Arcsecond | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-10-03

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Minute_and_second_of_arc


00:02:36 1 Symbols and abbreviations
00:03:57 2 Common examples
00:05:45 3 Uses
00:05:54 3.1 Astronomy
00:08:24 3.2 Cartography
00:09:55 3.3 Property cadastral surveying
00:11:04 3.4 Firearms
00:12:54 3.5 Human vision
00:13:16 3.6 Materials
00:13:39 3.7 Manufacturing
00:19:50 4 See also
00:20:12 5 Notes
00:20:41 6 References
00:21:08 7 External links



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SUMMARY
=======
A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn (or complete rotation), one minute of arc is 1/21600 of a turn.  The nautical mile was originally defined as a minute of latitude on a hypothetical spherical Earth so the actual Earth circumference is very near 21 600 nautical miles.  A minute of arc is π/10800 of a radian.
A second of arc, arcsecond (arcsec), or arc second is 1/60 of an arcminute, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 (about 1/206265) of a radian.
These units originated in Babylonian astronomy as sexagesimal subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy, optometry, ophthalmology, optics, navigation, land surveying, and marksmanship.
To express even smaller angles, standard SI prefixes can be employed; the milliarcsecond (mas) and microarcsecond (μas), for instance, are commonly used in astronomy.
The number of square arcminutes in a complete sphere is 
  
    
      
        4
        π
        
          
            (
            
              
                
                  10
                  
                  800
                
                π
              
            
            )
          
          
            2
          
        
        =
        
          
            
              466
              
              560
              
              000
            
            π
          
        
        ≈
      
    
    {\displaystyle 4\pi \left({\frac {10\,800}{\pi }}\right)^{2}={\frac {466\,560\,000}{\pi }}\approx }
   148510660 square arcminutes (the surface area of a unit sphere in square units divided by the solid angle area subtended by a square arcminute, also in square units – so that the final result is a dimensionless number).
The names "minute" and "second" have nothing to do with the identically named units of time "minute" or "second". The identical names reflect the ancient Babylonian number system, based on the number 60.