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Unformatted text preview: Chapter 2 Solar Energy, Seasons, and the Atmosphere • The Solar System, Sun, and Earth • Solar Energy: From Sun to Earth • The Seasons Milky Way Galaxy • Our solar system located on trailing edge of Milky Way Galaxy • Disk-shaped mass of nearly 400 billion stars Nebular/Planetisimal/Dust-Cloud Hypothesis • Solar system condensed from a large, slowly rotating cloud of dust and gas, a nebula • The force of gravity caused dust and gas particles to condense into suns and planets • Planets accumulated additional dust, gases and icy comets • Formation of Sun and its solar system dates to 4.6 billion years ago Solar System Formation and Structure • Gravity – Mutual attracting force exerted by mass on all other objects • Planetesimal hypothesis – Suns condense from nebular clouds Speed of Light • 299,792 kmps (186,282 mps) ca. 186,000 • Light-year = distance that light travels in a year = 6 trillion miles • Known universe is 12 billion light-years across • Milky Way Galaxy 100,000 ly across • Our Solar System is 11 light-hours across • Moon is 1.28 light-seconds away (238,866 mi) • Think of this when you look at the stars at night… Solar Energy • Sun produces thermonuclear energy • Atoms of hydrogen are forced together under intense heat and pressure • Pairs of hydrogen nuclei are fused and enormous quantities of energy are released • Principal outputs are radiant energy and solar wind • Sun has used up about ½ of the hydrogen in its core – in 5 BY, it will run out of hydrogen fuel • Sun provides Earth with radiant energy, which travels to Earth at speed of light • This energy flows outward from the sun in the form of electromagnetic waves • Only a tiny fraction of sun’s energy output is intercepted by Earth – about one/two-billionth • Solar energy that reaches the Earth is termed insolation • Solar constant = average value of insolation received at thermopause = 1372 W/m 2 Electromagnetic Waves • Electromagnetic waves classified on the basis of wavelength – the distance from the crest of one wave to the crest of the next • Hot bodies radiate (mostly) shortwaves • Cool bodies radiate (mostly) long waves • Wavelengths are measured in micrometers • Dividing line between shortwave and long-wave radiation is about 4 micrometers (&m = 1 millionth of a meter) • Sun’s energy in ultraviolet, visible and shortwave infrared portions of spectrum • Earth outputs heat to outer space in longer wavelength, thermal infrared waves Solar and Terrestrial Energy Distribution of Insolation • Angle of solar rays varies by latitude Æ uneven global distribution of insolation • Subsolar point = receives insolation perpendicular to the surface (sun is directly overhead) = remember well at Syene • Subsolar point ranges from 23.5 o N to 23.5 o S • Tropics receive more concentrated insolation due to the Earth’s curvature • Tropics receive 2.5x more than poles Global Net Radiation • Net radiation is balance between incoming shortwave and outgoing long wave...
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This note was uploaded on 04/20/2008 for the course GEOS 200 taught by Professor Hanchette during the Spring '08 term at University of Louisville.
- Spring '08