, each an improvement on the last. But it was H4, completed in 1759, that was the game-changer. It looked like a big pocket watch, but it was incredibly accurate.

The real test came in 1761, on a voyage to Jamaica. H4 nailed it, proving longitude could be determined with incredible precision. You’d think Harrison would be showered with riches and praise, right? Wrong! The Board of Longitude was skeptical and dragged their feet. It took the intervention of King George III himself to finally get Harrison a fair chunk of the reward in 1773. Talk about a bureaucratic headache!

Harrison’s chronometer changed everything. The idea was simple: set your chronometer to Greenwich time, find your local time by looking at the sun, and the difference between the two tells you your longitude. Every hour of difference equals 15 degrees of longitude. Easy peasy!

The lunar distance method hung around for a while, especially when chronometers weren’t available or reliable. But ultimately, Harrison’s invention won out. Today, we have GPS making longitude a breeze, but we owe a huge debt to the folks who wrestled with this problem for centuries. It’s a reminder that even the most impossible challenges can be overcome with a little ingenuity and a whole lot of persistence.