1. WHAT CAUSES THE SEASONS AND ASSOCIATED CHANGES IN INSOLATION?

2. September 21
December 22
June 21
SUN
March 21

3. S U N WHAT DO WE KNOW SO FAR? March & September 21 Old School
Geography N
Equator 0°
Antarctic Circle 66.5°S
Tropic of
Cancer 23.5°N
Arctic Circle 66.5°N
Capricorn 23.5 °S S
Sun on horizon z = 90°
Noon z = Lat S U N
Sun overhead z = 0°
Sun on horizon z = 90°
Gainesville, 29.5°N
Southampton, 52°N
Perth, W.A., 32°S
Zenith Angle at noon on these two
days is exactly equal to a location’s
Latitude.

4. S U N WHAT IS THE SUB-SOLAR POINT? March & September 21
Arctic C. S U N
Cancer
Equator
Sun overhead z = 0°
Capricorn
Antarctic C. S
Sub-solar point is the latitude at which the noon day Sun appears directly overhead (z=0) at noon.

5. WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD?

6. WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD?
Z = LATITUDE OF LOCATION – LATITUDE OF SUB- SOLAR POINT Thus on March and September 21: Z at Noon = Latitude of location - 0

7. WHAT IS THE SUB-SOLAR POINT FOR ANY DAY OF THE YEAR?

8. WHAT THE *%$* ?

9. WHAT THE *%$* ?
ANALEMMA

10. WHAT THE *%$* ? ANALEMMA Latitude of Sub-solar point 23.5°N Equator

11. September 21
December 22
June 21 N
SUN S
March 21

12. ANALEMMA
23.5°N
June 21

13. S S U N U N s June 21 N Sun on horizon z = 90° Sun overhead z = 0°
Cancer
Equator U
Sun overhead z = 0° N
Antarctic s
Sun on horizon z = 90°

14. S S U N U N s June 21 N Equator: z = 23.5° Sun on horizon z = 90°
Cancer
Equator U
Sun overhead z = 0° N
Equator: z = 23.5°
Antarctic s
Sun on horizon z = 90°

15. S S U N U N s WHERE IS THE SUN OVERHEAD (z=0) AT NOON? June 21 N
Sun on horizon z = 90° S U N S
Cancer
Equator U
23.5°N
Sun overhead z = 0° N
Antarctic s
Sun on horizon z = 90°

16. S S U N U N s WHAT IS NOONTIME Z IN GAINESVILLE? June 21 N
Sun on horizon z = 90° S U N S
Cancer
Z = <29.5°
= 29.5 – 23.5 = 6°
Equator U
Sun overhead z = 0°
Lat = 29.5° N
Antarctic s
Sun on horizon z = 90°
Small Zenith Angle: Sun Close To
Overhead – Higher Proportion of
Solar Constant – More Energy – HOT!

17. S S U N U N s WHAT IS NOONTIME Z IN SOUTHAMPTON? June 21 N Z = <52°
Sun on horizon z = 90° S U N S
Cancer
Z = <52°
= 52 – 23.5 = 28.5°
Equator U
Sun overhead z = 0°
Lat = 52°N N
Antarctic s
Sun on horizon z = 90°
Small Zenith Angle: Sun Closer To
Overhead – Higher Proportion of
Solar Constant – More Energy – WARM!

18. S S U N U N s WHAT IS NOONTIME Z IN PERTH, W.A.? June 21 N Lat = 32°S
Sun on horizon z = 90° S U N S
Cancer
Equator U
Sun overhead z = 0°
Lat = 32°S
Z = >32°
= = 8.5° N
Antarctic s
Sun on horizon z = 90°
Large Zenith Angle: Sun Further From
Overhead – Lower Proportion of
Solar Constant – Less Energy – COOLER!

19. September 21
December 22
June 21 N
SUN S
March 21

20. ANALEMMA
23.5°S
December 22

21. S S U N U N December 22 N s WHERE IS THE SUN OVERHEAD AT NOON?
Sun on horizon z = 90° S U N S
Arctic
Z = >0°
= = 23.5°
Sun overhead z = 0° U
Equator
Capricorn N
23.5°S
Sun on horizon z = 90° s

22. S S U N U N December 22 N s WHAT IS ZENITH ANGLE AT GAINESVILLE?
Sun on horizon z = 90°
Z = >29.5°
= = 53° S U N S
Arctic
Sun overhead z = 0° U
Equator
Capricorn N
Sun on horizon z = 90° s

23. S S U N U N December 22 N s WHAT IS ZENITH ANGLE AT SOUTHAMPTON?
Sun on horizon z = 90° S U N
Z = >52°
= = 75.5° S
Arctic
Sun overhead z = 0° U
Equator
Capricorn N
Sun on horizon z = 90° s

24. S S U N U N December 22 N s WHAT IS ZENITH ANGLE AT PERTH, W.A.?
Sun on horizon z = 90° S U N S
Arctic
Sun overhead z = 0° U
Equator
Z = < 32°
= = 23.5°
Capricorn N
Sun on horizon z = 90° s

25. WHAT IS THE SUB-SOLAR POINT TODAY?
Equator
Gainesville latitude ~ 29.5°N
Z = = 51°
Latitude of Sub-solar point
21.5°S
23.5°S

26. BOTTOM LINE

27. BOTTOM LINE
March and September: Z at noon – Lat.

28. BOTTOM LINE
March and September: Z at noon = Lat. Summer (Jun. in N, Dec. in S): Z at noon = Lat -23.5°

29. BOTTOM LINE
March and September: Z at noon = Lat. Summer (Jun. in N, Dec. in S): Z at noon = Lat -23.5° Winter (Dec. in N, Jun. in S): Z at noon = Lat +23.5°