John Hadley

John Hadley (April 16, 1682 – February 14, 1744) invented the sextant around 1730. The sextant allows its user to determine the elevation of celestial objects with respect to the horizon. If the position of the object on the sky and the time of the observation are known, it is easy for the user to calculate his latitude. The sextant proved extremely valuable for navigation and displaced the use of the astrolabe.

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An American, Thomas Godfrey, independently invented the sextant at approximately the same time.

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Hadley also improved the reflector telescope, building the first Newtonian telescope in 1721.

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Mons Hadley and Rima Hadley on the Moon are named after him.

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February 14: February 14 is the 45th day of the year in the Gregorian Calendar. There are 320 days remaining, 321 in leap years....

Sextant: A sextant is a measuring instrument used to measure the angle of elevation of a celestial object above the horizon. Making this measurement is known as sighting the object or taking a sight. The angle, and the time when it was measured, are used to calculate a position line on a nautical or aerona...

Celestial: The term celestial refers to the sky and/or Heaven. An astronomical object is sometimes referred to as a celestial body or celestial object....

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