1. Where did summer go?

2. Summer at Lake Harriet Winter Carnival in St. Paul Fall at Minnehaha Park Twins Spring Training

3. Objective: You will be able to explain the reason why Minnesota progresses through four seasons in terms of the tilt of Earth’s axis and Earth’s revolution around the sun.

4. Earth moves! It spins on its axis and revolves around the sun.

5. Axis Imaginary line that passes through the earth at the North and South pole

6. Rotation Earth’s spin on its axis Rotates counter- clockwise Sun appears to move from east to west Rotation takes about 24 hours = 1 day

7. Revolution Movement of one object around another object Orbit The path an object takes as it revolves

8. Calendar A system of organizing time that defines the beginning, length and division of a year Earth’s orbit around the sun takes about 1 year Earth’s orbit takes 365 ¼ days Our calendar is based on 365 days How does that work?

9. Ecliptic: Path the sun takes across the sky Earth is tilted 23.5° from the ecliptic Meaning earth is not straight up and down Tilt = 23.5°

10. Seasons Times of the year that have predictable weather patterns and lengths of the day WHY?

11. Remember: Energy from the sun drives processes on Earth

12. Are seasons caused by Earth’s distance from the sun?

13. Tilt = 23.5°

14. Solstice Either of the two days of the year on which the sun reaches its greatest distance north or south of the equator Summer solstice on June 22 = longest day of the year Winter solstice on December 22 = shortest day of the year

15. Equinox Either of the two days of the year when the sun is directly over the equator Equinox = equal day and night Vernal equinox on March 20 Autumnal equinox on September 20

16. Because Earth’s axis is tilted the sun’s position changes over the year.

17. The tilt of Earth affects the length of the day. Longer days = more energy from sun = higher temperatures What else might the tilt of the Earth affect?

18. In summer is it warmer at 7 am or noon? Why?

19. Why is the average October temperature about 65°F at the equator, but only about 50°F in the Twin Cities?

20. What is different about sun’s rays at the equator vs. farther north? Sun’s Rays

21. Where on Earth receives more direct sunlight from a shorter distance?

22. Sun’s Rays The tilt of the axis affects the strength of sunlight in different places.

23. Because Earth’s axis is tilted the angle of incoming sunlight changes over the year.

24. Because Earth’s axis is tilted the angle of incoming sunlight changes over the year.

25. When is the sun lower in the sky? Is it cold or hot when the sun is low in the sky?

26. So, where did summer go?

27. The earth has seasons because it is tilted on its axis.