The document discusses concepts related to the sun's path and Earth's seasons. It provides information on sunrise times, the sun's highest angle at local noon, and how Earth's axial tilt of 23.5 degrees affects seasons. The longest day of the year occurs on the summer solstice in June, when the sun's rays strike the northern hemisphere more directly, causing warmer temperatures. Seasons are due to Earth's axial tilt leading to varying declination and sunlight intensity throughout the year.

1. Announcements Last math review, tonight 4-4:45pm, room 230

2. When did the sun rise this morning? From what direction did the sun rise? yesterday

3. N S E W When did the sun rise this morning? From what direction did the sun rise? 7:15 am 113˚

4. • 76.7˚ 80.7˚• How much later (in min.) does the sun rise in Blacksburg than Williamsburg? Longitude difference = 4˚ Recall 15˚ longitude per hour 4˚/15˚ per hour = 0.267 hrs = 0.267 hrs x 60 min./hour = 16 minutes

5. N S E W What path does the sun take?

6. N S E W Local Noon For mid-latitudes in northern hemisphere sun is directly to the SOUTH At local noon the sun is at its highest angle of the day above the horizon That angle is a function of the time of year and your latitude .

7. @ 40˚ N

8. @ 40˚ N

9. @ 40˚ N

10. @ 40˚ N

12. Solstices and Equinoxes

13. June 21 st Sept 22 nd Dec 21 st Mar 21 st Earth’s position during the year: top view

14. March 21 June 21 Sept 22 Dec 21 Angle of sunlight during the year: side view

15. Arctic/Antarctic Circle Tropic of Cancer/Capricorn 23.5 o S 66.5 o S 66.5 o N 23.5 o N

16. Seasons

17. Why is there a summer season? A. Summer occurs when the distance between the earth and the sun is closest B. Summer occurs when the earth’s rotational axis is tilted towards the sun, lengthening the days C. Summer occurs because the tilt of the earth’s axis makes it closer to the sun D. Summer occurs when the sun is higher overhead, so the rays strike the Earth more directly

18. Seasons: the logic Summer longer days more direct sunlight more energy warmer temperatures Winter shorter days less direct sunlight less energy colder temperatures

19. March 21 June 21 Sept 22 Dec 21 How does a tilt make days longer or shorter?

20. 1. Day length Longitude Summer Solstice Winter Solstice Autumn Equinox Spring Equinox Winter Solstice

27. 2. Sun Angle X X X Y Y Y X’ X’= X/sinƟ Ɵ sinƟ=X/X’

28. 2. Sun Angle: insolation curves

29. 2. Sun Angle: insolation curves Winter Summer Autumn Spring Winter

30. @ 40˚ N

31. @ 40˚ N

32. @ 40˚ N

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