Cycles of the Sun

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Cycles of the Sun

• Length of Days Nights
• Seasons

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Length of Days Nights

• The Earth rotates on its axis
• A complete rotation takes about 24 hours (1 day)
• One side of the Earth is always facing the Sun

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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

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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

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Changing Length of Day Night

• The number of hours of daylight received each day
  depends on the latitude.
• The equator receives about 12 hours of daylight
  all year long

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Changing Length of Day Day

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

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Seasons

• The Earth is tilted on its axis

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Seasons

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

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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

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Seasons

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

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Seasons

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

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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

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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

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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

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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

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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

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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
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Works Cited

• http//www.wrh.noaa.gov/hnx/newslet/spring03/dryja
  nuaries.htm
• http//www.nasa.gov/worldbook/wbkids/k_dayandnight
  .html
• http//www.lpi.usra.edu/education/skytellers/day_n
  ight/activities/cycle_of_light.shtml
• http//www.nps.gov/lacl/graphics/sun_earth2.jpg
• http//www.learner.org/jnorth/images/imageshtml/ea
  rth-tilt.gif
• http//costa-rica-guide.com/travel/index.php?optio
  ncom_contenttaskviewid365Itemid604limit1
  limitstart4
• http//www.windows.ucar.edu/tour/link/earth/clima
  te/cli_seasons.html
• http//www.worldbook.com/features/seasons/assets/t
  ilt4.gif
• http//www.springboardmagazine.com/SpringImages/se
  asons.gif
• http//www.nmm.ac.uk/upload/img/latitude.gif
• http//www.astro.virginia.edu/class/oconnell/astr1
  21/im/hours-of-daylight-v-date.jpg
• http//en.wikipedia.org/wiki/Summer_Solstice