Re: Degrees or Arc minutes to Km's

From: Ed Davies (edavies@nildram.co.uk)
Date: Mon Jun 30 2003 - 07:03:47 EDT

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    Russ Bessom wrote:
    > 
    > Greetings all,
    > I know this is off topic but I didn't know what other group to pose this
    > question...What is the equivalent of Arc minutes to Km's  or Degrees to
    > Km's.  
    
    As Tony Beresford replied, the way to do this accurately is using radians.
    However, the nearly equivalent "one in 60" rule of thumb is often useful:  
    
       An object of unit width subtends one degree at a distance of 
       about 60 units.
    
    E.g., if two satellites are 1.5 apart at a range of 600km then their 
    separation perpendicular to the line of sight will be pretty close to 
    15 km.
    
    For distances on the Earth's surface and angles subtended at the centre of 
    the Earth: 1 arc minute subtends about 1 nautical mile (that's where the
    nautical mile originally came from).  An international nautical mile is 
    now 1852 metres exactly which is about 1.15 statute miles.  1 therefore 
    shows up on the surface as 60 NM, 69 statute miles or 111 km, roughly.
    
    Ed Davies.
    
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