The Reasons for the Seasons

1. The Reasons for the Seasons

2. 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 Rotation

3. 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. Night and Day Map

6. 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?

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

8. CPS Quiz • The imaginary line that runs through the north and south poles of the Earth is called the • Equator • Axis • Longitude • Latitude

9. CPS Quiz – Decide weather each example is ofA. Rotation or B. Revolution A. Rotation • 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 B. Revolution B. Revolution A. Rotation A. Rotation A. Rotation B. Revolution

10. Location and Distance in Orbit

11. 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 http://www.uwm.edu/~kahl/CoVis/Seasons/

12. Seasons

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

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

15. 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

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

17. 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)

18. 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?

19. This occurs because the Earth’s axis is tilted as it moves around the sun. This occurs when the Northern hemisphere is tilted towards the sun. This is when the length of day and night are equal. 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. Winter Summer Solstice Equinox All of the above CPS Quiz – Your answer should refer to Carrollton TX.

20. 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?