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People have been exploring the oceans since prehistoric times, way before they had GPS to help them figure out where they were. In this new episode of SciShow, Hank reveals 6 ingenious ways our ancestors navigated the oceans. Let's go!
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Hank: It's pretty hard to get lost these days, no matter where you are in the world. All you have to do is fire up your favorite navigation app and you're good. Even ships in the middle of the ocean have GPS.

But back before all that technology existed, getting lost was a real danger, especially at sea. To the untrained eye, the ocean looks a whole lot like wet and nothing else. So people around the world independently came up with techniques for squeezing all of the information they could out of what they could see at sea.

Lots of them hit on the usefulness of the stars to tell direction, especially the Sun and Polaris, the North Star. And they came up with nifty devices to pinpoint their location based on the stars, as well as how to find land when it was out of sight. So here are six of the earliest ways people from around the globe mastered the art of navigation, tailored to the different challenges they had to deal with it at sea.

 Stick Chart (1:03)

In Marshall Islands in Micronesia in the Pacific Ocean were first settled around 2,000 years ago. They belong to a larger legacy of navigators who conquered the Pacific with canoes and brainpower. These navigators could find their way between tiny islands throughout the Pacific, and there's some evidence that they made contact with South America long before Europeans did.

They knew a ton about stars, so even though they didn't have magnetic compasses, they came up with what was basically an entire compass made up of knowledge of the night sky. The Marshalees in particular also had an unusual device known today as the stick charts.

Stick charts depict the ocean around one or a few islands in the 1,100 kilometer stretch that is the Marshall islands. But they weren't exactly maps. Instead, they showed what you could feel the ocean doing from a boat.

The Marshallees is bound together straight and curved sticks or fibers to represent swells and currents, the behaviors and patterns of the ocean. Small shells marked where islands were. The charts were actually mainly used as teaching tools. Navigators would memorize all the information in them before ever setting out on a voyage.

Over the past few centuries, much of their traditional knowledge has been lost, but there are people working to revive the art of navigating based on the movements of the ocean.

 The Kamal (2:19)

The Kamal is a simple-looking device. It's basically a rectangular bit of wood and a knotted string. But that's all the sailors needed to figure out their latitude. Compared to European navigators, Arab explorers spent more time out of sight of land on their voyages.

They'd venture farther out because the water is close to the shore of the South Africa were too dangerous to hug the coast. So they needed a good way to keep track of their location which was where the kamal came in. It was probably developed some time after nine hundred C.E. Once sailors got to the right latitude, all they had to do was go east or west until they bumped into the port that they were trying to reach.

To use a kamal, all you have to do is hold the string in your teeth and then hold out the wooden rectangle until the lines matchup with Polaris on top and the horizon on the bottom. The angle between Polaris and the horizon depends on your latitude. It's directly overhead at the North Pole and on the horizon at the equator. So you end up holding the rectangle closer to your face the farther north you are and by measuring the distance from the rectangle to your face you can figure out your latitude. That's what the string is for, it let's you measure the distance from the rectangle to your face.

You can record the latitude of a port by making a Kamal while you're there. You just make a string with the right length and put the rectangle between Polaris and the horizon. Then, to find that latitude again, you sail north or south until the distance from the rectangle to your face matches up with the length of the string.

A Kamal like that only works for one port, so sailors might have had collections of them for getting around. Some, more complicated Kamals were made to be more general measuring devices. Their strings had multiple knots, so you could compare the length of the string with a list of links that correspond to different ports. Or the marks could be at regular intervals, just like centimeter marks on a ruler, with the distance between the knots' corresponding to a known change in latitude. The Kamal was a simple but accurate tool, so much so that it was still in use in the 20th century.

 Cross-Staff (4:08)

The cross staff was another latitude measuring device. The earliest European version is attributed to Levi Ben Gerson, a 14th century Jewish mathematician, though it was probably being used for surveying and astronomy long before that. By 1514, it was being adapted by European sailors so they could use it at sea.

The cross staff works just like the Kamal, and was probably based on it, even though it looks different. It's a long staff marked with degree measurements with a perpendicular sliding crossbar. To use it, you hold the staff up to your cheek and slide the crossbar until the horizon lines up with the bottom edge and either Polaris or the sun at noon lines up with the top edge.

Then you have your latitude just like with a Kamal. As you can probably imagine, looking directly into the Sun to use across staff turned out to be a bit of an issue. A fancier version was eventually developed called the back staff that let people use shadows instead of looking straight at the sun.

A cross staff is most accurate between about 20 and 60 degrees latitude. At higher latitudes, the angles got too big for the human eye to see both sides of the crossbar at the same time. But most of the time, it was a super convenient way for sailors to keep track of their latitude.

 Astrolabe (5:14)

The astrolabe is kinda like a fancier version of the Kamal, or the cross staff. It was probably invented by the Greek scholar Hipparchus, in the second century B.C., when it was used for astronomy. Its use as a navigational tool wasn't recorded until much later in 1481 C.E., by Portuguese sailors traveling down the coast of Africa. It was probably being used for navigation before then though.

The version used for navigation was called the Mariner's astrolabe, and it was another tool for measuring latitude based on the sun and stars. But its advantage over the Kamal and cross staff was that you didn't have to be able to see the horizon to use it. That meant that it worked in fog, or when it was too dark to see the horizon.

A Mariner's astrolabe is a heavy brass disc with a rotating arm in the middle. To use it, a sailor would dangle the disk from a ring at the top so that it would hang perpendicular to the ocean. Then, they would turn the arm until it lines up with the sun or with Polaris. The disk was marked with angle measurements around the edge, so whatever angle the arm pointed to was the altitude of the star. From there, navigators could use math to figure out their latitude.

It might sound easy and accurate, but on a rocking ship's deck, it was actually the opposite of those things. The dangling instrument would swing back and forth too much to get a good reading, massive errors were common, and if you really wanted an accurate measurement, you had to go ashore. Which... iif you're lost, is not easy.

It would have also been hard to use a Kamal or cross step on a rocking ship, but it was probably at least a little easier to get a measurement. Add to that the fact that the other two were easier to make, and you can see why some sailors preferred them.

 Magnetic Compass (6:45)

China was a great naval power in the 15th century, and its greatest navigator was a two meter tall burly Muslim by the name of Zheng He. On the orders of Ming Dynasty Emperor's Zhu Di, he sailed the places like the Red Sea, the Persian Gulf and the eastern coast of Africa in seven voyages, with dozens of huge treasure-filled ships in tow. And he did it using one of China's greatest inventions: the magnetic compass.

The compass had been invented long before Zheng He's time, but his expeditions were among the earliest well-known voyages to use the compass for navigation. Originally, compasses were used for divination. During the Qin Dynasty, more than 200 years BCE, someone noticed that a naturally occurring magnet called a lodestone, would align itself in a particular direction when you laid it down on a fortune-telling board. Eventually, people realized that a lodestone was not pointing to your future or your fate, it was aligning with North and South, and we now know that in general, magnetic materials will line themselves up with Earth's magnetic field.

Early lodestone compasses were shaped like spoons. But then, people figured out that you could magnetize a needle using a lodestone. They started making compasses with iron needles, which are more accurate because they're pointy.

They also realized that if you attached the needle to a piece of wood, or cork and let it float in water, it would spin without friction resisting as much. By his first voyage in 1405, the compass had been perfected enough to lead Zheng He's fleet across the ocean.

 Sunstone (8:07)

The Sunstone was another material with a special property that helps with navigation. About a thousand years ago, ancient Viking texts recorded the use of a magical crystal that could sense the direction of the Sun, even when it was hidden by clouds or below the horizon. For a long time, historians wrote this off as a myth. Sure, the Vikings had magic rocks, they also had trolls and thunder Gods that looks like Chris Hemsworth.

But recent experiments have shown that you can use a rock that would have been available to the Vikings to work out the direction of the sun accurately enough to navigate. It's called Icelandic spars, it's made up of a mineral called calcite and some historians think it was the real Sunstone.

Calcite has a property called birefringence. The mineral has two different indices of refraction, which means that light passing through it gets split in two. Both beams of reflected light form an image, so anything you look at through a birefringence crystal becomes double. Do this with sunlight and one of the images will be brighter than the other. That's because of the way sunlight is polarized: that is the way that the waves lineup in different directions when it passes through the atmosphere.

If you rotate the crystal so it's pointing at the sun, the light coming from the sun will line up so that the two images are equally bright. So if you know how sunstones work, it's pretty easy to use one to pinpoint the location of the sun based on the way that light waves line up, even when you can't actually see the sun.

That said, we don't know for sure that Vikings used calcite for their Sunstones. Calcite crystals have never been recovered from Viking sites, except for a few small fragments. Vikings tended to burn their dead, and calcite is fragile, so even if the Vikings used calcite Sun stones we may never find one.

But researchers did discover a piece of Icelandic spar from an English ship wreck daring dating back to the late fifteen hundreds, which could have been a holdover from the Vikings. So the mythical Sunstone might be real after all, and just another one of the creative ways people came up with it to help them navigate the oceans.

 Outro (9:57)

Thanks for watching this episode of SciShow, which is brought to you by our Patrons on Patreon. if you want to help support this show, just go to, and I want to say thank you to whoever ended up doing animations for this show because I'm sure it was a lot of work. Right at this moment the episode, put your name right here and take credit. Good job!