Cycles of the Sun

Length of Days & Nights

Seasons

Length of Days & Nights

• The Earth rotates on its axis

• A complete rotation takes a little over 24 hours (1 day)

• One side of the Earth is always facing the Sun

Length of Days & Nights

• The side of the Earth facing the Sun has day

• The side of the earth facing away from the Sun has night

As the Earth Rotates…

• The side of the Earth in the sunlight spins away and becomes night

• The side of the Earth in the dark spins toward the Sun and becomes day

Changing Length of Day & Day

• The number of hours of daylight received each day depends on the latitude.

• The equator receives about 12 hours of daylight all year long

Changing Length of Day & Day

• The hemisphere that is tilted toward the Sun gets more hours of daylight that the hemisphere tilted away from the Sun

• Latitudes closest to the equator have less change in hours of daylight

• Latitudes further from the equator have more dramatic changes in hours of daylight

Seasons

• The Earth is tilted on its axis

Seasons

• The tilt does not change – it always remains pointed in the same direction

Seasons

• As the Earth revolves around the Sun, the tilt sometimes points toward the Sun, sometimes away from the Sun, and sometimes neither away nor toward the Sun

Seasons

• The hemisphere that is tilted toward the Sun has summer– Longer days (more hours of sunlight)– Warmer weather

Seasons

• The hemisphere that is tilted away from the Sun has winter– Shorter days (less hours of sunlight)– Cooler weather

Seasons

• When the Earth is positioned so that the tilt is neither towards nor away from the Sun, we have Spring and Fall– Moderate temperatures– Days and nights of similar length

Seasons: Summer(Northern Hemisphere)

• Position of the Earth is such that the northern hemisphere is tilted toward the Sun

• Summer Solstice (1st day of summer)– Sun at highest point (over Tropic of

Cancer)– Most hours of sunlight (longest day)– About June 21

Seasons: Fall(Northern Hemisphere)

• Position of the Earth is such that the northern hemisphere is tilted neither towards nor away from the Sun

• Autumnal Equinox (1st day of fall)– About 12 hours of sunlight– About September 22

Seasons: Winter(Northern Hemisphere)

• Position of the Earth is such that the northern hemisphere is tilted away from the Sun

• Winter Solstice (1st day of winter)– Sun at lowest point (over Tropic of Capricorn)– Fewest hours of sunlight (shortest day)– About December 21

Seasons: Spring(Northern Hemisphere)

• Position of the Earth is such that the northern hemisphere is tilted neither towards nor away from the Sun

• Vernal Equinox (1st day of spring)– About 12 hours of sunlight– About March 21

Energy from the Sun(Insolation)

Summing Up:Summing Up:

Winter - Earth tilted away from Sun, fewer hours of sunlight, less direct sunlight (insolation)

Spring – Earth neither tilted away nor toward the Sun, equal hours of daylight and night

Summer – Earth tilted toward the Sun, more hours of daylight, more direct sunlight (insolation)

Fall - Spring – Earth neither tilted away nor toward the Sun, equal hours of daylight and night

Watch this animation:Watch this animation:

http://www.shsu.edu/%7Echm_tgc/sounds/flhttp://www.shsu.edu/%7Echm_tgc/sounds/flashfiles/earth.swfashfiles/earth.swf

Works Cited• http://www.wrh.noaa.gov/hnx/newslet/spring03/dryjanuaries.htm• http://www.nasa.gov/worldbook/wbkids/k_dayandnight.html • http://www.lpi.usra.edu/education/skytellers/day_night/activities/cycle_o

f_light.shtml• http://www.nps.gov/lacl/graphics/sun_earth2.jpg • http://www.learner.org/jnorth/images/imageshtml/earth-tilt.gif • http://costa-rica-guide.com/travel/index.php?

option=com_content&task=view&id=365&Itemid=604&limit=1&limitstart=4

• http://www.windows.ucar.edu/tour/link=/earth/climate/cli_seasons.html • http://www.worldbook.com/features/seasons/assets/tilt4.gif • http://www.springboardmagazine.com/SpringImages/seasons.gif• http://www.nmm.ac.uk/upload/img/latitude.gif• http://www.astro.virginia.edu/class/oconnell/astr121/im/hours-of-

daylight-v-date.jpg • http://en.wikipedia.org/wiki/Summer_Solstice