Sailors navigating the open seas made use of several techniques to determine their location, including staying in sight of land and understanding of the winds and their tendencies. Obviously the navigational practices centuries ago differ vastly from what we do have now but the technical know how even then was key. Navigation can simply be described as the art of getting from one place to another, safely and efficiently. Navigators then did not have charts but instead used lists of directions. When they did venture out of sight of land, they able to determine their latitude (north/south direction) by observing the height of the sun during the day and the North Star at night.
EARLY NAVIGATIONAL TOOLS
Determining latitude can be accomplished relatively easily using celestial navigation. In the Northern Hemisphere, mariners could determine the latitude by measuring the altitude of the North Star above the horizon. The angle in degrees was the latitude of the ship.
One of the earliest human-made navigational tools used to aid mariners was the mariner's compass, which was an early form of the magnetic compass. Early mariners thought the mariner's compass was often inaccurate and inconsistent because they did not understand the concept of magnetic variation, which is the angle between true north (geographic) and magnetic north. It was primarily used when the Sun was not visible to help identify the direction from which the wind was blowing.
During the mid-thirteenth century, mariners began realizing that maps could be helpful and began keeping detailed records of their voyages. This is how the first nautical charts were created. These first charts were far from accurate, but were considered valuable and often kept secret from other mariners. There was no latitude or longitude labeled on the charts, but between major ports there was a compass rose indicating the direction to travel.
A sextant is a measuring instrument generally used to measure the angle of elevation of a celestial object above the horizon. Making this measurement is known as sighting the object, shooting the object or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at noon to find one's latitude. Held horizontally, the sextant can be used to measure the angle between any two objects, such as between two lighthouses, which will, similarly, allow for calculation of a line of position on a char.