What Causes Seasons?

We know that the reason we have day and night is because the Earth rotates.

Rotate means

to turn.

The Earth rotating on its ______gives us day and night.

axis

Earth’s axis isthe imaginary line that goes through the center of the Earth.

But guess what! Rotating isn’t the only way the Earth moves in space!

The Earth also revolves.

Revolve – When one object moves around another object

It takes the Earth one year, or 365 ¼ days to orbit the sun.

Does anyone know what orbit means?

Orbit -

The path that an object follows as it revolves around another object.

How long does one revolution take?

• Low Latitude-– Almost always hot.– Between Tropic of Cancer and Tropic of Capricorn. – Direct sunlight

• Middle Latitude-– Periods of cool and warm temperatures.– Have seasons of Spring, Summer, Fall and Winter

lasting 3 months.

• High Latitude-– Are very cool and bitterly cold.– Polar zones – Very little sunlight

• Tropic of Cancer- 23 ½ N Sun shines directly above June 21 or 22.

• Tropic of Capricorn-23 ½ S Sun shines directly above December 21 or 22.

• Arctic Circle- 66 ½ N

• Antarctic Circle- 66 ½ S

High

Middle

Low

High

Middle

But why do we have four seasons?

It’s because the Earth’s axis is tilted.

Take a good look at our globe. It‘s not tilted like that because it looks nice. No way. That’s the way the Earth is tilted in space.

That tilt gives us seasons!

Look at this diagram. Notice how the Earth is always tilted in the same direction. As the Earth __________ the part of Earth tilted toward the sun changes.

revolves

During part of the year the North Pole tilts towards the sun. This season is ________.summer

During another part of the year, the North Pole points away from the sun. This season is ______.winter

•Sun directly over Tropic of Capricorn.

•Winter Solstice December 21or 22

•Sun directly over Tropic of Cancer

•Summer Solstice June 21 or 22

•March 21 or 22 sun shines strongest near equator.

•Equal amount of sun in each hemisphere

•September 21 or 22 sun shines strongest near equator.

•Equal amount of sun in each hemisphere

Key Concepts

• If the Earth’s rotation were slower how would it affect the cycle of day and night?

• If the Earth was not tilted what would happen?

Key Concepts

• Why are seasons different in the Northern Hemisphere and Southern hemisphere?

Because of the tilt of the Earth’s axis, the two hemispheres receive different amounts of sunlight during the year.

Key Concept

• What causes the Earth to have seasons?

The difference in the amount and intensity of sunlight during the course of a year results in different seasons.

Critical Thinkingor Understanding what we learned and

applying

• What would happen to plant and animals life if the Earth did not tilt on its axis? Why?