1. Earth’s Motions, Solar Radiation, and the Seasons

2. Rotation - The spinning of the Earth on its Axis

3. It takes the Earth 23 hours, 56min, and 4 seconds to rotate.

4. Earths Rotation Causes sunrise / sunset star trails daily events

5. The Earth Rotates in a Counterclockwise Direction (CCW)

6. Revolution - The Earth Revolves around the Sun

7. It take the Earth 365 days to Revolve around the Sun

8. Earths Revolution Causes Seasons Annual Events

10. The Earth Revolves in its orbit in a Counterclockwise Direction (CCW)

11. A. Earth's Revolution and Rotation

12. 1. The earth's orbital path is an ellipse: (a flattened out circle)

13. 2. Perihelion = point of closest approach to the sun (January) = 9
2. Perihelion = point of closest approach to the sun (January) = 9.1x107 miles

14. 3. Aphelion = point of farthest approach = 9.4x107 miles (July)

16. 4. Earth's rotation = spin about it's axis
4. Earth's rotation = spin about it's axis. Axis points to Polaris (the North Star)

17. B. Solstices and. Equinoxes Tilt of the earth's axis = 23
B. Solstices and Equinoxes Tilt of the earth's axis = always pointed to Polaris

18. Tilt

19. 1. Summer Solstice = June 21 Northern hemisphere receives the sun's light most directly (insolation) First day of summer. On the summer solstice, the direct sun rays are at =23.50 N latitude = the tropic of Cancer

20. Summer Solstice
Sunlight is most direct at the Tropic of Cancer (23.5 N) on ~ June 21.

21. SOLSTICE Summer (June 21st-ish) Sun Located at the Tropic of Cancer
Winter (December 21st-ish)
Sun Located at the Tropic of Capricorn
Tropic of Cancer
Tropic of Capricorn
Equator
Prime Meridian

22. Local Noon Shadow

24. June Solar Insolation

25. 2. Winter Solstice = December 21 Northern hemisphere receives the sun's light least directly. First day of winter. On the winter solstice, the direct sun rays are at S latitude = the tropic of Capricorn

26. Winter Solstice
Sunlight is most direct at the Tropic of Capricorn (23.5 S) on ~ January 21.

27. Local Noon Shadow

28. Solar Insolation
Energy received by the earth at various latitudes for December 21 (solstice)

30. December Solar Insolation

31. 3. Equinoxes: days in which the direct sunlight is on the equator
3. Equinoxes: days in which the direct sunlight is on the equator. Equal heating on both hemispheres. Days = nights.

32. a. Mar 21. the vernal equinox
a. Mar 21. the vernal equinox. First day of spring Direct rays of the sun are directly above the Equator.

33. b. Sept. 21: the autumnal equinox: first day of fall
b. Sept. 21: the autumnal equinox: first day of fall. Direct rays of the sun are directly above the Equator.

34. EQUINOX Equinoxes (Equal Day and Equal Night, 12 hours)
Spring (Vernal Equinox) March 21st-ish
Fall (Autumnal Equinox) September 21st-ish
Sun Located on Celestial Equator (Earth’s Equator)
Tropic of Cancer
Tropic of Capricorn
Equator
Prime Meridian

35. Equinox Shadow
Sun rises
due East,
Sun sets
due West

37. 4. Solar Declination: latitude where the noontime sun is directly overhead, on any given day.

38. 5. Factors that affect the amount of insolation we get.

39. a. Amount of daylight: longer day => more heat shorter day => less heat Artic Circle = N lat. no day in winter, no night in summer.  Antarctic Circle = 66.50S lat.

40. Day Light Hours (Solstice)

41. Day Light Hours (Equinox)

42. Day Light Hours

43. b. Solar angle:The smaller the solar angle, the more the beam is spread out => less intensity => less heat

44. Changing Aspect Angle
Direct Sunlight is more intense and concentrated.
Solar Incidence Angle is Latitude and Time Dependent
Seasonal and Diurnal

45. c. Beam Depletion: Some of the sun's light is reflected back into space, and some is absorbed. The rest goes through.

47. Incident Angle

50. Earth’s Circle of Illumination
50 % of the earth’s
surface is illuminated
by the sun,
every hour
of every day.

52. Altitude-Azimuth - Angle of the sun above the Horizon
Zenith
Ecliptic (Path of the Sun)
NCP
34 degrees N S W

53. Zenith – Position Directly Overhead
There is much less atmosphere to travel through directly overhead than on the horizon. The sun is more direct and intense.

54. Horizon – Point where the land meets sky
By the time the sun gets on the horizon, it is at a grazing angle and heavily scattered, refracted and absorbed.

56. Thermal Energy For Any Given Latitude
Maximum Daily Solar Insolation Occurs At
Hottest Hour of the Day (on average)
Maximum Monthly Solar Insolation Occurs
Hottest Month of the Year (on average)

57. Thermal Energy Noon 2 - 4 pm June August For Any Given Latitude
Maximum Daily Solar Insolation Occurs At
Hottest Hour of the Day (on average)
Maximum Monthly Solar Insolation Occurs
Hottest Month of the Year (on average)
Noon
2 - 4 pm
June
August

59. GLOBAL VARIATIONS in INSOLATION
Insolation received at the earth’s surface varies with latitude. The higher angle of the sun in the sky at the equator conveys more energy per unit area than at higher latitudes.
A given amount of radiation covers a smaller area when overhead than when at a low angle; it is more concentrated
Radiation passes through a greater length of atmosphere when at a low angle in the sky than when overhead. Atmospheric gases, dust and vapour absorb more energy before it reaches the earth’s surface.
Low sun (as sunset) shows more red due to atmospheric dust and pollution
A high sun is more effective than a sun low in the sky

60. Lengths of day and night vay more between the seasons at higher latitudes. This makes climate more seasonal at the poles than the equator
DAY LENGTH
Six months daytime (March-Sept), six months night (Sept - March)
One day with 24 hours daylight (June 21st); one day with 24 hours darkness (Dec 21st)
North Pole 90°N
Arctic circle 66.5°N
Sun is overhead once a year (June 21st). Day length always at least 10 hours.
More seasonal
Tropic of Cancer 23.5°N
Constant day length - 12 hours day and night all year round
Equator 0°
Tropic of Capricorn 23.5°N
More seasonal
Sun is overhead once a year
(Dec 21st). Day length always at least 10 hours.
Antarctic circle 66.5°S
One day with 24 hours daylight (March 21st); one day with 24 hours darkness (June 21st)
South Pole 90°N
Six months daytime (Sept - March), six months night (March-Sept)

63. Seasonal Orientations