1 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 calledthe plane of the ecliptic Solar Energy: From Sun to Earth ? Solar Activity and Solar Wind ? Electromagnetic Spectrum of Radiant Energy ? Intercepted Energy at the Top of the Atmosphere Solar Activity and Solar Wind 2 Solar Wind ? The sun blows out a constant stream of particles called the solar wind ? The particles travel at a speed of around 400km/s- takes about 3 days to reach earth ? The wind is a plasma of electrons, and hydrogen and helium ions http://www.n3kl.org/sun/noaa.html Magnetic Field of the Earth 3 Aurora ? Lights seen in the atmosphere in Northern and southern latitudes ? Auroras are strong during geomagnetic storms caused by the solar wind 4 Ion (solar wind) interaction with magnetic field 5 Jupiter has auroras too. The Electromagnetic Spectrum Figure 2.5 Figure 2.6 Ways to label radiation ? By its source ? Solar radiation - originating from the sun ? Terrestrial radiation - originating from the earth ? By its proper name ? ultra violet, visible, near infrared, infrared, microwave, etc?. ? By its wavelength ? short wave radiation ??3 micrometers ? long wave radiation ? > 3 micrometers 6 Electromagnetic Spectrum http://www.walter-fendt.de/ph11e/emwave.htm The electromagnetic spectrum of the sun 7 Radiation: basic laws ?Stefan Boltzman law: (E = ? T 4 ) (E is in Watts/m 2 ) As T increases, E increases by a power of 4. If T doubles, E increases by 16 times! ?Wien?s law: l max ~ 3000/T (l max is in Ám and T is in Kelvin) Wavelength of peak radiation emitted by an object is inversely related to temperature 4 E T?= Spectrum of the sun compared with that of the earth Figure 2.7 The Electromagnetic Spectrum ? Sun radiates shortwave energy ? Shorter wavelengths have higher energy ? Earth radiates longwave energy 8 Distribution of Insolation ? Tropics receive more concentrated insolation due to the Earth?s curvature ? Tropics receive 2.5X more than poles Figure 2.9 9 Earth?s Energy Budget Figure 2.8 Daily Net Radiation The Seasons ? Seasonality ? Reasons for Seasons ? Annual March of the Seasons Revolution and Rotation Figure 2.13 10 Seasonality ? Seasonal changes ? Sun?s altitude ? angle above horizon ? Declination ? location of the subsolar point ? Daylength Reasons for Seasons ? Revolution ? Rotation ? Tilt of Earth?s axis ? Axial parallelism ? Sphericity Reasons for Seasons ? Revolution ? Earth revolves around the Sun ? Voyage takes one year ? 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) 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 11 Axial Tilt and Parallelism Figure 2.14 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 12 Annual March of the Seasons Figure 2.15 Midnight Sun Figure 2.17 Seasonal Observations Figure 2.18 Mark Microsoft PowerPoint - solar
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