Why do we have days?

1. Warm-Up March 15 Why do we have days? We have day and night because the Earth rotates on its axis.

2. Sunlight Sunlight By the way . . . When where you are is pointed toward the Sun, it is day. Then the Earth rotates you away from the Sun, and it is night. Daytime Nighttime

3. Learning Standard: Today I’m creating a model to show the tilt of Earth on its axis because it explains what causes seasons. Opening: Luck of the Draw (questions about seasons) Work Session: Notes about seasons Cut and paste activity - seasons Closing: Homework – Seasons worksheet

4. What is a season? One of the major divisions of the year, generally based on cyclic (recurring) changes of climate. Spring, Summer, Fall, and Winter Occurs in both the Northern and Southern Hemispheres (just at different times of the year). Luck of the Draw Seat 20

5. What causes the seasons? The earth is tilted on it’s axis at 23.5˚. Luck of the Draw Seat 2

6. What’s the difference betweenrotation and revolution? Revolution is when one object orbits another. Rotation is when an object turn around. Luck of the Draw Seat 12

7. Before we continue, let’s review

8. Important Latitudes to remember

9. Why is earth tilted at 23.5°? • No one knows… • Astronomers have different theories: • About 5 billion years ago, when the Earth was still very young, it was struck by a Mars-sized planet. This impact could have tipped our planet over. • As the cloud of dust and gas collapsed when the universe was forming, the solar system did not form uniformly, the spinning of the gases and other planets is what made each different, hence the tilting of the planets • Essentially, the numerical value of this axis tilt is an artifact of the way the Earth formed. It didn't have to have any specific value, and in fact the other planets all have different axis tilts owing to the differing details of their formation.

10. What would happen if earth wasn’t tilted? • Earth is tilted at 23.5 degrees, Uranus is tilted at about 98 degrees • If you were standing on Uranus (if you could) the only difference you would notice was that the sun and the other planets would appear to rise and set in the north and south rather than east/west like on Earth. • Whatever the reason, it's a good thing - if the Earth did not tilt, countries near the poles would be cold and dark all year round. If it tilted too much, the seasons would be very extreme – like on the planet Uranus. Here the winter lasts for 42 years in total darkness http://www.madsci.org/posts/archives/nov99/943922199.Es.r.html

11. What does the tilt do? • It allows the sun’s rays to shine more directly andfor longer periods of time on some locations than other places of Earth.

12. Who gets the most sun? Sun Over Equator (March 21) Sun Over Tropic of Cancer (June 21) Sun Over Tropic of Capricorn (December 21) Sun Over Equator (September 21)

13. Sunlight Reaching Earth at… • Winter Solstice • Longest day of the year in the Northern Hemisphere. Shortest day of the year in the Southern Hemisphere.

14. Tilt of Earth and Days • The length of a day changes because the earth spins at a tilt and the Sun’s rays hit the earth more directly at different times of the year. Summer solstice (June 21) Northern Hemisphere -The day is longer than 12 hours Southern Hemisphere - The day is shorter than 12 hours North Pole has a 24-hour day South Pole has a 24-hour night.

15. What happens during the Equinox? Latin – equal) The day and night have an EQUAL amount of sunshine. The Sun’s rays hit the earth more directly at the equator.

16. Earth is ALWAYS tilted to the right.

17. Word Bank for homework • Sunlight Summer Solstice Length • Revolution Closer Longer • September 22 More time Spring • Southern Away Indirect • Autumn Directly Nights