Slide 1Learning ObjectivesMilky Way GalaxyDimensions and DistancesOur Solar SystemEarth’s OrbitWhat is Solar Energy?SunspotsSunspots and Solar WindAurorasSolar RadiationThe Electromagnetic Spectrum of Radiant EnergySolar and Terrestrial Energy Distribution by WavelengthEarth’s Energy BudgetInsolationDistribution of InsolationInsolation Receipts and Earth’s Curved SurfaceInsolation at Top of AtmosphereAverage Daily Net RadiationThe Seasons Five Reasons for SeasonsReasons for Seasons Revolution and RotationReasons for Seasons Axial Tilt and ParallelismAnnual March of the SeasonsAnnual March of the SeasonsSeasonal ObservationsSummary of Chapter 2End of Chapter 2© 2015 Pearson Education, Inc.Chapter 2 LectureSolar Energy to Earth and the Seasons Geosystems9th Edition© 2015 Pearson Education, Inc.Learning Objectives•Distinguish between galaxies, stars, and planets.•Locate Earth in the Solar System and Galaxy.•Summarize the origin, formation, and development of Earth.•Reconstruct Earth’s annual orbit about the Sun.•Describe the Sun’s operation.•Explain the characteristics of the solar wind.•Explain the characteristics of the electromagnetic spectrum of radiant energy.•Illustrate the interception of solar energy and its uneven distribution at the top of the atmosphere.•Define solar altitude, solar declination, and daylength.•Describe the annual variability of solar altitude, solar declination, and daylength—Earth’s seasonality.© 2015 Pearson Education, Inc.Milky Way Galaxy© 2015 Pearson Education, Inc.Dimensions and Distances•In astronomy, what is the unit we use for distance?–light-year: distance that light travels in one year –light speed:300,00 km/s –1 light-year (ly) = 9.5 trillion km–Light year is an unit of distance.© 2015 Pearson Education, Inc.Our Solar System© 2015 Pearson Education, Inc.Earth’s Orbit•Earth’s orbit around the Sun is presently elliptical— a closed oval path .•Plane of Earth’s orbit about the Sun is called the plane of ecliptic.•Average distance from Earth to the Sun is 150,000,000 km. •Light reaches Earth from the Sun in about 8 minutes and 20 seconds. •Perihelion—closest on January 3 –147,255,000 km •Aphelion—farthest on July 4–152,083,000 km© 2015 Pearson Education, Inc.What is Solar Energy?•Energy is the capacity of a physical system to do work. The unit is Joule(J) •Solar energy is radiant energy (i.e., radiant light and heat) from the Sun.•Solar energy is generated by the nuclear fusion reaction process in which pairs of hydrogen nuclei are joined, form helium, and emit a large amount of energy.© 2015 Pearson Education, Inc.Sunspots •Sunspots are caused by magnetic storms on the sun. – They are more than 12 times Earth’s diameter.•Their temperatures are less than the temperatures of their surroundings. •Sunspots have an activity cycle of 11 years.© 2015 Pearson Education, Inc.Sunspots and Solar Wind•Sunspots can produce the solar wind.• is clouds of electrically charged particles, and takes about 3 days to reach Earth.•The magnetosphere deflects the solar wind toward both of Earth’s poles and only a small portion of it enters the atmosphere and produces auroras.© 2015 Pearson Education, Inc.Auroras© 2015 Pearson Education, Inc.•Solar radiation occupies a portion of the electromagnetic spectrum of radiant energy.•This radiant energy travels at the speed of light to earth .–Light reaches Earth from the Sun in about 8 minutes and 20 seconds. •The total spectrum of this radiant energy is made up of different wavelengths. Solar Radiation© 2015 Pearson Education, Inc.The Electromagnetic Spectrum of Radiant Energy•High frequency is associated with small wavelengths and high energy •Solar radiation consists of three parts:1) Gamma rays , X-rays, UV (8%)2) Visible light(47%)3) infrared (45%)© 2015 Pearson Education, Inc.Solar and Terrestrial Energy Distributionby Wavelength• High energy (or shortwave radiation) is associated with high temperature.• Low energy (or longwave radiation) is associated with low temperature.© 2015 Pearson Education, Inc.Earth’s Energy Budget© 2015 Pearson Education, Inc.Insolation•Solar radiation that reaches a horizontal plane at Earth is called onsolation, i.e., incoming solar radiation.•Insolation at the top of the atmosphere is expressed as the solar constant (1372W/m2).© 2015 Pearson Education, Inc.Distribution of Insolation•The thermopause (480 km) above Earth’s surface is the outer boundary of Earth’s energy system. •Earth only receives one two-billionth of Sun’s total energy output.• Tropics receive more concentrated insolation due to Earth’s curvature.•Tropics receive more than 2.5 times of what poles receive.© 2015 Pearson Education, Inc.Figure 2.9Insolation Receipts and Earth’s Curved Surface•Subsolar point is the location where insolation is perpendicular to the surface. .© 2015 Pearson Education, Inc.Insolation at Top of Atmosphere© 2015 Pearson Education, Inc.Average Daily Net Radiation•Net Radiation = incoming shortwave Radiation − outgoing longwave radiation© 2015 Pearson Education, Inc.The Seasons •Seasonality: the seasonal variation of the Sun’s position above the horizon and changing daylengths during the year. •Annual march of the seasons •Reasons for seasons© 2015 Pearson Education, Inc.Five Reasons for Seasons 1) Revolution2) Rotation3) Tilt of Earth’s axis4) Axial parallelism5) Sphericity© 2015 Pearson Education, Inc.Reasons for Seasons 1) Revolution– Earth revolves around the sun.–Voyage takes one year.2) Rotation– Earth rotates on its axis once every 24 hours.© 2015 Pearson Education, Inc.Revolution and Rotation© 2015 Pearson Education, Inc.Reasons for Seasons 3) Tilt of Earth’s axis–Axis is tilted 23.5 degrees from plane of ecliptic .4) Axial parallelism–Axis maintains alignment during orbit around the Sun.–North pole points toward the North Star (Polaris).5) Sphericity© 2015 Pearson Education, Inc.Axial Tilt and Parallelism© 2015 Pearson Education, Inc.Annual March of the Seasons•Winter solstice—December 21 or 22–Subsolar point at southern tropic(23.5° S)•Spring equinox—March 20 or 21–Subsolar point at equator •Summer solstice—June 20 or 21–Subsolar point at Northern tropic•Fall equinox—September 22 or 23–Subsolar