Early Magnetic Compasses Bore Little Resemblance to Their Modern Counterparts

Today, magnetic compasses are so ubiquitous that we just call them “compasses.” They contain a magnetized needle that naturally lines up with the Earth’s magnetic field, so the ends point to magnetic north and magnetic south (moving targets that are  fairly close to true north and true south, but that can lead to errors when traveling very far north or very far south).

Scientists don’t know for sure who made the first compass, but they believe the first compasses to be used for navigation came from 11th- or 12th-century China. The first European usage of a compass was recorded at the end of the 12th century. These early prototypes used lodestones (pieces of naturally-occurring magnetic ore) or needles magnetized with lodestones that were then attached to sticks or corks so they could float in water. 

At first, magnetic compasses were used primarily as backup navigation aids, but as engineers got more savvy, compasses became more reliable. By the 13th century, the compass’s design had graduated to a magnetized needle mounted on a pin at the bottom of a bowl. In time, a directional card with the 32 principal points of direction began to be mounted beneath the needle. The design of the card itself evolved, too: The north point was first marked by a spearhead and a “T” for the Latin word Tramontana, meaning “the north wind.” Around 1490, these symbols were replaced with a fleur-de-lis, which is still commonly seen on compasses today.

Astrolabes Weren’t Just Used for Navigation

The concept of an astrolabe, a device used to measure the positions of celestial bodies, dates back to ancient Greece in the third or second century BCE — although its exact origin is unclear. By the ninth century CE, astrolabes were highly developed and utilized in Arabic cultures. The devices made their way back to Europe in the 12th century, and the mariner’s astrolabe was a standard piece of navigational equipment by the end of the 15th century, just in time for the Age of Exploration.

Astrolabes are used to determine the locations of celestial bodies relative to the user. A disk called a “mater” holds a series of smaller rotating and sliding disks — one with Earth’s latitude lines and another with well-known constellations and stars. A straight “rule,” or bar, spins around that, and a sight helps determine the altitude of the sun or another star that can then be used as an anchor point. Astrolabes often came with specific plates that corresponded to the different latitudes of certain large cities, because the sky’s geography is affected by one’s latitude.

While these devices were very useful for navigation, it wasn’t their only claim to fame:  In the Islamic world, they helped determine prayer times and the direction of Mecca. During the Middle Ages in Europe, they were consulted to help with decision-making, much like modern horoscopes. And more mundanely, they could also be used for making topographical surveys.

Vikings May Have Used Crystals to Navigate

The Vikings, a group of seafaring Scandinavian warriors, were also skilled ocean navigators. They began to populate Iceland — around 500 miles from their native Norway — in about 900 CE, even eventually reaching North America. The specifics of their navigation techniques are somewhat mysterious, but recent research indicates they may have used crystals.

Because they sailed their longships in the far North Atlantic, Viking travelers benefitted from up to 24 hours of continuous daylight, but they encountered a lot of fog, too. Ancient Norse literature mentions “sunstones,” stones that helped their holders find the sun — and scientists now think these may have really existed. In 2011, researchers used calcite crystals to pinpoint the location of the sun within 1 degree. It’s not magic, although it sounds like it: Through polarization, crystals can show sunlight patterns that can’t be seen with the naked eye.

Another study from 2014 suggests these crystals may have been used in conjunction with a sun compass. Researchers simulated 3,600 trips between Norway and Greenland at the spring equinox and summer solstice, two dates marked on a disc believed to be a component of a sun compass. They found that by checking the crystals every few hours, the computer-generated voyages successfully reached Greenland 92% of the time.

That study hasn’t been replicated in the real world yet, but it offers some clues to how Viking navigators were able to navigate without the use of magnetic compasses or astrolabes.

Navigators Knew the Earth Was Round Earlier Than You Might Think

There’s a persistent myth that Christopher Columbus “proved” the Earth was round in the 15th century during his voyage from Europe to the Americas, but he was many centuries too late. In fact, formally educated people knew the world wasn’t flat starting way back in the third century BCE, while scientists and mathematicians may have known as early as the sixth century BCE. Columbus’ surprise landing in the Americas had nothing to do with thinking the Earth was flat — he just thought the global circumference to be smaller than it is and believed he’d end up in Asia. This tenacious myth comes from a highly embellished 1828 biography of Columbus written by Washington Irving, better known for fictional works such as “The Legend of Sleepy Hollow” and “Rip Van Winkle.”

Like the aforementioned scientists and scholars, mariners were aware of the world’s roundness very early on. Sailors observed that when viewing distant ships, the tops of sails and masts were visible before the decks and hulls of the vessels to which they were attached. And as they traveled to different points of the Earth, they also noted being able to see different constellations. Celestial navigation would have been pretty difficult otherwise.