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Learn about the causes of Earth's seasons, the tilt of the Earth, and how it affects the amount of sunlight received in the different hemispheres. Discover the key points and dates of each season.
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Seasons • Seasons are caused by the tilt of Earth. • No tilt means no seasons • Remember that Earth is tilted as it orbits the sun (23½ degrees). • The tilt always keeps the same angle. • Sometimes it tilts towards the sun and sometimes it tilts away. • Other times it’s not tilted either way.
From that last slide we saw that at times the North Pole faces the sun and at times (6 months later) the South Pole faces the sun. • And everyone knows that facing the sun is warmer. • So pointed towards the sun makes for summer, pointed away makes for winter.
Summer • Earth’s northern hemisphere is tilted towards the sun…so… - more direct sunlight…warmer • The southern hemisphere is tilted away from the sun….so… - less direct sunlight…colder • June 21/22 = summer solstice • Longest day of year in northern hem & shortest day in southern hemisphere
Winter • Earth’s northern hemisphere is tilted away - less direct sunlight…colder • The S hemisphere is tilted towards - more direct sunlight…warmer • Dec 21/22 = winter solstice • Shortest day of year in northern hem & longest day in southern hemisphere
Autumn • Northern hemisphere going from long days to short days (Opposite for SH). • Since Earth isn’t tilted towards or away, both hemispheres have the same amount of daylight and darkness… 12 hrs each. • This is the Autumnal or Fall Equinox • Occurs on Sept 21/22
Spring • Similar to Autumn • N hemisphere going from short days to long days (Opposite for SH). • Since Earth isn’t tilted towards or away, both hemispheres have the same amount of daylight and darkness… 12 hrs each. • This is the Spring Equinox • Occurs on March 21/22
Season Key Points • Pointed at sun = warm = summer • Pointed away from sun = cold = winter • Not pointed at = neither = fall and spring • Summer solstice = longest day of year • Winter solstice = shortest day of year • Equinoxes = equal day and night • N & S hemispheres are opposites