Download Seasons

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.
We always point to the North Star when we
orbit the sun
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
