**Navigation is finding one’s way at sea and in the air.** Without roads, the navigator relies on coastal, celestial and electronic marks. The word navigate comes from the Latin words for ship *(navis)* and “to drive or guide”* (agere).*

Navigation is both art and science and requires understanding of the earth and heavens. Changes in navigation science and technology over the last five hundred years have altered the navigator’s work and methods. Yet, the navigator’s basic task remains constant: to keep track of where the ship has been and where it is now, and to plan where the ship will go next.

Navigation is based on astronomy, physics, oceanography, meteorology, earth sciences, aerodynamics, and hydrodynamics. Mathematics can include arithmetic, algebra, trigonometry, logarithms, geometry, and analysis. The navigator needs practical judgment to make good decisions with incomplete or overly complex data.

While today’s electronics have helped automate navigation, they also provide much more information for the navigator to process, and the navigator has to be prepared for electronic failure. The work of navigation requires care, but it is fascinating in that it combines so many disciplines, and requires forethought and planning.

**Early Astronomers**

**Ptolemy, Claudius**

**c.90-168.** Probably born in Egypt of Greek heritage. Mathematician, astronomer and cartographer. With simple projections he created a world map that summarized geographic information of the Greco-Roman world. He created a latitude/longitude system to describe locations. He conceived a world or heliocentric model of the Universe to explain celestial motions, drawing on the work of Greek and Babylonian astronomers. Both of these served for practical navigation until the 15th century.

**Copernicus, Nicholas**

**1473-1543.** Polish astronomer and mathematician who developed and published the view of an earth that orbited a stationary sun. His book *De revolutionibus orbium coelestium* (On the Revolutions of the Celestial Spheres) was printed just before his death.

**Kepler, Johannes**

**1571-1630.** German astronomer and mathematician who theorized that planets and the Earth travel around the sun in elliptical orbits. He published his theory in 1609. Using his theory, he was able to calculate precise predictive tables for planetary motion.

**Galilei, Galileo**

**1564-1642.** Italian mathematician, astronomer and instrument maker. In 1609, basing his work on a description of a Dutch telescope, he developed the first practical telescope which he used to discover the moons of Jupiter the following year. This tool was an astronomical breakthrough, for no longer were astronomers dependent on their eyes alone for observation.

**Newton, Sir Isaac**

1643- 1727. English mathematician who laid the groundwork for calculus and did breakthrough work in optics and gravitation. In 1687, he published his Principia Mathematica in which he applied his laws of motion to the motion of celestial bodies, providing the mathematics to prove Kepler’s theories. These would be used by future astronomers to produce navigational tables. He also developed the universal law of gravitation.

**Aristotle**

He is sometimes called the grandfather of science. He studied under the great philosopher Plato and later started his own school, the Lyceum at Athens. He, too, believed in a geocentric Universe and that the planets and stars were perfect spheres though Earth itself was not. He further thought that the movements of the planets and stars must be circular since they were perfect and if the motions were circular, then they could go on forever. Today, we know that none of this is the case, but Aristotle was so respected that these wrong answers were taught for a very long time. Aristotle, outside of astronomy, was a champion observer. He was one of the first to study plants, animals, and people in a scientific way, and he did believe in experimenting whenever possible and developed logical ways of thinking. This is a critical legacy for all the scientists who followed after him.

Source: penobscotmarinemuseum.org