Effect of sun angle on climate
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2008-06-28T13:53:09Z
Thegreatdr
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Wikifying lead by bolding the title and inserting it into the first line
[[Image:Oblique rays 04 Pengo.svg|right|250px|thumb|'''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]] of light in the [[Earth's atmosphere|atmosphere]] is greater when it falls at a shallow angle.]]
[[Image:seasons.svg|right|250px|thumb|'''Figure 3'''<br/>This is a diagram of the seasons. Regardless of the time of day (i.e. the [[Earth]]'s rotation on its axis), the [[North Pole]] will be dark, and the [[South Pole]] will be illuminated; see also [[arctic winter]].]]
The amount of heat energy received at any location on the globe is a direct '''effect of sun angle of climate''', as the [[Angle of incidence|angle]] at which [[sunlight]] strikes the earth varies by location, time of day, and [[season]] due to the earth's orbit around the sun and the earth's revolution around its tilted axis. Seasonal change in the angle of sunlight, caused by the tilt of the earth's [[axis of rotation|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!] Retrieved on [[2008-06-28]].</ref> Change in [[day length]] is another factor. (See also [[season]].)
== Geometry of sun angle ==
[[Image:seasons.too.png|thumb|none|400px|left|'''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.]]
When sunlight shines on the earth at a lower [[Angle of incidence|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. (See Figure 2.)
'''Figure 1''' shows the angle of sunlight striking the earth in the [[Northern hemisphere|Northern]] and [[equator]] when the earth's northern axis is tilted away from the sun.
'''Figure 2''' depicts a sunbeam one mile wide falling on the ground from directly overhead, and another hitting the ground at a 30° angle. [[Trigonometry]] tells us that the [[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 [[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.
The sunbeam entering at the shallower angle must also travel twice as far through the Earth's [[atmosphere]], which reflects some of the energy back into space.
===Technical note===
[[Thermal radiation|Heat energy]] is not received from the Sun. [[Solar radiation|Radiant energy]] is received and this results in change in [[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. [[Concrete]] and [[tar]] for example are slow releasers. Most [[metals]] are fast releasers.
==See also==
* [[Axial tilt]]
* [[Declination]]
==References==
{{reflist}}
[[Category:Climate]]
[[Category:Seasons]]
[[Category:Atmospheric radiation]]
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