John Hadley
John Hadley
1682-1744
English mathematician and inventor who built the first working reflector telescope. Hadley built his Gregorian reflector telescope in 1721. The device contained a 6-inch (15.2-cm) mirror, and proved accurate enough to be successfully used by astronomers. The response to Hadley's invention was so favorable, he later built a larger, more sophisticated version. In 1730 he invented a quadrant, known as Hadley's quadrant, which was used to measure the altitude of the Sun or a star in order to ascertain a ship's geographic position while out at sea. His design eventually evolved into a sextant, a navigational instrument that measured the distance between the horizon and either the Sun or stars.
More From encyclopedia.com
Parallax , Astronomers must use very indirect methods to measure the distances to stars and other astronomical objects. Measuring a star's parallax is a way to… Friedrich Wilhelm Bessel , Bessel, Friedrich Wilhelm
Bessel, Friedrich Wilhelm
astronomy, geodesy, mathematics.
Bessel’s father was a civil servant in Minden; his mother was th… John Michell , MICHELL, JOHN
astronomy.
Michell earned a permanent place in the history of stellar astronomy for two signal accomplishments: he was the first to mak… Stellar Magnitudes , Of principle importance to general astronomical observation is the observable brightness of the stars. Magnitude is the unit used in astronomy to des… Astrolabe , An astrolabe is an astronomical instrument once widely used to measure stars or planets to determine latitude and time, primarily for navigational pu… Telluride , telluride •hayride • chloride • joyride • telluride •sun-dried • fluoride • saccharide
You Might Also Like
NEARBY TERMS
John Hadley