2. Earth’s rotationEarth’s rotation
• The Earth rotates on its axisThe Earth rotates on its axis
(imaginary vertical line(imaginary vertical line
around which Earth spins)around which Earth spins)
once every 24 hours.once every 24 hours.
• One day/night on Earth isOne day/night on Earth is
one rotation of the Earth.one rotation of the Earth.
• Day on Earth is when ourDay on Earth is when our
side of the Earth faces theside of the Earth faces the
sun.sun.
• Night on Earth is when theNight on Earth is when the
side of Earth we are onside of Earth we are on
faces away from the sun.faces away from the sun.
3. Earth’s RevolutionEarth’s Revolution
• It takes the Earth 365It takes the Earth 365
days (or rotations) todays (or rotations) to
travel or revolvetravel or revolve
around the Sun once.around the Sun once.
• This is called a year.This is called a year.
4. Why do we have seasons?Why do we have seasons?
• The Earth’s orbit aroundThe Earth’s orbit around
the sun is NOT a perfectthe sun is NOT a perfect
circle. It is an ellipse.circle. It is an ellipse.
• SeasonsSeasons are notare not causedcaused
by how close the Earth isby how close the Earth is
to the sun.to the sun.
• In fact, the Earth isIn fact, the Earth is
closest to the sun aroundclosest to the sun around
January 3 and farthestJanuary 3 and farthest
away from the sunaway from the sun
around July 4.around July 4.
EllipseEllipse
5. Why do we have seasons?Why do we have seasons?
• Seasons are the result of the
tilt of the Earth's axis.
• Earth’s axis is tilted 23.5°.
• This tilting is why we have
SEASONS like fall, winter,
spring, summer.
• The number of daylight
hours is greater for the
hemisphere, or half of Earth,
that is tilted toward the Sun
(experiencing summer).
6. Why do we have seasons?Why do we have seasons?
• Summer is warmer than winter (in each hemisphere) becauseSummer is warmer than winter (in each hemisphere) because
the Sun's rays hit the Earth atthe Sun's rays hit the Earth at a more direct anglea more direct angle duringduring
summer than during wintersummer than during winter
• Hemispheres experience opposite seasons (Summer inHemispheres experience opposite seasons (Summer in
Northern Hemisphere when its Winter in SouthernNorthern Hemisphere when its Winter in Southern
Hemisphere)Hemisphere)
7. Why do we have seasons?Why do we have seasons?
• During summer, the days are much longerDuring summer, the days are much longer
than the nights.than the nights.
• During the winter, the Sun's rays hit theDuring the winter, the Sun's rays hit the
Earth at an extreme angle, and the days areEarth at an extreme angle, and the days are
very short. These effects are due to the tiltvery short. These effects are due to the tilt
of the Earth's axis.of the Earth's axis.
8. Seasons in the Northern HemisphereSeasons in the Northern Hemisphere
9. SolsticesSolstices
• SolsticesSolstices occur twice a year, when the tilt of the Earth'soccur twice a year, when the tilt of the Earth's
axis is oriented directly towards or away from the Sun,axis is oriented directly towards or away from the Sun,
causing the Sun to appear to reach its northernmost andcausing the Sun to appear to reach its northernmost and
southernmost extremes.southernmost extremes.
• Winter solstice is the shortest day of the year. In theWinter solstice is the shortest day of the year. In the
Northern Hemisphere. It occurs on December 21 andNorthern Hemisphere. It occurs on December 21 and
marks the beginning of winter.marks the beginning of winter.
• The Summer Solstice is the longest day of the year. ItThe Summer Solstice is the longest day of the year. It
occurs on June 21 and marks the beginning of summer.occurs on June 21 and marks the beginning of summer.
Tyrrhenian Sea and Solstice Sky
Credit & Copyright: Danilo Pivato
10. SOLSTICESOLSTICE
• During the winter theDuring the winter the
Northern Hemisphere dayNorthern Hemisphere day
lasts fewer than 12 hourslasts fewer than 12 hours
and the Southernand the Southern
Hemisphere day lasts moreHemisphere day lasts more
than 12 hours.than 12 hours.
• During the winter solstice,During the winter solstice,
the North Pole has a 24-hourthe North Pole has a 24-hour
night and the South Pole hasnight and the South Pole has
a 24-hour day.a 24-hour day.
• The further north you goThe further north you go
during Winter, the fewerduring Winter, the fewer
hours of daylight will behours of daylight will be
experienced.experienced.
• Oppositely, the further northOppositely, the further north
you go during the Summer,you go during the Summer,
the more hours of daylightthe more hours of daylight
will be experienced.will be experienced.
http://k12.ocs.ou.edu/teachers/ref
erence/solstice.gif
11.
12. EquinoxesEquinoxes
• A day lasts 12 hours andA day lasts 12 hours and
a night lasts 12 hours ata night lasts 12 hours at
all latitudes.all latitudes.
• Equinox literally meansEquinox literally means
"equal night"."equal night".
• Sunlight strikes the earthSunlight strikes the earth
most directly at themost directly at the
equator.equator.
• This occurs twice a yearThis occurs twice a year
during Spring and Fall.during Spring and Fall. http://k12.ocs.ou.edu/teachers/reference/e
quinox.gif
13. EquinoxEquinox
• The vernal (spring)The vernal (spring)
equinox occurs Marchequinox occurs March
21.21.
• The autumnal (fall)The autumnal (fall)
equinox occursequinox occurs
September 21.September 21.
14. The Earth's seasons are not caused byThe Earth's seasons are not caused by
the differences in the distance from thethe differences in the distance from the
Sun throughout the year. They areSun throughout the year. They are
caused by the earth’s tilt and revolutioncaused by the earth’s tilt and revolution
around the sun.around the sun.
15. ReviewReview
Look closely at where the Sun is hitting theLook closely at where the Sun is hitting the
Earth during each season:Earth during each season:
http://Search.Lycos.com/setup.asp?r=5&src=clear2&query=weather+savvy
