Presentation on theme: "Seasons on Earth All Figures from planet.html By Diana L. Duckworth Rustburg High School Campbell County, VA."— Presentation transcript:
Seasons on Earth All Figures from http://www.fourmilab.ch/earthview/v planet.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
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