1. The Reasons for the Seasons

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

3. Rotation - Axis Earth tilt = 23.5°
Polaris
Rotation - Axis
Earth tilt = 23.5°
Axis currently pointed at Polaris (the North Star)

4. Rotation Earth rotates once every 24 hrs
The rotation causes day & night
Earth’s rotation causes celestial objects to appear to move from east to west in Northern Hemisphere

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

6. Two Primary Reasons for the Seasons (on Earth)
angle of Sun in the sky at a given time and latitude
number of hours of daylight at a given time and latitude.
Handout available at

7. Seasons

8. Seasons
Northern hemisphere tilts towards Sun = warmer (Summer)

9. Seasons
Northern hemisphere tilts away from Sun = cooler (winter)

10. 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

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

12. 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)

13. 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?

14. Click on “Seasons” to watch the animated video:

15. Sketch and label the diagram: