Navigating by the stars

The dangers of sailing

Today, our phones connect to satellites allowing us to find our way almost everywhere on earth, but long ago, sailors did not have that option. There were no maps of the oceans. Sailors risked their lives every time they set sail. Storms could break their masts, wind could shred their sails, and rough seas could wash men overboard. Hidden reefs could tear a hole in the hull (bottom) of their ship. Giant waves could sink them. A lack of wind to push them along could leave them stuck in the middle of the ocean. On top of all these risks, they could very easily become lost. Any of these could mean a ship would wander about until the food and water ran out.

Sailors couldn't predict the weather, winds or tides, but they did learn how to navigate. Before this, they would stay within eyesight of the coast, and therefore, know where they were based upon the land formations such as cliffs or mountains. There are no landmarks in the open ocean, so sailors learned to use the stars, including our sun, and Earth's magnetic field to navigate, and that meant they could cross oceans.

Early compasses

Early compasses were notoriously unreliable. They would sometimes lose their magnetic charge, and the ship's motion on the water sometimes made it difficult to get a steady reading. Compasses also point at magnetic north, not true north, so as they sailed around, magnetic north changed in relation to true north. Though many were working on a better compass, for the time being, using Earth's magnetic field was only going to help so much. The North Star, however, was always located at true north.

The north star

The North Star, also known as Polaris, is located directly over the North Pole, appearing fixed in the night sky. Because of Earth's spin, all of the other stars appear to travel in circular arcs around the North Star. It serves as a reference point that allowed sailors to find their way. To know their location, sailors needed to know their latitude and longitude. Sailors only had to measure the angle of elevation of the North Star and they could figure out their latitude on the map because the angle of elevation of the North Star is equal to one's latitude on a map. Determining longitude was a more difficult task requiring an extremely precise clock, but that problem was soon solved, too.

Locate polaris

The North Star, or Polaris, is in a constellation known as the Little Dipper or Ursa Minor.

Photo by Ashley Dance; Wikimedia Commons

This time-lapse photo shows the other stars rotating around the North Star during a typical northern hemisphere night.