1. Chapter 2 Solar Energy to Earth and the Seasons Robert W. Christopherson Charlie Thomsen

2. Solar Energy to Earth and the Seasons The Solar System, Sun, and Earth Solar Energy: From Sun to Earth The Seasons

3. The Solar System, Sun, and Earth Solar System formation and structure Gravity Planetesimal hypothesis Dimensions and distances Speed of light Earth’s orbit

4. Gravity Mutual attracting force exerted by mass on all other objects: Solar System Formation and Structure G ≈ 6.67428×10 −11 m 3 /(kg·s 2 ). F: kg*m/s 2 =1 Newton g=9.8 m/s 2

5. Planetesimal hypothesis Sun condensed from nebular clouds 4.6 billion years ago. Big Bang ~13 billion years ago. Solar System Formation and Structure

6. Milky Way Galaxy Figure 2.1

7. Dimensions and Distances Speed of light 299,792 km/s(≈3.0×10 8 m/s) (186,282 mi/s) Milky Way Galaxy 100,000 ly across Our Solar System 11 light-hours across Moon is 1.28 light-seconds away

8. 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) Earth is 8 minutes 20 seconds from the Sun Plane of Earth’s orbit is the plane of the ecliptic

9. Our Solar System Figure 2.1

10. Pluto not a Planet since 2006 Figure 2.1 New Definition by International Astronomical Union in 2006: A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. Pluto is now called a Dwarf Planet on account of its size and the fact that it resides within a zone of other objects, known as the Kuiper Belt A dwarf planet is an object in orbit around the Sun that is large enough (massive enough) to have its own gravity pull itself into a round (or nearly round) shape. Generally, a dwarf planet is smaller than Mercury. A dwarf planet may also orbit in a zone that has many other objects in it. For example, an orbit within the asteroid belt is in a zone with lots of other objects.

11. Solar Activity and Solar Wind Diameter 1,392,000km (~109 Earths diameter ), Contain 99.86% of mass in solar system. 3/4 of Sun is hydrogen, the rest is helium (<2% of other elements, F e, O, C etc.) Nuclear fusion of hydrogen nuclei into helium, surface temp 5780 o K. The Sun orbit the galactic center once per 225~250 my. Sunspots have activity cycle of 11 years. It is indicator of solar activity. Solar wind: streams of electrically charged particles (hydrogen nuclei and free electrons) leaving the sun and can reach the Earth in 3 days. Figure 2.2

12. The Electromagnetic Spectrum Sun radiates shortwave energy Planck’s Law: Blackbody spectral radiant emittance Where h: Planck Constant, 6.626E-34 ws 2 c: speed of light in vacuum 3.0E+8 m/s : wavelength in meters T: temperature in degrees Kelvin K: Boltzman constant, 1.38054E-23 ws/K M : blackbody spectral exitance at T, unit = watts per square meter area per meter wavelength

13. The Electromagnetic Spectrum Stefan-Boltzmann’s Law: Where  is Stefan-Boltzmann constant (5.676E-8wm -2 K -4 )

14. The Electromagnetic Spectrum Wien’s Law: The wavelength at which a blackbody radiates most energy: A=2.898E-3 mK

15. Wavelength and Frequency Figure 2.5 Frequency: number of full waves passing through a point in unit time freq=c/λ

16. Particle Property Particle Properties: Radiation travels in bundles of energy unit, called photons. The photons possess particle property, most notably photons can be reflected.

17. EMR transfers in terms of energy packets or quanta in accordance with quantum theory. The particle that carries energy is called a photon. The amount of energy (Joules) carried by a single photon is Where h=6.6256E-34 J/s. It is obvious, the shorter the wavelength, the more the energy a photon carries. The total energy in a ray beam is the summation of the energy carried by all the photons that makeup the beam. Unit: Joules Energy of Photons

18. Unit: Joules/second=Watts=W Unit: Joules=J Unit of Energy Energy: Adding time energy measure: Energy flux Adding area to energy flux: energy flux density Unit: Joules/second/m 2 =W/m 2

19. The Electromagnetic Spectrum Figure 2.6

20. Solar Constant The radiant flux density at the top of the atmosphere perpendicular to the sun beam: S=1367 w/m2 Earth Top of Atmosphere Plane measuring S

21. Solar and Terrestrial Energy Figure 2.7

22. Earth’s Energy Budget Figure 2.8 Shortwave Reflected Radiation Balance Equation:

23. Distribution of Solar Radiation on Earth Surface Tropics receive more concentrated insolation due to Earth’s curvature Tropics receive 2.5× more than poles

24. Figure 2.9

25. The Seasons Seasonality Reasons for seasons Annual march of the seasons

26. Insolation at Top of Atmosphere Figure 2.10

27. Seasonality Seasonal changes Sun’s altitude – angle above horizon Declination – location of the subsolar point Daylength

28. TOA Daily Net Radiation Figure 2.11 Unit: w/m 2 Measured by Satellite (Nimbus-7) in space.

29. Reasons for Seasons Revolution Rotation Tilt of Earth’s axis Axial parallelism Sphericity

30. Reasons for Seasons Revolution Earth revolves around the Sun Voyage takes one year (365.25 days more accurately) 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)

31. Revolution and Rotation Figure 2.13

32. 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: not perfect sphere because of rotation, the equator is bulging out Sphericity: f = 1-short/long =1/298 f=? for a perfect sphere.

33. Axial Tilt and Parallelism Figure 2.14 Sun declination angle: -23.5~23.5 o

34. 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

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

37. Seasonal Observations Figure 2.18 40 o N

38. Robert W. Christopherson Charlie Thomsen Geosystems 7e An Introduction to Physical Geography End of Chapter 2