Navigators could determine their latitude by measuring the sun's angle at noon (i.e., when it reached its highest point in the sky, or culmination) or, in the Northern Hemisphere, to measure the angle of Polaris (the North Star) from the horizon (usually during twilight).

Until the mid-1750s, accurate navigation at sea out of sight of land was an unsolved problem due to the difficulty in calculating longitude. Altitude considerations can naturally be ignored for vessels operating at sea level. To determine a position on the Earth's surface, it is necessary and sufficient to know the latitude, longitude, and altitude. History The marine 'Chronometer' of Jeremy Thacker used gimbals and a vacuum in a bell jar.įurther information: History of longitude It has recently become more commonly used to describe watches tested and certified to meet certain precision standards.

The term chronometer was coined from the Greek words χρόνος ( chronos) (meaning time) and meter (meaning measure) in 1713 by the English cleric and scientist William Derham. The first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval (and later aerial) navigation. When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage was vital for effective navigation, lacking electronic or communications aids. It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at the current location found from observations of celestial bodies. Chronometer circa 1844-1860.Ī marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. A marine chronometer by Charles Frodsham of London, shown turned upside down to reveal the movement.

Cronometer app