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Seasons on Earth. All Figures from http://www.fourmilab.ch/earthview/vplanet.html. By Diana L. Duckworth Rustburg High School Campbell County, VA. Three Factors Cause Seasons. Tilt of Earth at 23.5 degrees latitude Greater tilt - more extreme seasons Less tilt - less extreme seasons
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Seasons on Earth All Figures from http://www.fourmilab.ch/earthview/vplanet.html By Diana L. Duckworth Rustburg High School Campbell County, VA
Three Factors Cause Seasons • Tilt of Earth at 23.5 degrees latitude • Greater tilt - more extreme seasons • Less tilt - less extreme seasons • Revolution of Earth around Sun • Elliptical orbit • Perihelion - January • Aphelion - July • Parallelism of Axis of Rotation • Axis always points toward Polaris
Tilt of Axis • Causes sun to be directly overhead at a different latitude each day • Summer Solstice @ 23.5N (~June 21) • More daylight & more intense radiation in Northern Hemisphere • Winter Solstice @ 23.5S (~December 21) • More daylight and more intense radiation in Southern Hemisphere • Equinox (twice a year) @ Equator • Days & Nights are 12 hours each everywhere
Key to Figures • In the following illustrations, the dark area represents the 50% of the earth that is in darkness and the light areas represent the 50% of the earth that is in daylight. • In all figures, the sun can be considered to be in the geographic center of the image.
Tilt of Axis Locates Key Latitudes • Tropic of Cancer - where Sun’s rays are vertical at Summer Solstice = tilt 23.5N • Tropic of Capricorn - where Sun’s rays are vertical at Winter Solsltice = tilt 23.5S • Arctic Circle - latitude of total daylight at Summer Solstice or darkness at Winter Solstice • 90 - tilt = 90N - 23.5N = 66.5N • Antarctic Circle - latitude of total daylight at Winter Solstice or darkness at Summer Solstice • 90 - tilt = 90S - 23.5S = 66.5S
As the World Turns Rotation has nothing to do with seasons!
Changes with the Seasons • Maximum elevation of sun & position in sky from Northern Hemisphere • June to December - gets lower & farther to South • December to June - gets higher & farther to North • Length of Daylight • June to December - daylight gets shorter • December to June - daylight gets longer