Speed and Direction Higher_02

Fortunately, the ship is equipped with a system that tells them where they are. The system is called GPS, short for Global Positioning Satellites. GPS uses Earth-orbiting satellites to tell us our position anywhere on Earth within a few meters. Today, we are lucky to have GPS to help us navigate, but GPS has only been around for a few decades. How did sailors navigate before they had GPS?

It was not until the 1700s that finding one’s location at sea became possible. Until then, sailors observed the stars. Sailors knew that the constellations, or patterns of stars in the sky, appeared to change with the changing seasons. They used this knowledge and observations of patterns to help find their way.

They used a tool called a sextant. It measured the distance of stars above the horizon. Sailors could recognize specific stars based on the constellations they were a part of. Sailors used a sextant and observation of the stars to determine how far north or south they were but not east and west. To know the distance east and west, sailors need another piece of equipment: a chronometer. Imagine not knowing exactly where you were in the middle of the ocean!

The invention of the chronometer (sounds like krawn-AW-meter) solved that problem. Chronometers were the first tools to keep real time that could be used at sea.

Pendulum clocks had been around for 100 years, but none could keep accurate time on ships. Ships are subject to the movement of the ocean waves, which causes the pendulum to swing inaccurately. John Harrison, an English carpenter, solved that problem with the chronometer.