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À la carte: Nova Scotia’s treacherous waters | Lights in the darkness | Wherefore the weather in Nova Scotia? | Preserving our shipwreck heritage | Shipwreck diving — The thrill of discovery | Advances in navigational technology | From the CG Archives

In today’s world, it is not unusual for an outdoor sports enthusiast to take a GPS (Global Positioning System) device, a watch-mounted compass and detailed maps on a weekend backcountry excursion. But can you imagine the challenges faced by early explorers who had to cross uncharted waters with little more than the stars to guide them?

When intrepid Vikings made some of the first visits to North America 1,000 years ago, they largely relied on the sun, stars and wind for navigation. Since then, tremendous developments in navigational aids have kept pace with the desire to explore further and further afield. The following are some of the significant innovations that helped guide seafarers on the open ocean and decrease the risks of becoming a shipwreck casualty on potentially perilous shores.

MARINER’S COMPASS (13th century)
A crude version of a magnetic compass, the mariner’s compass was one of the earliest man-made navigation tools. To construct the device, a sailor would rub an iron needle against a lodestone, stick it in a piece of straw and set it afloat in a bowl of water. The magnetized needle pointed to magnetic north, but since early mariners did not understand the difference between true north and magnetic north, the compass was considered inconsistent. Until this difference was understood several centuries later, the compasses were not as useful to navigators as they are today.

LEAD LINE (13th century)
This long line of rope with a lead weight thrown over the side of the ship served two purposes: first, the weighted line had markings to measure the water depth. Second, the weight also served to collect a sample of the bottom to indicate what the seabed was like. Such records resulted in a method that allowed sailors to navigate between different depths based on the type of bottom encountered.

ASTROLABE (13th to 16th centuries)
A tool for measuring latitude, the astrolabe dates back more than 2,000 years to ancient Greece, where it was originally used to find the altitudes of celestial bodies. However, it was likely introduced in Europe only by the 11th century. European usage became widespread in the 13th and 14th centuries but peaked in the 15th and 16th centuries. The astrolabe determined latitude, or the relative north-south position, by measuring the angle between the horizon and Polaris, the North Star. The North Star was useful for measuring latitude because it is less than one degree from the north celestial pole (the point in the sky directly above the geographic north pole). The heavy astrolabe was awkward and difficult to use aboard ship, but when taken ashore it helped discern the approximate latitudes for newly discovered lands.

CHIP LOG (16th century)
At this time, mariners still lacked a method of measuring longitude, or the east-west location, but the chip log (a sort of speedometer) helped navigators calculate how far they’d traveled east-west. The chip log consisted of a light rope knotted at regular intervals and attached to a weight. The weight was tossed astern, dragged in the water, and a sailor counted the knots pulled overboard for a specific length of time (using an hourglass timer) to determine how fast the vessel was moving (thus the use of the term "knots" to describe sailing speed). Since the navigator could measure the beginning and end latitudes during a day’s travel and now knew approximately how fast the ship was traveling, he could also determine the distance traveled and estimate the ship’s east-west position.

MERCATOR PROJECTIONS (16th century)
In 1569, the Flemish cartographer Gerardus Mercator published the first maps to accurately represent the Earth’s spherical surface. Prior to this, mariners experienced great problems in navigation since maps based on a flat representation of the Earth had increasingly large errors as the area to be mapped expanded. This was particularly important to explorers crossing huge expanses of open ocean. Mercator’s solution involved mathematical formulae that allowed him to draw the normally converging lines of longitude as parallel lines on the map, producing a grid of latitude and longitude. To correct for the east-west variation in longitude that grows with latitude, Mercator spaced the parallels of latitude in a corresponding ratio, drawing them further apart as they approached the pole.

CHARTS OF MAGNETIC VARIATIONS (18th century)
Charts showing the magnetic variation between magnetic north and true north in different parts of the world became available in 1701. This made the magnetic compass an even more valuable tool for navigation.

SEAGOING CHRONOMETER (18th century)
Although the concept of longitude (the converging lines on the globe extending between the poles) had been understood for centuries, a single, simple problem prevented mariners from determining their longitudinal position at sea. To calculate longitude, one needs to know the time at a reference point, such as zero degrees longitude (what would become the Prime Meridian in Greenwich, England), and the time at the ship’s location (each one hour difference represents 15 degrees of longitude). On a ship, the local time could be estimated by the sun’s position, but the reference time at zero degrees longitude also had to be maintained on the ship.

Reliable pendulum clocks existed at the time, but the motion of a ship plus the variation in temperature and humidity rendered them useless. Many countries began offering prizes for developing a sea-worthy clock. In 1764, John Harrison won the British prize for his seagoing chronometer, which was accurate to one-tenth of a second a day. Captain James Cook used the chronometer to circumvent the globe, and his resulting calculations of longitude proved accurate to within 12 kilometres. The charts Cook produced with the help of the chronometer forever changed the face of navigation.

GYROSCOPIC COMPASS (20th century)
The gyroscopic compass was introduced in 1907 by inventor Elmer Sperry. The movement of the compass depends on a gyroscope, a free-spinning disk mounted on a base, so that the disk remains in a fixed position no matter what direction the base is moved. The gyroscope is aligned on a north-south axis, and the compass points to true north rather than magnetic north. This made the compass a more reliable navigational device, and Sperry’s gyroscopic compass was adopted by the U.S. Navy in 1911, playing a major role in the First World War.

RADAR (20th century)
RADAR is an acronym for radio detecting and ranging. Its beginnings came in 1887 when a German physicist named Heinrich Hertz began experimenting with radio waves, learning that some materials reflected radio waves while others allowed the waves to pass through. In the 1920s and 1930s, between the two World Wars, scientists around the globe were researching the use of radio waves to detect objects. The first practical radar system was produced in 1935 by British physicist Robert Watson-Watt. Radar became a very important instrument during the Second World War because of the need to locate enemy submarines. By transmitting electromagnetic energy towards suspected objects and observing the resulting "echo," the presence and position of objects such as submarines or aircraft could be detected, as well as their size and shape, speed and direction of movement. During the war, it was discovered that radar could be used to study weather, another boon to sailors and to the general public.

GLOBAL POSITIONING SYSTEM (20th century)
The most advanced navigational system today is the Global Positioning System, or GPS. Operated by the U.S. Department of Defense, GPS was developed in the 1970s and consists of 24 satellites that allow us to determine latitude and longitude within 10 metres of accuracy. Each satellite broadcasts a signal and a precise time message that are captured by a GPS receiver (such as a hand-held unit you can take on hiking trips). The signal takes a short but measurable amount of time to reach the receiver, and the difference between the time the signal is sent and received, multiplied by the speed of light, allows the GPS receiver to automatically calculate the distance to the satellite. The distances to four separate satellites are measured to determine the receiver’s exact location on Earth.

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