Navigating With or Without a Compass

Navigation is the means by which a person can pinpoint their geographic location and then accurately determine where they need to travel to reach their intended destination. Although this can seem simple, there’s an art to the science.

The first sailors followed the coastline, keeping land in sight, as this was the safest way to avoid getting lost at sea. The Greeks may have also used clouds and smell as navigational clues, since weather tends to form over landmasses, and odors can drift far across the ocean. Polynesians would watch the pattern and color of the waves, which when observed with expert eyes can indicate the direction of land. Sailors in ancient cultures also used the reliable nature of trade winds and currents to push them in the right direction.

On land, physical features are good points of reference for determining distance and position. Natural landmarks like mountains, rivers, and lakes can be used as geographic coordinates. But when civilizations began to cross long distances over deserts and oceans, a more precise method for calculating fixed positions became necessary. Eventually, a grid system was developed, which marked latitudinal and longitudinal lines across a global map.

Latitude measures the distance from the equator, delineated by east-west lines that run parallel to the equator on a map of the world. These latitudinal lines are called “parallels” and are measured in degrees. For example, the value of the parallel at the equator is zero degrees latitude, with the North Pole measuring 90 degrees north, and the South Pole measuring 90 degrees south.

Longitudinal lines are like latitudinal lines, except that they extend north to south, running parallel to the prime meridian, which divides the world into the Western and Eastern Hemispheres. Longitudinal lines are called “meridians” and, like latitudinal lines, the distance between each line is called a degree. On average, one degree of longitude or latitude measures approximately sixty-nine miles. There are 360 degrees of longitude around the globe and 180 degrees of latitude. Each degree, of either longitude or latitude, can be divided into 60-minute units, which can further be divided into 60 seconds. These units, however, don’t correspond to measurements of time.

The lines of longitude and latitude form a grid pattern. The point where a parallel and a meridian intersect is called a coordinate, which can be used to determine an exact location on Earth. For example, the latitude coordinate for New York is written as 40°42′ N, which translates to 40 degrees and 42 minutes north of the equator. The longitude coordinate is 74°00′ W, which means it’s 74 degrees and zero minutes west of the prime meridian.

METHODS OF NAVIGATION

Humans have been developing navigational tools for thousands of years. Ancient civilizations used a variety of navigational systems to guide their way, some of which are still being used to this day.

DEAD RECKONING

While the term may seem ominous, dead reckoning is simply a method of wayfinding that doesn’t depend on a clear sky and being able to see the stars. Rather, it involves determining a geographic position by noting a previous location, called a “fix,” and then using the velocity and direction traveled to estimate the current location. Dead reckoning is also used in nautical and aerial navigation, but lacks precision given uncontrollable variables like current and wind, which can shift the location of any point, making it difficult to find a fix. Since watercraft and aircraft are constantly in motion, this increases the challenge of calculating any given location with accuracy.

SUN AND STARS

One of the most common navigational methods humans have used, celestial navigation, involves using the positions of the sun, stars, and moon to find north and south. The most basic navigational method was simply to use the position of the sun to find east and west. The Phoenicians named east and west Asu (sunrise) and Ereb (sunset), the eponymous roots for the eastern and western continents Asia and Europe. Celestial navigation also requires a familiarity with the constellations, the positions of which are dependent on the time of year and whether you happen to be looking up at the night sky in the Northern or Southern Hemisphere.

For more accurate measurements, ancient cultures would employ sophisticated instruments to help determine latitude, like the Arabian kamal, the astrolabe used by sailors in the Middle Ages, or the gnomon used in China. A sextant is another useful tool in celestial navigation, in that it measures with precision the angle between objects in the sky and the horizon, which helps to determine a location with accuracy. A clock and an almanac are also necessary for the celestial navigator, used in tandem to establish the location of the constellations during a specific time of year and time of night.

COMPASS

The ancient Chinese may have been the earliest civilization to use the compass—an instrument with a needle that points toward magnetic north, which is affected by the earth’s magnetic field. Because the earth’s magnetic poles aren’t fixed on its axis, magnetic north will vary depending on your location. True north is earth’s true geographic north. To give an accurate reading, most modern compasses will account for the magnetic declination between the two norths.