Unit 1-3 RETEACHING SEASONS

Vocabulary to Know:

Rotation - the spinning of the Earth on its axis; one rotation takes 24 hours or 1 day

Revolution - orbit of the Earth around the sun; this takes 365 1/4days (1 year) to complete

Orbit - path that Earth makes around the Sun

Tilt - the Earth is tipped 23.5 degrees

Axis - an imaginary line that goes through both of the planet's poles. The Earth rotates around this line.

Equator - It is halfway between the North and South Pole, at 0 degrees latitude. Divides Earth into Northern and Southern Hemisphere. We live in the Northern Hemisphere of Earth.

Summer solstice - Approximately June 22 in the Northern Hemisphere the

  • Sun is highest in the sky
  • Directly overhead at latitude 23.5º N, the Tropic of Cancer.
  • The Earth's axis is tilted mosttowardsthe sun
  • The longest day (most hours of daylight
  • The beginning of summer

Autumnal Equinox - Approximately September 23 in the Northern Hemisphere

  • Sun passes directly over the equator
  • The Earth's axis is neither tilted toward nor away from the Sun
  • The day is the same length (12 hours ) everywhere
  • The beginning of fall

Winter Solstice - Approximately December 22 in the Northern Hemisphere

  • Sun is lowest in the sky
  • Directly overhead at latitude 23.5ºS, the Tropic of Capricorn
  • The Earth's axis is tilted mostawayfrom the sun
  • The shortest day (fewest hours of daylight)
  • The beginning of winter

Vernal Equinox - Approximately March 20 in the Northern Hemisphere

  • Sun passes directly over the equator
  • The Earth's axis is neither tilted toward nor away from the Sun
  • The day is the same length (12 hours ) everywhere
  • The beginning of spring

Seasons are caused by the tilt of the Earth's axis

  • The Earth rotates around the axis every day (24 hours)Axis is tipped 23.5 degrees
  • In summer, the northern hemisphere is tipped toward the sun.
  • The sun's rays beat down upon the earth from almost straight overhead.
  • Direct rays or direct energy from the Sun (focused sunlight)
  • North Pole has constant daylight
  • In winter, the northern hemisphere is tipped away from the sun
  • The sun's rays beat down upon the earth from an angle (slanted)
  • Indirect rays or energy from the Sun (scattered sunlight over a larger area)
  • North Pole has constant night

The tilt of the earth's axis causes the number of daylight

hours to vary during the year

  • Longer days - more hours of sunlight in the summer
  • Shorter days - less hours of sunlight in the winter

As the Earth revolves around the Sun, the part of the earth

that is tilted toward the Sun changes

The angle of the tilt does not change

In Summer, the northern hemisphere is pointed toward the Sun, and the sun's rays are more direct and concentrated (more sunlight energy)

On June 21, the summer solstice, the top of the axis is tilted directly toward the sun. Areas north of the equator (the northern hemisphere) have longer days and shorter nights.

In Winter, the northern hemisphere tilts away from the Sun. It spends more time in darkness (has longer nights) and the sun's rays are not as direct (less sunlight energy).

On December 21, the winter solstice, the top of earth's axis is tilted directly away from the sun. Areas north of the equator (the northern hemisphere) have shorter days and longer nights.

In Spring and Fall, the days are nearly equal in length for both the Northern and Southern Hemispheres.

Halfway in between the summer and winter solstices are the equinoxes. At these times the earth's axis is pointing neither toward nor away from the sun. On both equinoxes, all locations on earth receive exactly 12 hours of daylight and 12 hours of night.

Sunlight energy is spread evenly on the Earth.

There is a common misconception that the seasons on the Earth are caused by varying distances of the Earth from the Sun on its orbit. Some people believe that we have summer because we are closer to the Sun during that time of year. This is not correct.

Think about it: when it is summer in the Northern hemisphere it is winter in the Southern hemisphere. That is true for each season. The Southern Hemisphere is opposite the Northern.

The rotation axis of the Earth remains pointed in the same direction as it orbits the Sun.

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