The 4 Seasons
Many of the graphics came from Gary Becker in Allentown, PA
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What causes
the seasons
on Planet
Earth?
Winter –
Spring –
Summer –
Fall –
Galileo’s image of the Earth and Moon
Are the Seasons caused by the
Earths orbit?
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Maybe the Earth is closer to the sun in the
summer, and farther away in the winter???
Well, it’s true if you live in Chile, Argentina,
Australia and other places in the southern
hemisphere…
September
December / January
June/July
March
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So the Earth is actually closer to the sun in
December/January. This makes the southern
hemisphere’s summer potentially hotter than
the northern hemisphere’s.
Of course, overall climate and other factors
affect the real winter weather.
The Solution!!!
The Earth is tilted 23.5°
What do you mean “tilted” – compared to what?
OK, compared to the plane it makes in orbit
around the sun – it is 23.5 degrees off straight up
and down.
From a Northern Hemisphere
perspective
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What’s this “Northern Hemisphere
Perspective” all about?
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The seasons are “opposite” in the Southern
Hemisphere – Winter is in June-July-August and
Summer is in December-January
Look at the image again, and notice the people in
the south are “opposite”
You won’t see snow for Christmas in Australia
Southern Perspective
Vernal
Summer
Winter
Autumnal
The Suns motion during a year
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Northern Hemisphere
Hawaii is special 
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Since Hawaii is just south of the Tropic of
Cancer – there are two days in the year when
the sun is directly overhead.
In addition, there are a number of weeks when
the sun is to the “north” of us.
Anyone living in the Tropics (between 23.5° N
and 23.5° S) has one or two days with the sun
directly overhead.
Intensity of Sunlight depends on Angle
Warmer
Cooler
Shadows
Latitude, Shadows and Intensity
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At the Equinox
An Example from North America
December
South Pole Summer
June
South Pole Winter
Special Latitudes
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North Pole
Arctic Circle
Tropic of Cancer
Equator
Tropic of Capricorn
Antarctic Circle
South Pole
90° N
66.5° N
23.5° N
0°
23.5° S
66.5° S
90° S
Special Days
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North Pole
Midsummer – June 21
Arctic Circle
June 21
Tropic of Cancer
June 21
Equator
March 21 & September 21
Tropic of Capricorn
December 21
Antarctic Circle
December 21
South Pole
Midsummer – December 21
Note – I’ve said the 21st, but there is some variation – sometimes 22nd or even 23rd it has to do with leap years and the fact that a year is actually 365.25 days long
The view to the North - Polaris
The view to the South – No “south polar star”
Disclaimer
Aloha
I put together these power points for use in my
science classes.
You may use them in your classes.
Some images are public domain, some are
used under the fair-use provisions of the
copyright law, some are mine. Copyright is
retained by the owners!
Ted Brattstrom