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 fortunate to have GPS to help us navigate. However, GPS has only been around for a few decades, so 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 patterns of the stars. Sailors knew that the constellations, or groups of stars in the sky, appeared to change with the changing seasons in a certain pattern. This knowledge and their observations of patterns helped them find their way across vast distances.

They used a tool called a sextant that 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 needed another piece of equipment, something that could keep accurate time at sea. 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. A chronometer was the first tool to keep real time at sea.

Pendulum clocks had been around for hundreds of years but they could not keep accurate time on ships. Ships are subject to the movement of the ocean waves, which caused the pendulum to swing inaccurately. John Harrison, an English carpenter, solved that problem with the chronometer.