The Seasons - the rays of the Sun strike the ground more...

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The Seasons There is a popular misconception that the seasons on the Earth are caused by varying distances of the Earth from the Sun on its elliptical orbit. This is not correct. One way to see that this reasoning may be in error is to note that the seasons are out of phase in the Northern and Southern hemispheres: when it is Summer in the North it is Winter in the South. Seasons in the Northern Hemisphere The primary cause of the seasons is the 23.5 degree of the Earth's rotation axis with respect to the plane of the ecliptic, as illustrated in the adjacent image ( Source ). This means that as the Earth goes around its orbit the Northern hemisphere is at various times oriented more toward and more away from the Sun, and likewise for the Southern hemisphere, as illustrated in the following figure. The Seasons in the Northern Hemisphere Thus, we experience Summer in the Northern Hemisphere when the Earth is on that part of its orbit where the N. Hemisphere is oriented more toward the Sun and therefore the Sun rises higher in the sky and is above the horizon longer, and
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Unformatted text preview: the rays of the Sun strike the ground more directly. Likewise, in the N. Hemisphere Winter the hemisphere is oriented away from the Sun, the Sun only rises low in the sky, is above the horizon for a shorter period, and the rays of the Sun strike the ground more obliquely. In fact, as the diagram indicates, the Earth is actually closer to the Sun in the N. Hemisphere Winter than in the Summer (as usual, we greatly exaggerate the eccentricity of the elliptical orbit in this diagram). The Earth is at its closest approach to the Sun (perihelion) on about January 4 of each year, which is the dead of the N. Hemisphere Winter. (The time for perihelion, aphelion, and the solstices for any year 1992-2000 is available in this compilation .) For a more extensive introduction to how variations in the amount of solar energy reaching the Earth's surface influence climate, see this discussion of solar databases for global change models....
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This note was uploaded on 12/04/2011 for the course ANT ANT2000 taught by Professor Monicaoyola during the Fall '10 term at Broward College.

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The Seasons - the rays of the Sun strike the ground more...

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