Editing Solar zenith angle (section)

==Applications==

===Sunrise/Sunset===
{{Main articles|Sunrise equation}}
Sunset and sunrise occur (approximately) when the zenith angle is 90°, where the hour angle ''h''<sub>0</sub> satisfies<ref name="hartmann" />
<math display="block">\cos h_0 = -\tan \Phi \tan \delta.</math>

Precise times of sunset and [[Sunrise#Angle|sunrise]] occur when the upper limb of the Sun appears, as refracted by the atmosphere, to be on the horizon.

===Albedo===
A weighted daily average zenith angle, used in computing the local [[albedo of the Earth]], is given by
<math display="block">\overline{\cos \theta_s} = \frac{\displaystyle \int_{-h_0}^{h_0} Q \cos \theta_s \, \text{d}h}{\displaystyle \int_{-h_0}^{h_0} Q \, \text{d}h}</math>
where ''Q'' is the instantaneous [[irradiance]].<ref name="hartmann" />

===Summary of special angles===
{{Subsolar point date graph|300px|float=right}}
For example, the solar elevation angle is:
* 90° at the [[subsolar point]], which occurs, for example, at the equator on a day of equinox at solar noon
* near 0° at the sunset or at the sunrise
* between −90° and 0° during the night (midnight)

An exact calculation is given in [[position of the Sun]]. Other approximations exist elsewhere.<ref>{{cite web|last=livioflores-ga|url=http://answers.google.com/answers/threadview/id/782886.html|title=Equation to know where the Sun is at a given place at a given date-time|accessdate=9 March 2013}}</ref>