1. © 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 3 Earth-Sun Geometry Lawrence McGlinn Department of Geography State University of New York - New Paltz

2. © 2007, John Wiley and Sons, Inc. Earth-Sun Relationship Most Physical Processes on Earth powered by incoming radiation from Sun Earth-Sun Relationship Complex – Depends on: –Latitude –Position of Sun in Sky –Time of Year –Earth’s Rotation/Axial Tilt

3. © 2007, John Wiley and Sons, Inc. Our Place in Space Speed of Light 299,792 kmps (186,282 mps) Milky Way Galaxy – 100,000 ly across Our Solar System – 11 ly across Moon is 1.28 light seconds away Gravity – mutual attracting force exerted by the mass of an object on all other objects

4. © 2007, John Wiley and Sons, Inc. The Sun About 4.6 Billion Years Old Average Star, Nothing Special 100 times diameter of Earth Powers most natural processes on Earth 8.3 min. for Sun’s energy to reach Earth Strong Magnetic Fields/Sunspots

5. © 2007, John Wiley and Sons, Inc. Shape of the Earth Insolation Variation in Sun Angle by Latitude Oblate Spheroid Subsolar Point

6. © 2007, John Wiley and Sons, Inc. At high latitudes, incoming solar radiation is spread over a larger area than at low latitudes, so energy per unit area is relatively low.

7. © 2007, John Wiley and Sons, Inc. Diffuse vs Direct Radiation

8. © 2007, John Wiley and Sons, Inc. Atmospheric Beam Depletion  Solar radiation is diminished relative to the amount of atmosphere the radiation passes through.  High solar angles see little reduction in intensity as the path from the top of the atmosphere to the surface is short.

9. © 2007, John Wiley and Sons, Inc. Solar Activity and Solar Wind Solar wind = clouds of electrically charged particles Sunspots are caused by magnetic storms. These cause changes in the solar output Sunspots have activity cycles

10. © 2007, John Wiley and Sons, Inc.Auroras

11. Auroras

12. Earth’s Orbit Around the Sun Plane of the Ecliptic One Revolution = 365.24 Days Elliptical Orbit Perihelion/Aphelion Seasons not due to distance from Sun

13. © 2007, John Wiley and Sons, Inc. S The Earth follows an elliptical orbit around the Sun with its closest point at Perihelion and its farthest point at aphelion Aphelion and Perihelion

14. © 2007, John Wiley and Sons, Inc. Viewed from above the North Pole, the Earth’s rotation and revolution are both counterclockwise. S E

15. © 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 3 The Seasons Lawrence McGlinn Department of Geography State University of New York - New Paltz

16. © 2007, John Wiley and Sons, Inc. Dimensions and Distances Earth’s orbit – Average distance from Earth to the Sun is 150,000,000 km (93,000,000 mi) – Perihelion – closest at January 3 147,255,000 km (91,500,000 mi) – Aphelion – farthest at July 4 152,083,000 km (94,500,000 mi) – Takes energy 8 min 20 sec to reach Earth – Plane of Earth’s orbit is the plane of the ecliptic

17. © 2007, John Wiley and Sons, Inc. The Seasons The Seasons Seasonality: the variation of the sun’s position over the horizon; the changing daylength during the year Seasons result from: variations in the sun’s altitude, the suns’s declination, and daylength, WHICH are dependent upon……

18. © 2007, John Wiley and Sons, Inc. Reasons for Seasons Reasons for Seasons Revolution – Earth revolves around the Sun – Voyage takes one year, roughly – Earth’s speed is 107,280 kmph (66,660 mph) Rotation – Earth rotates on its axis once every 24 hours – Rotational velocity at equator is 1674 kmph (1041 mph)

19. © 2007, John Wiley and Sons, Inc. Reasons for Seasons Reasons for Seasons Tilt of Earth’s axis – Axis is tilted 23.5° from plane of ecliptic Axial parallelism – Axis maintains alignment during orbit around the Sun – North pole points toward the North Star (Polaris) Sphericity

20. © 2007, John Wiley and Sons, Inc. The Earth’s tilt and orientation hold steady as it orbits the Sun.

21. © 2007, John Wiley and Sons, Inc. Solstice and Equinox Spring Equinox (March 20-21) – Subsolar Point – Equator Summer Solstice (June 20-21) – Subsolar Point - Tropic of Cancer – 23.5° N

22. © 2007, John Wiley and Sons, Inc. Solstice and Equinox Fall Equinox (Sept 22-23) – Subsolar Point – Equator Winter Solstice (Dec 21-22) – Subsolar Point - Tropic of Capricorn – 23.5° S

23. © 2007, John Wiley and Sons, Inc. Tropic of Capricorn Tropic of Cancer Equator Tropic of Capricorn Tropic of Cancer Equator Tropic of Capricorn Tropic of Cancer Equator Tropic of Capricorn Tropic of Cancer Equator

24. © 2007, John Wiley and Sons, Inc. Range of seasonal movement of subsolar point Tropic of Capricorn Tropic of Cancer Equator

25. © 2007, John Wiley and Sons, Inc. atitudinal change ofsubsolar points  Solar declination: latitudinal change of subsolar points

26. © 2007, John Wiley and Sons, Inc. Sun’s Arc

27. © 2007, John Wiley and Sons, Inc. The Sun as seen from 45°N in June and in December. Sun’s Arc

28. © 2007, John Wiley and Sons, Inc. Seasonal Observations

29. © 2007, John Wiley and Sons, Inc. Seasonal Observations SUMMER HEMISPHERE Carrollton = 33° What is Sun’s angle (at noon) on June 21? 90 – |(latitude – subsolar point)| 90 – | (33 – 23.5) | = 80.5 ° WINTER HEMISPHERE 90 – (latitude + subsolar point)

30. © 2007, John Wiley and Sons, Inc. Annual March of the Seasons Winter solstice – December 21 or 22 – Subsolar point Tropic of Capricorn Spring equinox – March 20 or 21 – Subsolar point Equator Summer solstice – June 20 or 21 – Subsolar point Tropic of Cancer Fall equinox – September 22 or 23 – Subsolar point Equator

31. © 2007, John Wiley and Sons, Inc. Annual March of the Seasons