Reading 2

Unit 10- Reading 2

Page 166

Navigation

METHODS

There are several different branches of navigation, including but not limited to the following. Click on terms to see individual entries:

• Celestial navigation: using observed positions of the sun, moon, stars, and sometimes planets to navigate at sea

• Pilotage: using visible natural and man-made features such as human-made sea marks and beacons, sometimes with the aid of a nautical chart, or map of marine and coastal areas

• Dead reckoning: using course and speed to determine position

• Off-course navigation: deliberately aiming to one side of the destination to allow for variability jn the heading (direction)

• Electronic navigation: using electronic equipment such as radios and satellite navigation systems to follow a course; e.g., Electronic Chart Display and Information System (ECDIS), an electronic alternative to printed nautical charts

• Position fixing: determining current position by visual and electronic means

• Collision avoidance using radar

HISTORY

Navigation is the science of accurately determining one’s location and then planning and following a route.

The earliest form of navigation was land navigation. This relied on physical landmarks to chart the journey from one place to another. Away from land, one must use other markers in order to navigate successfully. One modern way to do this is to keep track of one’s position using longitude and latitude. These are two kinds of imaginary lines drawn on maps or globes representing the Earth.

Latitude is distance north or south of Earth’s equator. Longitude is distance east or west of the Greenwich Meridian, an imaginary line that runs from the North Pole to the South Pole and through Greenwich, England.

Marine navigation may have begun when prehistoric people attempted to guide a vessel, perhaps a log, across the water using familiar coastal landmarks.

In the pre-modern history of human migration and nautical exploration, a few peoples have excelled as seafarers. Prominent examples include the Polynesians and the Micronesians of the Pacific Ocean. The Polynesian navigators routinely crossed thousands of miles of open ocean to reach tiny islands. They used only their own senses and knowledge of the sea that was passed down from generation to generation.

In eastern Polynesia, navigators memorized extensive catalogs of information in order to help them navigate at various times of day throughout the year. These catalogs included the following kinds of information:

• The motion of specific stars, and where they would rise and set on the horizon of the ocean

• The weather

• Time of travel

Wildlife species (some species assembled at particular locations)

• Ocean swells and how they would affect the crew

• The color of the sea and sky, especially how certain types of clouds would assemble at particular locations above some islands

• The angle at which navigators should approach a harbor

These sets of information were kept as guild secrets. Generally, each island maintained a guild, or group, of master navigators who had very high status.

In times of famine or difficulty, only they could trade for aid or evacuate people. The guild secrets were almost lost. Fortunately, one of the last living navigators taught them to a professional small-boat captain so that he could write them down. The captain recorded these secrets in book form, creating an early navigator’s manual.

Ancient sailors used celestial bodies (that is, objects in the night sky) to steer by. For example, in the Northern Hemisphere one can look for the constellation (group of stars) known in English as the Big Dipper. Sailors could use the Big Dipper to find the North Star, which tells which way is north.

But celestial navigation as it’s known today was not used until people better understood the motions of the Earth, sun, and stars. Nautical charts were developed to record new navigational and piloting information for other navigators. The development of accurate celestial navigation allowed ships’ crews to better determine position.

The most important instrument for nautical navigation was the navigator’s diary. These diaries contained crucial information.

They often became trade secrets because they enabled safe travel to profitable ports.

One problem with all early forms of navigation was that they required voyagers to be able to see either land or sky. By the year 300, the magnetic compass had been invented in China. Sometime between 850 and 1050, they became common navigational devices on ships.

Magnetic compasses allowed sailors to continue sailing a course even when the weather limited the sky’s visibility. This instrument also allowed the development of dead reckoning. Dead reckoning can be used to navigate when landmarks are out of sight, although it stilt requires people to accurately know their location from time to time.

Arab navigators in the 9th century developed a celestial navigation tool called a kamal.

A kamal consists of a wooden rectangle and a length of rope with evenly spaced knots. Navigators used this instrument to measure the angle of a particular star above the horizon, which allowed a navigator to determine the ship’s latitude. Arab navigators were very successful with using this device, establishing trade networks from the Atlantic Ocean and Mediterranean Sea to the Indian Ocean and China Sea.

Navigators from India and China later adopted use of the kamal. A limitation of the kamal is that it’s mainly useful only in lower latitudes, or regions relatively near the equator.

After Isaac Newton published the Princlpia in 1687, navigation was transformed. Mathematics was applied to the study of nature, and the entire world was measured using essentially modern latitude instruments and the best available clocks. In 1730, the sextant was invented.

A sextant uses mirrors to measure the altitude of celestial objects in relation to the horizon.

In the late 19th century, Nikola Tesla invented radio. Soon, radio beacons and radio direction finders were providing accurate tand-based fixes, even hundreds of miles from shore. This system lasted until modern satellite navigation systems made it obsolete. Around 1960, LORAN was developed.

This measured how long a radio wave took to travel between antennas at known locations. These measurements allowed travelers to fix positions. The equipment could then locate geographic positions to within a half mile (800 m). At about the same time, TRANSIT, the first satellite- based navigation system, was developed. It was the first electronic navigation system to provide global coverage.

In 1974, the first GPS satellite was launched.

GPS systems now give accurate locations with an error of only a few meters. They also have precision timing, giving time measurements with an error of less than a microsecond (one millionth of a second). GLONASS is a positioning system that was launched by the Soviet Union. It relies on a slightly different model of the Earth. In 2007. the European Union approved financing to develop a competing system, named Galileo.

China had some limited participation in developing Galileo, but in 2006 announced development of a GPS system of its own, to be named Beidou. Beidou is a Chinese name for the Big Dipper.