The Reasons for the Seasons

Rotation

   Earth spins on axis (imaginary line through center of Earth from North to South Pole) Rotation is counter clockwise seen from North Pole as Earth spins on its axis like a top

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Rotation - Axis

Earth tilt = 23.5

°  Axis currently pointed at Polaris (the North Star) Polaris

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Rotation

Earth rotates once every 24 hrs

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The rotation causes day & night

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Earth’s rotation causes celestial objects to appear to move from east to west in Northern Hemisphere

Night and Day Map

Just Checking… THINK…PAIR…SHARE

  What does it mean when we say the Earth rotates?

How would you define or explain the concept of Earth’s axis?

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Revolution

Movement of one object around another Earth revolves around our Sun  counterclockwise   Earth’s orbit is almost circular rather than oval shaped is still referred to as an elliptical orbit 365 ¼ days to revolve once around the Sun (~ a year) but

CPS Quiz

 The imaginary line that runs through the north and south poles of the Earth is called the A.

Equator B.

C.

D.

Axis Longitude Latitude

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CPS Quiz –

Decide weather each example is of A. Rotation or B. Revolution The Earth spinning on it’s axis.

A baseball player running around the infield.

Takes 1 year A top spinning Causes day and night.

Takes 24 hours The moon circling the Earth

Location and Distance in Orbit

Two Primary Reasons for the Seasons (on Earth)

1. angle of Sun in the sky at a given time and latitude 2. number of hours of daylight at a given time and latitude.

Handout available at http://www.uwm.edu/~kahl/CoVis/Seasons/

Seasons

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Seasons

Northern hemisphere tilts towards Sun = warmer (Summer)

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Seasons

Northern hemisphere tilts away from Sun = cooler (winter)

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Seasons

In the Spring and the Fall, the tilt of the Earth is such that the spread of sunlight shines on the Earth approximately equally

Seasons

  Southern hemisphere seasons are opposite Northern hemisphere seasons If its Winter here, then Australia is having _?_.

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Solstices

Occur twice yearly when the Sun is directly over “Tropics” (23.5°N and 23.5°S Latitude)  Summer Solstice is the longest day of the year in the Northern Hemisphere (Sun directly over Tropic of Cancer 23.5°N -at noon)  Winter solstice = shortest day of the year for Northern Hemisphere (Sun directly over Tropic of Capricorn 23.5°S -at noon) 

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Equinox

equal night & day Occurs twice each year Half-way between solstices noon sun directly over equator Sun will be at its highest point in our sky at noon but never directly overhead in Texas… why do you think this is true?

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CPS Quiz –

Your answer should refer to Carrollton TX.

This occurs because the Earth’s axis is tilted as it moves around the sun.

A.

Winter This occurs when the Northern hemisphere is tilted towards the sun.

B.

C.

Summer Solstice D.

Equinox This is when the length of day and night are equal.

E.

All of the above The shortest and longest days of the year when the noon sun is directly overhead at 23.5 degrees.

This occurs when the Northern hemisphere is tilted away from the sun.

Based on this Night and Day Map… • What season do you think it is in Carrollton?

• What time do you think it is in Carrollton?