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Why We Have Seasons:

• Seasons are caused by the 23.5 0 tilt of Earth combined with Earth’s revolution around the Sun

• Earth’s axis is always pointed in the same direction (fixed position)

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Tropic of Cancer

Equator

Equator

Tropic of Capricorn~9hrs

~12 hrs

~15hrs

~12 hrs

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24 hrs daylight

24 hrs daylight

24 hrs darkness

24 hrs darkness

Why is there More Hrs of Daylight in Summer?

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Summer Solstice• 1st day of Summer• June 20th or 21st (N.H.)• Day of the year with the most hrs of daylight

(~15)• Sunlight is hitting Tropic of Cancer

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Autumnal Equinox

• 1st day of Fall• Sept 22nd or 23rd (N.H.)• Day of the year with

about equal hrs of daylight (~12)

• Sunlight is hitting Equator

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Winter Solstice

•1st day of Winter•Dec 21st or 22nd (N.H.)•Day of the year with the least hrs of daylight (~9)•Sunlight is hitting Tropic of Capricorn

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Vernal Equinox• 1st day of Spring• march 20th or 21st (N.H.)• Day of the year with about equal hrs of daylight

(~12)• Sunlight is hitting Equator

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Summer Solstice (15 hrs daylight)

Winter Solstice (9 hrs daylight)

Fall Equinox (12 hrs daylight)

Vernal Equinox (12 hrs daylight)

Summer Solstice (15 hrs daylight)

Hrs of daylight decrease

Hrs of daylight increase

Hrs of daylight increase

Hrs of daylight decrease

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Seasons Animations:

• http://projects.astro.illinois.edu/data/Seasons/seasons.html

• http://esminfo.prenhall.com/science/geoanimations/animations/01_EarthSun_E2.html

• http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.html

Video clipVideo clip #2

Bill Nye Seasons