1. Earth-Sun RelationsEarth-Sun Relations
Solar Energy and the Earth as an Object inSolar Energy and the Earth as an Object in

2. OverviewOverview
 The Solar SystemThe Solar System
 FormationFormation
 StructureStructure
 Earth’s placeEarth’s place
 Solar RadiationSolar Radiation
 Electromagnetic RadiationElectromagnetic Radiation
 CompositionComposition
 SpectrumSpectrum
 InsolationInsolation
 Strength and distribution of solarStrength and distribution of solar
energy over the earthenergy over the earth
 SeasonalitySeasonality
 Result of Earth’s orientation in theResult of Earth’s orientation in the
solar system and the distribution ofsolar system and the distribution of
insolationinsolation

3. Solar SystemSolar System
 The Sun and all of itsThe Sun and all of its
orbiting bodiesorbiting bodies
 Ten planets and theirTen planets and their
satellitessatellites
 AsteroidsAsteroids
 CometsComets
 FormationFormation
 Nebular HypothesisNebular Hypothesis
(Planetesimal Hypothesis)(Planetesimal Hypothesis)
 4.6 billion years4.6 billion years
 Sun and planets coalescedSun and planets coalesced
through gravitational attractionthrough gravitational attraction
from a debris cloudfrom a debris cloud
SunSun
MercuryMercury
VenusVenus
EarthEarth
MarsMars
Asteroid BeltAsteroid Belt
(incl. Ceres)(incl. Ceres)
JupiterJupiter
SaturnSaturn
UranusUranus
NeptuneNeptune
(Pluto)(Pluto)
(Eris)(Eris)
(Haumea)(Haumea)
(Makemake)(Makemake)

4.  StructureStructure
 Ecliptic: a plane in which the bodies of the solarEcliptic: a plane in which the bodies of the solar
system revolve around the sunsystem revolve around the sun
 created by mutual gravitational pull of the planets oncreated by mutual gravitational pull of the planets on
each othereach other
 Exceptions: Mercury, Pluto, Eris, Haumea, MakemakeExceptions: Mercury, Pluto, Eris, Haumea, Makemake
 Planets move in elliptical orbitsPlanets move in elliptical orbits
 Sun at one focusSun at one focus

6.  Earth’s orientationEarth’s orientation
 Average distance to sun: 93 million milesAverage distance to sun: 93 million miles
(150 million km) which is said to equal one(150 million km) which is said to equal one
astronomical unitastronomical unit (AU).(AU).
 Perihelion: January 3Perihelion: January 3
 Aphelion: July 4Aphelion: July 4
 Earth-Moon distance: 238,866 milesEarth-Moon distance: 238,866 miles
(384,400 km)(384,400 km)
 Moon’s orbit lies in the EclipticMoon’s orbit lies in the Ecliptic
 Earth’s equatorial (rotational) plane is tiltedEarth’s equatorial (rotational) plane is tilted
23.523.5oo
from the plane of the eclipticfrom the plane of the ecliptic
 Axial ParallelismAxial Parallelism

8.  Solar radiationSolar radiation
 The Sun is a fusion reactor, and creates andThe Sun is a fusion reactor, and creates and
emits all of the chemical elementsemits all of the chemical elements
 CompositionComposition
 Electromagnetic radiationElectromagnetic radiation
 Light, in all of its formsLight, in all of its forms
 Travels at the speed of light, cTravels at the speed of light, c
 Solar WindSolar Wind
 charged particles emitted by the suncharged particles emitted by the sun
 electrons, protons, other light ionselectrons, protons, other light ions
 The earth’s magnetic field (magnetosphere) captures theseThe earth’s magnetic field (magnetosphere) captures these
particles and funnels them to the earths north and southparticles and funnels them to the earths north and south
magnetic poles, causing the Aurora Borealismagnetic poles, causing the Aurora Borealis
 Solar flares emit large amounts of these particles and causeSolar flares emit large amounts of these particles and cause
sunspotssunspots
 Heavier elements and moleculesHeavier elements and molecules

9. Electromagnetic RadiationElectromagnetic Radiation
 Light in all of its formsLight in all of its forms
 All EMR travels at the speed of light, cAll EMR travels at the speed of light, c
 c = 299,792 km/s or 186,000 miles/sc = 299,792 km/s or 186,000 miles/s
 It takes light roughly 8.333 minutes to reach earth from the sun,It takes light roughly 8.333 minutes to reach earth from the sun,
the solar system is roughly 11 hours in diameter.the solar system is roughly 11 hours in diameter.
 Types of EMR vary according to:Types of EMR vary according to:
 wavelength (wavelength (λλ))
 frequency (frequency (ff))
 c =c = λλ ff
 High frequency radiation carries more energyHigh frequency radiation carries more energy
 The classification of light according to wavelength andThe classification of light according to wavelength and
frequency yields the Electromagnetic Spectrumfrequency yields the Electromagnetic Spectrum
 Visible Light is in the mid-range of frequency and wavelengthVisible Light is in the mid-range of frequency and wavelength

11.  Composition of SunlightComposition of Sunlight
 8% Ultraviolet and shorter8% Ultraviolet and shorter
 47% Visible47% Visible
 45% Infrared and Longer45% Infrared and Longer
 The Sun emits bothThe Sun emits both
short- and long-waveshort- and long-wave
radiation due to its highradiation due to its high
temperaturetemperature
 11,00011,000oo
F (6000F (6000oo
C)C)
 The cooler Earth emitsThe cooler Earth emits
mainly long-wavemainly long-wave
radiationradiation

13. InsolationInsolation
 Intercepted Solar RadiationIntercepted Solar Radiation
 IntensityIntensity
 DistributionDistribution
 Solar ConstantSolar Constant
 The Intensity of sunlight when it reaches theThe Intensity of sunlight when it reaches the
Thermopause (upper boundary of the atmosphere)Thermopause (upper boundary of the atmosphere)
 1372 Watts per square meter1372 Watts per square meter
 Actual intensity varies across the Earth’s surfaceActual intensity varies across the Earth’s surface
 DistributionDistribution
 Intensity greatest under the subsolar pointIntensity greatest under the subsolar point
 Intensity decreases with increased latitudeIntensity decreases with increased latitude
 Intensity also varies with the seasonsIntensity also varies with the seasons

16. SeasonalitySeasonality
 An annual cycle of variation of insolation dueAn annual cycle of variation of insolation due
to a variety of factors:to a variety of factors:
 The rotational tilt of the Earth relative to theThe rotational tilt of the Earth relative to the
EclipticEcliptic
 Axial parallelismAxial parallelism
 TheThe revolutionrevolution of the Earth around the sunof the Earth around the sun
 TheThe rotationrotation of the Earth around its axisof the Earth around its axis
 Produces diurnal pattern of day and nightProduces diurnal pattern of day and night
 Circle of illuminationCircle of illumination
 Results of these factorsResults of these factors
 Subsolar point moves between 23.5Subsolar point moves between 23.5oo
N and 23.5N and 23.5oo
SS
 Changing length of day and nightChanging length of day and night

17.  Important seasonal dates:Important seasonal dates:
 June Solstice (6/21)June Solstice (6/21)
 Northern pole points toward SunNorthern pole points toward Sun
 Tropic of Cancer (23.5Tropic of Cancer (23.5oo
N) is the subsolar pointN) is the subsolar point
 Northern Summer, Southern WinterNorthern Summer, Southern Winter
 North pole gets 24 hours of sun, South gets 24 hours of nightNorth pole gets 24 hours of sun, South gets 24 hours of night
 March and September Equinox (3/21; 9/22)March and September Equinox (3/21; 9/22)
 Neither pole points toward SunNeither pole points toward Sun
 Equator is the subsolar pointEquator is the subsolar point
 Northern Spring, Southern Fall (March); Northern Fall, SouthernNorthern Spring, Southern Fall (March); Northern Fall, Southern
Spring (September)Spring (September)
 Every Place on the Earth gets 12 hours of daylightEvery Place on the Earth gets 12 hours of daylight
 December Solstice (12/21)December Solstice (12/21)
 Southern pole points toward sunSouthern pole points toward sun
 Tropic of Capricorn (23.5Tropic of Capricorn (23.5oo
S) is the subsolar pointS) is the subsolar point
 Northern Winter, Southern SummerNorthern Winter, Southern Summer
 North Pole gets 24 hours of night, South gets 24 hours of sunNorth Pole gets 24 hours of night, South gets 24 hours of sun