View source for Astronomy:Effect of Sun angle on climate

The amount of [[Physics:Heat|heat]] energy received at any location on the globe is a direct '''effect of Sun angle on climate''', as the [[Physics:Angle of incidence (optics)|angle]] at which [[Astronomy:Sunlight|sunlight]] strikes [[Astronomy:Earth|Earth]] varies by location, time of day, and [[Physics:Season|season]] due to [[Astronomy:Earth's orbit|Earth's orbit]] around the [[Astronomy:Sun|Sun]] and [[Earth's rotation]] around its [[Astronomy:Axial tilt|tilted axis]]. Seasonal change in the angle of sunlight, caused by the tilt of Earth's [[Rotation around a fixed axis|axis]], is the basic mechanism that results in warmer weather in summer than in winter.<ref>Windows to the Universe. [http://www.windows.ucar.edu/tour/link=/earth/climate/cli_seasons.html Earth's Tilt Is the Reason for the Seasons!] {{Webarchive|url=https://web.archive.org/web/20070808022809/http://www.windows.ucar.edu/tour/link=/earth/climate/cli_seasons.html |date=2007-08-08 }} Retrieved on 2008-06-28.</ref><ref name="SunModel">{{Cite journal|url=http://sites.google.com/site/khavrus/public-activities/SolarEng|last1=Khavrus|first1=V.|title=Introduction to solar motion geometry on the basis of a simple model|year=2010|journal=Physics Education|volume=45|doi=10.1088/0031-9120/45/6/010|page=641|last2=Shelevytsky|first2=I.|issue=6|bibcode=2010PhyEd..45..641K|s2cid=120966256 |access-date=2011-05-13|archive-date=2016-09-16|archive-url=https://web.archive.org/web/20160916180315/https://sites.google.com/site/khavrus/public-activities/SolarEng|url-status=dead}}</ref><ref name="SunModel2">{{Cite journal|url=http://sites.google.com/site/khavrus/public-activities/seasons|last1=Khavrus|first1=V.|title=Geometry and the physics of seasons|year=2012|journal=Physics Education|volume=47|doi=10.1088/0031-9120/47/6/680|page=680|last2=Shelevytsky|first2=I.|issue=6 |s2cid=121230141 }}</ref> Change in [[Astronomy:Daytime|day length]] is another factor.<ref name="SunModel" /><ref name="SunModel2" />
== Geometry of Sun angle ==
[[Image:oblique rays 04 Pengo.svg|thumb|400px|right|'''Figure 1'''<br>This diagram illustrates how sunlight is spread over a greater area in the polar regions. In addition to the density of incident light, the [[Dissipation|dissipation]] of light in the atmosphere is greater when it falls at a shallow angle.]]
[[Image:seasons.too.png|thumb|400px|right|'''Figure 2'''<br>One sunbeam one mile wide shines on the ground at a 90° angle, and another at a 30° angle. The one at a shallower angle covers twice as much area with the same amount of light energy.]]

'''Figure 1''' presents a case when sunlight shines on Earth at a lower [[Physics:Angle of incidence (optics)|angle]] (Sun closer to the horizon), the energy of the sunlight is spread over a larger area, and is therefore weaker than if the Sun is higher overhead and the energy is concentrated on a smaller area.

'''Figure 2''' depicts a sunbeam {{convert|1|mi|spell=in}} wide falling on the ground from directly overhead, and another hitting the ground at a 30° angle.  [[Trigonometry]] tells us that the [[Sine|sine]] of a 30° angle is 1/2, whereas the sine of a 90° angle is 1.  Therefore, the sunbeam hitting the ground at a 30° angle spreads the same amount of light over twice as much area (if we imagine the Sun shining from the south at [[Astronomy:Noon|noon]], the north–south width doubles; the east–west width does not). Consequently, the amount of light falling on each square mile is only half as much.

[[Image:seasons.svg|right|250px|thumb|'''Figure 3'''<br/>This is a diagram of the seasons.  Regardless of the time of day (i.e. Earth's rotation on its axis), the North Pole will be dark, and the South Pole will be illuminated; see also arctic winter.]]

'''Figure 3''' shows the angle of sunlight striking Earth in the [[Earth:Northern Hemisphere|Northern]] and [[Earth:Southern Hemisphere|Southern]] Hemispheres when Earth's northern axis is tilted away from the Sun, when it is winter in the north and summer in the south.

===Technical note===
[[Physics:Thermal radiation|Heat energy]] is not received from the Sun. Rather, [[Astronomy:Solar irradiance|radiant energy]] is received and this results in change in [[Physics:Thermal energy|energy level]] of receiving bodies in Earth's domain. Different materials have different properties for transmitting back received energy in the form of ''heat energy'' at different rates.

==See also==
* [[Astronomy:Axial tilt|Axial tilt]]
* [[Declination]]
* [[Astronomy:Solar irradiance|Solar irradiance]] (insolation)
* [[Astronomy:Sun path|Sun path]]

==References==
{{reflist}}

[[Category:Climate variability and change]]
[[Category:Atmospheric radiation]]

{{Sourceattribution|Effect of Sun angle on climate}}