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, 15:53, October 5, 2007
mThe [[angle]] that a ray of [[sun]] makes with a line [[perpendicular]] to the surface. For example, a surface that directly faces the [[sun]] has a [[solar]] angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of [[incidence]] is 90°.<ref>http://www1.eere.energy.gov/solar/solar_glossary.html</ref>
== References ==
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