The 4 SeasonsThe 4 Seasons

Many of the graphics came from Gary Becker in Allentown, PA

What causes What causes the seasons the seasons on Planet on Planet Earth?Earth?

Winter – Winter – Spring – Spring – Summer – Summer – Fall – Fall –

Galileo’s image of the Earth and Moon

Are the Seasons caused by the Are the Seasons caused by the Earths orbit?Earths orbit?

Maybe the Earth is closer to the sun in the Maybe the Earth is closer to the sun in the summer, and farther away in the winter???summer, and farther away in the winter???

Well, it’s true if you live in Chile, Argentina, Well, it’s true if you live in Chile, Argentina, Australia and other places in the southern Australia and other places in the southern hemisphere… hemisphere…

June/JulyDecember / January

March

September

So the Earth is actually closer to the sun in So the Earth is actually closer to the sun in December/January. This makes the southern December/January. This makes the southern hemisphere’s summer potentially hotter than hemisphere’s summer potentially hotter than the northern hemisphere’s.the northern hemisphere’s.

Of course, overall climate and other factors Of course, overall climate and other factors affect the real winter weather.affect the real winter weather.

The Solution!!!The Solution!!!

The Earth is tilted 23.5°The Earth is tilted 23.5°

What do you mean “tilted” – compared to what?What do you mean “tilted” – compared to what?OK, compared to the plane it makes in orbit around OK, compared to the plane it makes in orbit around the sun – it is 23.5 degrees off straight up and down.the sun – it is 23.5 degrees off straight up and down.

From a From a NorthernNorthern Hemisphere Hemisphere perspectiveperspective

What’s this “Northern Hemisphere What’s this “Northern Hemisphere Perspective” all about?Perspective” all about? The seasons are “opposite” in the Southern The seasons are “opposite” in the Southern

Hemisphere – Winter is in June-July-August and Hemisphere – Winter is in June-July-August and Summer is in December-JanuarySummer is in December-January

Look at the image again, and notice the people in Look at the image again, and notice the people in the south are “opposite”the south are “opposite”

You won’t see snow for Christmas in AustraliaYou won’t see snow for Christmas in Australia

Southern PerspectiveSouthern Perspective

WinterSummer

Vernal

Autumnal

The Suns motion during a yearThe Suns motion during a year Northern HemisphereNorthern Hemisphere

Hawaii is special Hawaii is special

Since Hawaii is just south of the Tropic of Since Hawaii is just south of the Tropic of Cancer – there are two days in the year when Cancer – there are two days in the year when the sun is directly overhead.the sun is directly overhead.

In addition, there are a number of weeks when In addition, there are a number of weeks when the sun is to the “north” of us.the sun is to the “north” of us.

Anyone living in the Tropics (between 23.5° N Anyone living in the Tropics (between 23.5° N and 23.5° S) has one or two days with the sun and 23.5° S) has one or two days with the sun directly overhead.directly overhead.

Intensity of Sunlight depends on AngleIntensity of Sunlight depends on Angle

Warmer Cooler

ShadowsShadows

Latitude, Shadows and IntensityLatitude, Shadows and Intensity At the EquinoxAt the Equinox

An Example from North An Example from North AmericaAmerica

JuneDecember

South Pole WinterSouth Pole Summer

Special LatitudesSpecial Latitudes

North PoleNorth Pole 90° N90° N Arctic CircleArctic Circle 66.5° N66.5° N Tropic of CancerTropic of Cancer 23.5° N23.5° N EquatorEquator 0° 0° Tropic of CapricornTropic of Capricorn 23.5° S23.5° S Antarctic CircleAntarctic Circle 66.5° S66.5° S South PoleSouth Pole 90° S90° S

Special DaysSpecial Days

North PoleNorth Pole Midsummer – June 21Midsummer – June 21 Arctic CircleArctic Circle June 21June 21 Tropic of CancerTropic of Cancer June 21June 21 EquatorEquator March 21 & September March 21 & September

21 21 Tropic of CapricornTropic of Capricorn December 21December 21 Antarctic CircleAntarctic Circle December 21December 21 South PoleSouth Pole Midsummer – December 21Midsummer – 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 - PolarisThe view to the North - Polaris

The view to the South – No “south polar star”

DisclaimerDisclaimerAlohaAloha

I put together these power points for use in my I put together these power points for use in my science classes.science classes.You may use them in your classes.You may use them in your classes.

Some images are public domain, some are Some images are public domain, some are used under the fair-use provisions of the used under the fair-use provisions of the copyright law, some are mine. Copyright is copyright law, some are mine. Copyright is retained by the owners!retained by the owners!

Ted BrattstromTed Brattstrom