200 BC: The compass
Developed in ancient China, the compass remains one of the oldest navigation devices. Modern electronic compasses can adjust for differences between magnetic north and true north.150 BC: The astrolabe
These devices were first developed in ancient Greece and were used to predict the positions of the sun and moon, and to calculate local time based on local latitude. The type shown at right is a “nocturnal” from the 1500s.1656: The pendulum clock
First developed by Christiaan Huygens, precise chronometers using variants of the pendulum start to be used as standards for determining longitude.1730: The sextant
This device uses a combination of mirrors to determine the relative angle between two celestial objects. Sighting Polaris gives latitude. It can also measure the lunar distance between the moon and other objects and can be used to determine Greenwich Mean Time, and thus longitude.Early to mid 1900s: Radio direction finders
With the invention of the airplane, transportation speeds went from a few dozen knots aboard ships to several hunderd knots for aircraft. Rapid navigation equipment became essential.
First attempts at using radio beams for guidance and navigation proved unreliable. Amelia Earhart used an antenna like the Bendix unit, left, in an attempt to locate Howland Island.
Later, innovations such as LORAN (long range navigation, 1942) enabled a position to be fixed within 10 miles in all weather. Introduction of VHF Omni-Directional Radio Range systems (VOR) in 1946 increased precision to within 300 feet. An early VOR receiver is shown at right.1949: Atomic clocks
Built by the National Bureau of Standards, the first atomic clocks were less reliable than quartz watches of the day, but proved the concept. Accuracy came when cesium clocks were developed in the 1950s in the United Kingdom. In 2014, the U.S. National Institute of Standards and Technology started an atomic clock expected to drift by less than one second in 300 million years.1978: Navstar GPS
Developed during the Cold War to ensure accurate missile targeting, the U.S. military’s GPS was opened for civilian use in 1983 after a Korean Air Lines 747 was shot down near Sakhalin, USSR, for straying near restricted Soviet air space. Left is an rtist’s rendering of a Block II GPS Satellite. Right is a 1988 Magellan NAV-1000 GPS Receiver.Today: Embedded navigation
Navigation aids have become commonplace, with GPS and cellular tower telemetry, interactive maps, gyrocompasses and self-setting chronometers — linked to national standard clocks — built into phones, tablets and vehicles.
