Editing Solar azimuth angle (section)

==Conventional sign and origin==
There are several conventions for the solar azimuth; however, it is traditionally defined as the angle between a line due [[south]] and the shadow cast by a vertical rod on [[Earth]]. This convention states the angle is positive if the shadow is [[east]] of south and negative if it is [[west]] of south.<ref name="sukhatme">{{cite book |title=Solar Energy: Principles of Thermal Collection and Storage |first=S. P. |last=Sukhatme |date=2008 |edition=3rd |publisher=Tata McGraw-Hill Education |isbn=978-0070260641 |page=84}}</ref><ref name="Seinfeld and Pandis">{{cite book |title=Atmospheric Chemistry and Physics, from Air Pollution to Climate Change |first1=John H. |last1=Seinfeld |first2=Spyros N. |last2=Pandis |date=2006 |edition=2nd |publisher=Wiley |isbn=978-0-471-72018-8 |page=130 |url=http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471720186.html |access-date=2013-05-01 |archive-date=2013-09-06 |archive-url=https://web.archive.org/web/20130906094320/http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471720186.html |url-status=dead }}</ref> For example, due east would be 90° and due west would be -90°. Another convention is the reverse; it also has the origin at due south, but measures angles clockwise, so that due east is now negative and west now positive.<ref name="Duffie">{{cite book |title=Solar Engineering of Thermal Processes |first1=John A. |last1=Duffie |first2=William A. |last2=Beckman |date=2013 |edition=4th |publisher=Wiley |isbn=978-0-470-87366-3 |pages=13, 15, 20 |url=http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470873663.html}}</ref>

However, despite tradition, the most commonly accepted convention for analyzing [[solar irradiation]], e.g. for [[solar energy]] applications, is clockwise from due [[north]], so east is 90°, south is 180°, and west is 270°. This is the definition used by [[National Renewable Energy Laboratory|NREL]] in their solar position calculators<ref name="SPA">{{cite journal |last=Reda, I. |first=Andreas, A. |title=Solar Position Algorithm for Solar Radiation Applications |journal=Solar Energy |volume=76 |issue=5 |date=2004 |pages=577–89 |doi=10.1016/j.solener.2003.12.003 |issn=0038-092X |bibcode=2004SoEn...76..577R}}</ref> and is also the convention used in the [[#Formulas|formulas]] presented here. However, [[Landsat]] photos and other [[United States Geological Survey|USGS]] products, while also defining azimuthal angles relative to due north, take counter[[clockwise]] angles as negative.<ref>{{cite web |url=https://lta.cr.usgs.gov/landsat_dictionary.html#sun_azimuth |title=Sun Azimuth |work=Landsat Data Dictionary |publisher=[[United States Geological Survey|USGS]]}}</ref>