Dictionary:Obliquity factor

(∂ blik’ wi tē) A factor derived by Stokes for use with Huygens’ principle to show that the major energy in a wave moves forward and to prevent backward propagation:

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): {\displaystyle cos{\frac{\phi}{2}} \approx \frac{1+cos{\phi}}{2} } ,

where Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://en.wikipedia.org/api/rest_v1/":): \phi is the angle between the directions of reradiation and of approach.