9 9 15 9 11 15 Dr Fraunfield Chapter 2 Lecture Notes Solar Energy and the Seasons I The Solar System a Speed of light 300 000 km sec 9 5 trillion year light year i Solar system is 11 hours in diameter in light years ii Milky Way Galaxy is 100 000 light years iii Universe is 12 billion light years b Dimensions and Distances i Earth s Orbit is called plane of Earth s orbit or the plane of the elliptic 1 Average distance from Earth to the sun is 150 000 000 km or 8 minutes and 20 Doesn t affect seasons 2 The Earth is closest to the sun on January 3rd called Perihelion and it is 147 3 The Earth is furthest from the sun on July 4th called Aphelion and is 152 million seconds from the sun million km away km away II Solar Energy a Solar Activity and Solar Wind i Energy radiation coming from the sun is key to life ii Sun produces 1 Sunspots caused by magnetic storms activity cycle of 11 years little effect 2 Solar Wind streams of electrically charged particles magnetosphere defects it towards the poles otherwise it would be really harmful atmosphere ionosphere ionizes these particles which causes Aurora Borealis 3 Radiation Energy that travels in the form of electromagnetic waves a Made up of different wavelengths distance over which a wave s shape on climate repeats b Frequency number of waves unit of time c All objects radiate energy in wavelengths related to their temperature i Longer wavelengths have less frequency and are cool ii Shorter wavelengths have more frequency and are hot 9 9 15 9 11 15 Dr Fraunfield d Electromagnetic Spectrum i All objects with a temperature greater than absolute zero 0 K 273 C 460 F radiates energy ii Sun 6 000 K emits a lot of radiation shortwave radiation solar radiation iii Earth 288 K emits a lot less radiation longwave radiation terrestrial e Shortwave Radiation Emittance MUST KNOW THESE NUMBERS radiation i Ultraviolet 8 ii Visible 47 iii Infrared 45 9 9 15 9 11 15 Dr Fraunfield b Earth s Energy Budget i Solar Constant 1372 Watts m2 average amount of energy coming to the Earth from the Sun 1 Comes in as shortwave radiation 2 Goes out as longwave radiation c Incoming Energy Incoming Solar Radiation Insolation i Only one two billionth of the sun s energy is intercepted by the Earth ii Earth s curvature results in uneven insolation 1 Places where the sun s rays are perpendicular receive more insolation 2 The tropics receive the most concentrated insolation approximately 2 5 times more than at the poles In the artic regions the Earth is losing more radiation than it is gaining iii What causes Variability in Insolation 1 Sun s Position a Altitude the angle of the sun above the horizon 0 at sunrise and sunset 45 if halfway up in the sky and 90 if directly overhead b Declination the latitude of the direct overhead sun migrates seasonally i The sun can only ever be directly ahead in the tropics between 23 5 N Tropic of Cancer and 23 5 S Tropic of Capricorn c These two a b factors combined affect the intensity of insolation 2 Day Length number of hours of sunshine a Varies with Latitude b This affects the amount of insolation III Seasons a Reasons for the Seasons i Revolution 9 9 15 9 11 15 Dr Fraunfield 1 Refers to the Earth s orbit around the sun 2 Earth travels at 107 000 km hr in an elliptical orbit 3 One revolution takes 365 25 days ii Rotation 1 Spin of the Earth on its own axis 2 Rotation is counterclockwise Eastward 3 Causes daily cycle of daylight and darkness Circle of Illumination half of the Earth is always lit and the other half is dark 4 One rotation per 24 hours iii Tilt of Earth s Axis 1 Axis is tilted 23 5 from the plane of the elliptic 2 Tilt is fixed because it is independent of the time of year iv Axial Parallelism 1 Axis maintains alignment during orbit around the sun 2 North Pole points toward the North star Polaris v Sphericity b Annual March of the Seasons i Summer Solstice June 21st 1 Northern Hemisphere tilted maximally toward the sun 2 Overhead sun is at the Tropic of Cancer 23 5 N which is farthest point North it can be 3 Longest day and shortest night in the Northern Hemisphere ii Fall Equinox September 22nd 1 Neither hemisphere is tilted toward or away from the sun 2 Overhead sun is at the Equator 0 3 12 hours of day and 12 hours of night everywhere iii Winter Solstice December 21st 1 Northern Hemisphere tilted maximally away from the sun 9 9 15 9 11 15 Dr Fraunfield 2 Overhead sun is at the Tropic of Capricorn 23 5 S which is farthest point South it can be 3 Shortest day and longest night in the Northern Hemisphere iv Spring Equinox March 21st 1 Neither hemisphere is tilted toward or away from the sun 2 Overhead sun is at the Equator 0 3 12 hours of day and 12 hours of night everywhere