Transcript Seasons

Seasons
Seasons happen because of
Earth’s tilt on its axis AND
revolution around the Sun.
Axis- imaginary line drawn from
the north to the south pole.
Rotation- the spinning of the
earth on its axis. 1 rotation on
its axis =24 hours
•Revolution- the movement of the earth around the sun. Takes Earth 1
year to make one revolution.
•Orbit- the path the earth takes around the sun.
What Causes Earth’s Seasons?
Earth’s axis is tilted 23.5 degrees – it always points in the same direction
(Polaris, the North Star) as we orbit our Sun once a year
This tilt causes the hemispheres to alternate in the amount of our Sun’s light
and heat they receive through the year.
When our part of Earth (Northern Hemisphere) is tilted TOWARD the sun, we
are having summer. The NH is getting the Sun’s direct rays.
In summer, days are long, nights are short.
When our part of Earth (Northern Hemisphere) is tilted AWAY from the sun,
we are having winter. The NH is getting LESS direct rays from the sun (weak).
Days are short, nights are long.
http://www.lpi.usra.edu/education/skytellers/seasons/about.shtml
Winter Solstice
Winter Solstice- (December 21
or 22)
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The sun shines on the Tropic of
Capricorn.
The shortest day of the year will
occur on Dec. 21 or 22.
After Dec. 21 or 22 the days will
begin to get longer
Vernal Equinox
Vernal Equinox- (March 20-21)
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Sun shines directly on the
equator.
Equal hours of daylight and
darkness.
Summer Solstice
Summer Solstice- (June 20-21)
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Sun Shines directly on the Tropic of Cancer.
Longest day of the year will be June 20 or 21.
After June 20/21 the days will begin getting shorter.
Autumnal Equinox
Autumnal Equinox- (September 22 or 23)
 Sun shines directly on the Equator.
 Equal hours of daylight and darkness.
Effect of different angles of sun:
Summer solstice=rays are more concentrated
Winter solstice = rays are less concentrated, spread out
Summer solstice = hot weather on the way.
Winter solstice = cooler weather.
December
True color images
March
June
September
http://www.nasa.gov/vision/earth/features/blue_marble.html