Topic 2 Solar Energy and the Seasons GEOG 203 Planet Earth R The Solar System Sun and Earth Speed of light Dimensions and distances R Solar Energy from Sun to Earth Solar activity and solar wind Electromagnetic spectrum Insolation R The Seasons Seasonality Reasons for seasons Annual march of the seasons GEOG 203 Planet Earth The Speed of Light R 300 000 km sec 9 5 trillion km year Light year Moon is 384 400 km 238 866 mi away 1 28 seconds Solar system 11 hours in diameter Milky Way Galaxy 100 000 light years Universe known observable from Earth 12 billion light years GEOG 203 Planet Earth Dimensions and Distances R Earth s orbit Plane of Earth s orbit plane of the ecliptic Average distance from Earth to Sun 150 000 000 km 8 20 minutes in light years GEOG 203 Planet Earth Earth s orbit is elliptical 3 4 Perihelion Aphelion closest on January 3 farthest on July 4 GEOG 203 Planet Earth Solar Activity 1 Sunspots 2 Solar wind 3 Energy radiation GEOG 203 Planet Earth Two Weeks in the Life of a Sunspot http www youtube com watch v SungFXUsoqw GEOG 203 Planet Earth 1 Sunspots R Caused by magnetic storms activity cycle of 11 years GEOG 203 Planet Earth GEOG 203 Planet Earth 2 Solar wind streams of electrically charged particles Magnetosphere deflects it toward poles GEOG 203 Planet Earth Aurora Borealis GEOG 203 Planet Earth Reykjanes Peninsula Southwest Iceland http www youtube com watch v H qIUE xtmo GEOG 203 Planet Earth 3 Radiation Key to life In the form of electromagnetic waves Made up of different wavelengths wavelength distance over which a wave s shape repeats frequency number of waves per unit time All objects radiate energy in wavelengths related to their temperature GEOG 203 Planet Earth Wavelength and Frequency GEOG 203 Planet Earth Electromagnetic Spectrum GEOG 203 Planet Earth Electromagnetic Spectrum R All objects with a temperature greater than absolute zero radiate energy Absolute zero 0 Kelvin 0K 273 C 460 F R Sun temperature of 6000K emits a lot of radiation Shortwave radiation aka solar radiation R Earth temperature of 288K emits a lot less Longwave radiation aka terrestrial radiation GEOG 203 Planet Earth Solar and Terrestrial Energy Radiation from Sun Radiation emitted by Earth 8 47 45 Shortwave 100 Longwave GEOG 203 Planet Earth Solar constant 1372 W m2 Earth s Energy Budget GEOG 203 Planet Earth Incoming Energy R Only one two billionth of sun s energy is intercepted by Earth incoming solar radiation in sol ation R Earth s curvature results in uneven insolation Places where the sun s rays are perpendicular receive more intense insolation Tropics receive more concentrated insolation due to Earth s curvature approximately 2 5 times more than at poles GEOG 203 Planet Earth Flashlight Analogy GEOG 203 Planet Earth What Causes Variability in Insolation GEOG 203 Planet Earth R Sun s Position Sun s Altitude angle above horizon changes in course of day 0 at sunrise sunset 45 if half way 90 if directly overhead Sun s Declination latitude of overhead sun changes in course of season sun can only ever be directly overhead in tropics s 23 5 N Tropic of Cancer 23 5 S Tropic of Capricorn affects intensity of insolation GEOG 203 Planet Earth What Causes Variability in Insolation R Daylength number of hours of sunshine varies with latitude no variability at equator greatest variability at the poles affects amount of insolation GEOG 203 Planet Earth What brings about these changes Why do we have seasons 1 Revolution 2 Rotation 3 Tilt of Earth s axis 4 Axial parallelism 5 Sphericity GEOG 203 Planet Earth 1 Revolution Reasons for Seasons refers to the earth s orbit around the sun one revolution takes 365 25 days July 4 Aphelion 152 000 000 km Perihelion 147 000 000 km January 3 GEOG 203 Planet Earth Reasons for Seasons 2 Rotation spin of Earth on its own axis rotation eastward causes daily cycle of daylight darkness circle of illumination one rotation per 24 hours GEOG 203 Planet Earth Reasons for Seasons 3 Tilt of Earth s axis axis is tilted 23 5 from plane of ecliptic Plane of Ecliptic GEOG 203 Planet Earth 4 Axial parallelism Reasons for Seasons tilt is fixed axis maintains alignment during entire orbit north pole points toward the North Star Polaris GEOG 203 Planet Earth 5 Sphericity Reasons for Seasons GEOG 203 Planet Earth TABLE 2 2 GEOG 203 Planet Earth Annual March of the Seasons R Summer solstice June 21ish North Hem tilted maximally toward sun Overhead sun Tropic of Cancer 23 5 N farthest north Longest day shortest night in North Hem R Fall equinox September 22ish Neither hem tilted toward away from sun Overhead sun Equator 0 12 hours day night everywhere GEOG 203 Planet Earth Annual March of the Seasons R Winter solstice December 21ish North Hem tilted maximally away from sun Overhead sun Tropic of Capricorn 23 5 S farthest south Shortest day longest night in North Hem R Spring equinox March 21ish Neither hem tilted toward away from sun Overhead sun Equator 0 12 hours day night everywhere GEOG 203 Planet Earth Why Do We Have Different Seasons https www youtube com watch v WgHmqv UbQ GEOG 203 Planet Earth Table Daylight Hours at Selected Northern Hemisphere Latitudes Winter Solstice Spring Equinox Summer Solstice Fall Equinox GEOG 203 Planet Earth Midnight Sun Arctic Summer Solstice GEOG 203 Planet Earth December 14 11 30 p m in the Antarctic