1. Chapter 2 Solar Energy to Earth and the Seasons Robert W. Christopherson Charlie Thomsen © 2012 Pearson Education, Inc.

3. Solar Energy to Earth and the Seasons Topics in this chapter: The Solar System, Sun, and Earth Solar Energy: From Sun to Earth The Seasons Causes of the seasons

4. The Solar System, Sun, and Earth Our solar system is located in the milky way galaxy, a flattened disk shaped mass estimated to contain more than 400 billion stars. Our solar system is more than halfway out from the galatic centre in one of the milky way’s spiral arms – the Orion arm. The sun and the solar system are estimated at having formed more than 4.6 billion years ago.

5. Milky Way Galaxy Figure 2.1

6. Milky Way Galaxy Figure 2.1 © 2012 Pearson Education, Inc.

7. Dimensions and Distances Distances in space are given in light years because it is so incredibly vast. Light year: the distance that light travels in one year. At a speed of 299 792 (300 000) kmps that is a distance of about 9.5 trillion kms per year.

8. Dimensions and Distances Therefore in light years the: Milky Way Galaxy 100,000 ly across Our Solar System 11 light-hours across Moon is 1.28 light-seconds away Known universe that is observable from earth is approx. 12 billion light-years in all directions.

9. Earth’s Orbit Earth’s orbit around the sun is eliptical – a closed oval path. The orbit varies it’s distance from the sun. Earth’s average distance from the sun is approx. 150 million kms. Light from the sun reaches the earth in 8 mins 20 seconds. Earth is closest to the sun during the perihelion (SH summer – 3 Jan) and furtherest from the sun during the aphelion (SH winter – 4 July).

10. Our Solar System Figure 2.1 © 2012 Pearson Education, Inc.

11. The Sun The sun is an average star in the galaxy. Sun emits: Radiant energy Solar wind It provides all the energy for the earth and biosphere systems. Due to the tremendous pressure and temperature of the sun it’s hydrogen atoms pair together in a process of fusion. During this reaction the hydrogen forms helium and liberates enormous quantities of energy. Temperature: 6000 K (6273°C)

12. Solar Wind Consists of clouds of electrically charged particles released by the sun, containing – hydrogen and free electrons. The solar wind approaches the earth and is deflected by the earth’s magnetic field towards the magnetic poles. When this wind enters the earth’s atmosphere at the poles it results in the auroras.

13. © 2012 Pearson Education, Inc. Aurora Borealis Figure 2.4

14. Figure 2.2

15. © 2012 Pearson Education, Inc. The Sun and Sunspots Figure 2.2

16. The Electromagnetic Spectrum Sun radiates electromagnetic energy of various wavelengths. This travels at the speed of light to earth. This radiant energy is made up of different wavelengths. The sun radiates short wave radiation. The earth absorbs this and reradiates long wave radiation.

17. Wavelength and Frequency Figure 2.5 © 2012 Pearson Education, Inc.

18. The Electromagnetic Spectrum Figure 2.6 © 2012 Pearson Education, Inc.

19. Earth’s Energy Budget Figure 2.8

20. Incoming Energy - Insolation The outermost point of the earth’s atmosphere is known as the thermopause. The earth intercepts only one two-billionth of the sun’s total energy output but this supports all the earth’s systems. Insolation: the energy that enters the earth’s atmosphere. Insolation at the top of the atmosphere is referred to as the solar constant.

21. Insolation Insolation is not evenly distributed over the earth’s surface. It differs due to it’s angle and the amount of interception that occurs as it passes through the earth’s atmosphere. Subsolar point: the point on the earth receiving the most insolation which is the point at which the sun’s rays are perpendicular (90°) to the earth. This point shifts between the tropics due to seasonal change. The thermopause above the equatorial region receives 2.5 times more insolation annually than the thermopause above the poles. Due to the effect of the earth’s curvature on the angle of the sun’s rays.

22. Figure 2.9 © 2012 Pearson Education, Inc.

23. Insolation at Top of Atmosphere Figure 2.10 © 2012 Pearson Education, Inc.

24. The Seasons Seasonality Refers to the seasonal variation of the sun’s position in relation to the earth and the changing length of day and night throughout the year. This results from a change in the altitude which the sun’s rays reach above the horizon, the declination of the sun’s rays from the subsolar point and the length of day and night. At any distance from the subsolar point the radiation received is more diffuse.

25. Daily Net Radiation Figure 2.11 © 2012 Pearson Education, Inc.

26. The Seasons - Causes Seasons result from the sun’s altitude above the horizon, it’s declination and the daylength. The variations in these are caused by various physical factors: Earth’s revolution around the sun Earth’s rotation around it’s axis Tilt of the earth’s axis Axial parallelism Sphericity

27. Reasons for Seasons Revolution Earth revolves around the Sun Voyage takes one year Earth’s speed is 107,280 kmph Rotation Earth rotates on its axis once every 24 hours Rotational velocity at equator is 1674 kmph

28. Revolution and Rotation Figure 2.13 © 2012 Pearson Education, Inc.

29. Reasons for Seasons Tilt of Earth’s axis Axis is tilted 23.5° from the perpendicular to the plane of the ecliptic. Axial parallelism Axis maintains alignment during orbit around the Sun North pole points toward the North Star (Polaris) Sphericity Earth’s shape is known as a geoid (equatorial bulge and polar flattening).

30. Axial Tilt and Parallelism Figure 2.14 © 2012 Pearson Education, Inc.

31. Annual March of the Seasons Summer solstice – December 21 or 22 Subsolar point Tropic of Capricorn Autumn equinox – March 20 or 21 Subsolar point Equator Winter solstice – June 20 or 21 Subsolar point Tropic of Cancer Spring equinox – September 22 or 23 Subsolar point Equator

32. Annual March of the Seasons Figure 2.15 © 2012 Pearson Education, Inc.

33. The Four Seasons

34. Winter and Summer Solstice

35. Equinox

36. 11:30 P.M. in the Antarctic Figure 2.16

37. Midnight Sun Figure 2.17

38. Robert W. Christopherson Charlie Thomsen Geosystems 8e An Introduction to Physical Geography End of Chapter 2 © 2012 Pearson Education, Inc.