Download Chapter 24.2 The Sun and the Seasons

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Earth moves in 2 ways: Rotation (spinning of
the Earth’s axis) and Revolution (Movement
of one body in space around another)
Earth’s rotation causes day/night, as Earth
rotates from west-east, the sun appears to
move from east-west
As Earth continues to spin toward the east,
the sun sets in the west and night falls
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As Earth rotates on its axis, it also travels
around the sun
It takes about 365 ¼ days to complete a full
revolution around the sun (Called an Earth
year)
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Different parts of the Earth receive different
amounts of sunlight depending on their
latitude (measures distance in degrees
north or south of the equator)
Regions near the equator receive more
sunlight than the poles
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Scientists use lines of latitude to mark out 3
different types of regions within which
temperature are generally similar (tropic,
temperate, polar zones)
23.5° south-23.5° north =tropic zone
23.5° north-66.5°north and from 23.5° south66.5° south=temperate zones
66.5° north-North Pole and from 66.5° southSouth Pole=polar zones
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Most of the United States is in the temperate
zone
What causes the seasonal changes? The
seasons are caused by the tilt in the Earth’s
axis as it moves around the sun (Earth tilted
23.5°)
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Because the tilt in the Earth’s axis, the
latitude at which the noon sun appears
directly overhead changes each day
A solstice occurs on 2 days each year when
the sun is directly overhead at latitude 23.5°
north or 23.5° south
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In the northern hemisphere the summer
solstice begins around June 21st (start of
summer, tilted towards sun, daylight hours
longer)
In the northern hemisphere 6 months later on
about December 21st the winter solstice
marks the beginning of winter (tilted away
from sun, daylight hours shorter)
Seasons affected by the tilt of the Earth not
where it is in its orbit
Marks the beginning or spring and autumn
(halfway between the solstices)
 At an equinox neither hemisphere is tilted
toward the sun, and the lengths of the
days/nights are equal
 The vernal equinox which occurs about March
21st in the northern hemisphere marks the start
of spring
 The autumnal equinox which occurs about
September 22nd in the northern hemisphere
marks the star of autumn (Noon sun is directly
overhead at the equator)
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