History Meme: 3/3 Inventions
A sextant is an instrument used to measure the angle between any two visible objects. Its primary use is to determine the angle between a celestial object and the horizon which is known as the object’s altitude. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. Common uses of the sextant include sighting the sun at solar noon and sighting Polaris at night (in the Northern Hemisphere), to find one’s latitude. A sextant can also be used to measure the lunar distance between the moon and another celestial object in order to determine Greenwich time which is important because it can then be used to determine the longitude.
Sir Isaac Newton invented the principle of the doubly reflecting navigation instrument, but never published it. Two men independently developed the octant around 1730: John Hadley, an English mathematician, and Thomas Godfrey, a glazier in Philadelphia. John Bird made the first sextant in 1757. The octant and later the sextant, replaced the Davis quadrant as the main instrument for navigation.