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Ch 24-2
Sun and seasons
Earth• The Earth moves in two ways
–Rotation – the Earth’s spinning on its’ axis•This causes day and night•Takes 24 hours to complete
–Revolution – Movement around the sun•This causes the seasons•Takes 365 1/4 days to complete
Latitude Zones• Latitude measures degrees north and south
of the equator– 0 degrees is equator, 90 degrees are the
poles– Three regions
• Tropics below 23.5 degrees north and south
• Temperate between 23.5 and 66.5 degrees
• Polar above 66.5 degrees
Seasons• The Earth’s axis is tilted 23.5 degrees.
• As Earth orbits the sun its axis changes relative to the sun
• At some point the sun is closer to the north tropic line (our summer) and southern tropic (our winter)
• The seasons are caused by the tilt of the Earth’s axis as it moves around the sun.
Seasons• Solstice occurs twice a year when the
sun is directly overhead of 23.5 degrees
• June 21 summer solstice longest day of sun, December 21 winter solstice shortest day of sun
• Equinox occurs twice a year when the sun is directly above the equator.
• March 21 spring equinox, September 22 is Autumn equinox
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