Day 11

1. Day 11 Sun – Earth System Investigation 3 part 2

2. Review • Review the following questions from “Wendy and Her Worldwide Weather Watchers”: • When one location on Earth has 14 hours of daylight, is all the rest of the world having 14 hours of daylight as well? • Is the longest day of the year the same length all over the world?

3. Review • Is the shortest day of the year the same day all over the world? • Are the longest days always in the summer? • Are the shortest days always in the winter?

4. Why? • What ideas do you have to explain why daylight hours change over a year?

5. Sun-Earth Model • Represent the Earth and the Sun • How should I set up the model?

6. Sun-Earth Model

7. Revolution The movement of one object around another Takes 365 days or 1 year The Earth revolves around the Sun

8. Rotation The Earth turning on its axis One turn on it axis takes 1 day or 24 hours Earth has a North and South Pole Axis is the imaginary line that if you connect the North and South Pole The axis is tipped over at an angle of 23.5˚

9. Rotation • How do we know where it is day and where it is night on this globe? Day Night • How much of the globe is in daylight at any given time? • Always exactly half illuminated and half dark

10. North Star (called Polaris) Always positioned directly over Earth’s North Pole Used as a navigation aid to seafarers and explorers for centuries

11. Summary • Is there a part of Earth that experiences only daylight or only darkness during the year? Above the Arctic Circle Below the Antarctic Circle

12. Equinox Two days during the year that day and night hours are equal Comes from Latin meaning “equal night”

13. Autumnal equinox occurs around September 21 Fall Equinox Vernal equinox occurs around March 21 Spring Equinox

14. Longest Day in the Northern Hemisphere? • Which way is the North Pole tilted? • Toward the Sun

15. Solstices Summer Solstice Winter Solstice Around June 21 The longest day of the year Solstice means “sun stands still” Around December 21 The shortest day of the year

16. At fall equinox North Pole is tilted neither toward nor away from the Sun Sun is directly over the equator Half in daylight and half in darkness • At spring equinox • Sun is directly over the equator • Day and night are equal • At summer solstice • North Pole is tilted toward the Sun • Northern Hemisphere receives more sunlight • At summer solstice • North Pole is tilted toward the Sun • Northern Hemisphere receives more sunlight • At summer solstice • North Pole is tilted toward the Sun • Northern Hemisphere receives more sunlight • At winter solstice • North Pole is now tilted away from the Sun • Shortest day of the year

17. At fall equinox • Days are getting shorter • Less exposure to light, lower temperatures • At winter solstice • Days are shortest • Less exposure to light, lower temperatures • Snow, ice, frost, etc • At summer solstice • Days are longer • Longer exposure to light produces the effects of summer • Warmer temperatures, plant growth Seasons • At spring equinox • Days are getting longer • Exposure to light is increasing, raising temperatures

18. Reading • Read “Seasons” starting on page 17 of your green resource book.