1. Seasons on Earth All Figures from http://www.fourmilab.ch/earthview/v planet.html By Diana L. Duckworth Rustburg High School Campbell County, VA

2. Three Factors Cause Seasons Tilt of Earth at 23.5 degrees latitude –Greater tilt - more extreme seasons –Less tilt - less extreme seasons Revolution of Earth around Sun –Elliptical orbit –Perihelion - January –Aphelion - July Parallelism of Axis of Rotation –Axis always points toward Polaris

3. Tilt of Axis Causes sun to be directly overhead at a different latitude each day Summer Solstice @ 23.5N (~June 21) –More daylight & more intense radiation in Northern Hemisphere Winter Solstice @ 23.5S (~December 21) –More daylight and more intense radiation in Southern Hemisphere Equinox (twice a year) @ Equator –Days & Nights are 12 hours each everywhere

4. Key to Figures In the following illustrations, the dark area represents the 50% of the earth that is in darkness and the light areas represent the 50% of the earth that is in daylight. In all figures, the sun can be considered to be in the geographic center of the image.

5. Equinox 0Z

6. Equinox 3Z

7. Equinox 6Z

8. Equinox 9 Z

9. Equinox 12Z

10. Equinox 15 Z

11. Equinox 18Z

12. Equinox 21Z

13. Equinox 24Z

14. Summer Solstice 0Z

15. Summer Solstice 3Z

16. Summer Solstice 6Z

17. Summer Solstice 9Z

18. Summer Solstice 12Z

19. Summer Solstice 15Z

20. Summer Solstice 18Z

21. Summer Solstice 21Z

22. Summer Solstice 24Z

23. Winter Solstice 0Z

24. Winter Solstice 3Z

25. Winter Solstice 6Z

26. Winter Solstice 9Z

27. Winter Solstice 12Z

28. Winter Solstice 15Z

29. Winter Solstice 18Z

30. Winter Solstice 21Z

31. Winter Solstice 24Z

32. Tilt of Axis Locates Key Latitudes Tropic of Cancer - where Sun’s rays are vertical at Summer Solstice = tilt 23.5N Tropic of Capricorn - where Sun’s rays are vertical at Winter Solsltice = tilt 23.5S Arctic Circle - latitude of total daylight at Summer Solstice or darkness at Winter Solstice –90 - tilt = 90N - 23.5N = 66.5N Antarctic Circle - latitude of total daylight at Winter Solstice or darkness at Summer Solstice –90 - tilt = 90S - 23.5S = 66.5S

34. 7 AM Nov 7, 2004 Sun @ 16°28’ S

35. Winter Solstice view from Sun

36. Equinox view from Sun

37. Summer Solstice view from Sun

38. Summer Solstice view from Moon

39. Equinox view from Moon

40. Winter Solstice view from Moon

41. As the World Turns Rotation has nothing to do with seasons!

49. Changes with the Seasons Maximum elevation of sun & position in sky from Northern Hemisphere –June to December - gets lower & farther to South –December to June - gets higher & farther to North Length of Daylight –June to December - daylight gets shorter –December to June - daylight gets longer