write short notes on : Astrolabe , sextant , jacob's staff and magnetic compass.
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Answer:
An astronomical instrument for taking the altitude of the sun or stars and for the solution of other problems in astronomy and navigation: used by Greek astronomers from about 200 b.c. and by Arab astronomers from the Middle Ages until superseded by the sextant.
A sextant can measure an angle on any plane, and works by a principle of double reflection.
The term Jacob's staff, also known as cross-staff, a ballastella, a fore-staff, or a balestilha, is used to refer to several things.
A compass is an instrument used for navigation and orientation that shows direction relative to the geographic cardinal directions. Usually, a diagram called a compass rose shows the directions north, south, east, and west on the compass face as abbreviated initials.