Editing Hour angle (section)

==Solar hour angle{{anchor|Solar}}==
{{see also|Sunrise equation}}

Observing the Sun from Earth, the ''solar hour angle'' is an expression of time, expressed in angular measurement, usually degrees, from [[solar noon]]. At solar noon the hour angle is zero degrees, with the time before solar noon expressed as negative degrees, and the local time after solar noon expressed as positive degrees. For example, at 10:30 AM local apparent time the hour angle is −22.5° (15° per hour times 1.5 hours before noon).<ref>{{Cite book | last1 = Kreider | first1 = J. F. | chapter = Solar Energy Applications | doi = 10.1002/9780470209738.ch2 | title = Environmentally Conscious Alternative Energy Production | pages = 13–92 | year = 2007 | isbn = 9780470209738 }}</ref>

The [[cosine]] of the hour angle (cos(''h'')) is used to calculate the [[solar zenith angle]]. At solar noon, {{math|1=''h'' = 0.000}} so {{math|1=cos(''h'') = 1}}, and before and after solar noon the cos(±&nbsp;''h'') term = the same value for morning (negative hour angle) or afternoon (positive hour angle), so that the Sun is at the same altitude in the sky at 11:00AM and 1:00PM solar time.<ref>{{Cite book | last1 = Schowengerdt | first1 = R. A. | chapter = Optical radiation models | doi = 10.1016/B978-012369407-2/50005-X | title = Remote Sensing | pages = 45–88 | year = 2007 | isbn = 9780123694072 }}</ref>