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