Flattening

Flattening is a measure of the compression of a <a href="/facts/Circle/9fy5ggKn">circle</a> or <a href="/facts/Sphere/jywYLNM2">sphere</a> along a diameter to form an <a href="/facts/Ellipse/1wUDnGxY">ellipse</a> or an <a href="/facts/Ellipsoid/pe9vm0Sh">ellipsoid</a> of revolution (<a href="/facts/Spheroid/GJyyLxQ7">spheroid</a>) respectively. Other terms used are ellipticity, or oblateness. The usual notation for flattening is 
 
 
 
 f
 
 
 {\displaystyle f}
 
 and its definition in terms of the <a href="/facts/Semi-major_and_semi-minor_axes/l7JES2wo">semi-axes</a> 
 
 
 
 a
 
 
 {\displaystyle a}
 
 and 
 
 
 
 b
 
 
 {\displaystyle b}
 
 of the resulting ellipse or ellipsoid is

f
        =
        
          
            
              a
              −
              b
            
            a
          
        
        .
      
    
    {\displaystyle f={\frac {a-b}{a}}.}

The compression factor is 
 
 
 
 b
 
 /
 
 a
 
 
 {\displaystyle b/a}
 
 in each case; for the ellipse, this is also its <a href="/facts/Aspect_ratio/1LVBgtfT">aspect ratio</a>.

Flattening open-in-new

Flattening