Download - The Seasons
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The Seasons
• Seasonality: the variation of the sun’s position over the horizon; the changing daylength during the year
• Seasons result from: variations in the sun’s altitude, the suns’s declination, and daylength, WHICH are dependent upon……
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Reasons for Seasons
• Revolution– Earth revolves around the Sun– Voyage takes one year, roughly– Earth’s speed is 107,280 kmph (66,660 mph)
• Rotation– Earth rotates on its axis once every 24 hours– Rotational velocity at equator is 1674 kmph (1041
mph)
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Reasons for Seasons
• Tilt of Earth’s axis– Axis is tilted 23.5° from plane of ecliptic
• Axial parallelism– Axis maintains alignment during orbit around the
Sun– North pole points toward the North Star (Polaris)
• Sphericity
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The Earth’s tilt and orientation hold steady as it orbits the Sun.
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Sun conditions at the Solstices and Equinoxes
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Sun’s Arc
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The Sun as seen from 45°N in June and in December.
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Seasonal Observations
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Seasonal Observations
SUMMER HEMISPHERE
Carrollton = 33°
What is Sun’s angle (at noon) on June 21?
90 – |(latitude – subsolar point)|
90 – |(33 – 23.5)| = 80.5 °
WINTER HEMISPHERE
90 – (latitude + subsolar point)
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Annual March of the Seasons
• Winter solstice – December 21 or 22– Subsolar point Tropic of Capricorn
• Spring equinox – March 20 or 21– Subsolar point Equator
• Summer solstice – June 20 or 21– Subsolar point Tropic of Cancer
• Fall equinox – September 22 or 23– Subsolar point Equator