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2.1.7: Day Length and Seasons

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    Day length is determined by the length of time the Sun is above the horizon. Day length changes through the year as the orientation of the Earth to the Sun changes. The circle of illumination is the imaginary circle that separate day from night.

    Variations in day length
    Figure \(\PageIndex{1}\): Variations in day length.

    Figure \(\PageIndex{1}\) shows two extreme cases, the December and June solstices. Note during December that more of a given latitude in the Southern hemisphere is exposed to the Sun. This is the longest day of the year for those living poleward of the Equator. In June the opposite occurs with longer day length in the Northern hemisphere. Note that in both cases, the circle of illumination bisects the Equator (cuts it in half). The Equator is the only place on Earth that experiences equal day length every day of the year. The Earth's axis is neither inclined toward or away from the Sun on the equinoxes and so the circle of illumination cuts all latitudes in half resulting in equal day length for the entire Earth.

    To summarize the changing seasonal conditions:

    Table \(\PageIndex{1}\): Earth- Sun Relations and Season
     

       SPRING EQUINOX

      WINTER SOLSTICE

    AUTUMNAL EQUINOX

      SUMMER SOLSTICE

    Date

    March 21

    December 22

    Sept. 23

    June 21

    Subsolar Point

    0o 

    23 1/2S

    0o 

    23 1/2o N

    Tangent Rays

    North and South Poles

    Arctic and Antarctic Circles

    North and South Poles

    Arctic and Antarctic Circles

      Day length

    12 hour day length everywhere

    24 hours of darkness at North Pole; 24 hours day light at South Pole; 12 hours day light at Equator

    12 hour day length everywhere

    24 hours of darkness at South Pole; 24 hours day light at North Pole; 12 hours day light at  Equator


    This page titled 2.1.7: Day Length and Seasons is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Michael E. Ritter (The Physical Environment) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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