1497 Voyage | Age of Exploration | Life on Board | Navigation | About John Cabot

Navigation

What technology did John Cabot use to find his way at sea?

The fifteenth-century navigator used a range of equipment to find his way at sea. Most of this technology had come to Europe via the Arab world. Navigational aids that Cabot would have used included almanacs, astrolabes, charts, compasses, cross-staffs, nocturnals and traverse boards. Most of these aids had one thing in common; they measured the angle between objects above the ocean, such as stars or the sun, with the horizon in order to work out the ship's position at sea. Venice was one of the major centres for training navigators. For his time Cabot had skills comparable to an astronaut today.

Measuring the altitude of the sun with an astrolabe in 1545

An astrolabe is used to measure the height of the sun or a star above the horizon. It is difficult to use it on board ship except in very calm conditions

Taking a measurement with a cross staff 1545

Like the astrolabe, the cross-staff measures the angle of a star in relation to the horizon. Although it was less accurate than the astrolabe, it was easier to use on the deck of a ship that was rolling in the waves.

Using a compass an board a medieval ship

The compass is the most basic instrument for finding out the direction in which the ship is travelling. It is believed to have been invented in China.

How did Cabot find his way at sea?

Navigation is working out the direction to take in order to plan a journey across the sea. To navigate the Matthew, Cabot needed to know where he started from (Bristol), where he was at sea and where he wanted to go. In 1491 there was no accurate way to measure longitude (the distance east or west of Greenwich in London), or the speed at which the Matthew was going. He could estimate:

• the time.
• the direction in which he was travelling.
• the latitude (how far he was north of the equator).

The constellations that John Cabot used to navigate at night

By using a an instrument called a nocturnal, Cabot could measure the position of Ursa Major or Ursa Minor in relation to the North Star (Polaris) to work out the time at night.

Medieval Maps

What maps were there?

The world map of Juan de la Cosa 1500 was made in A.D. 1500 by a Spanish cartographer of the same name. He sailed with Christopher Columbus on one of his voyages to the Americas.

If the map is genuine and it probably is, it shows us that:

• In 1500, people knew the shape of the coastline and islands of the continent of America from the Caribbean region to Newfoundland.
• This Spanish geographer accepted that the English had already been there. There are five English flags shown along the northern coastline and a stretch of water marked "Mar descubierta por inglese" ("sea discovered by the English").

This suggests that, if the marking is accurate, Cabot might have landed on the main American Coast. If so, he reached it a year before Christopher Columbus.

A matter for debate is whether la Cosa used a map (now lost) made by Cabot in order to draw his outline of the North American continent.