Earth-Sun RelationsEarth-Sun Relations

Solar Energy and the Earth as an Object in Solar Energy and the Earth as an Object in SpaceSpace

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 solar Strength and distribution of solar

energy over the earthenergy over the earth SeasonalitySeasonality

Result of Earth’s orientation in Result of Earth’s orientation in the solar system and the the solar system and the distribution of insolationdistribution of insolation

Solar SystemSolar System The Sun and all of its The Sun and all of its

orbiting bodiesorbiting bodies Ten planets and their Ten planets and their

satellitessatellites AsteroidsAsteroids CometsComets

FormationFormation Nebular Hypothesis Nebular Hypothesis

(Planetesimal Hypothesis)(Planetesimal Hypothesis) 4.6 billion years4.6 billion years Sun and planets coalesced Sun and planets coalesced

through gravitational through gravitational attraction from a debris attraction from a debris cloudcloud

SunSunMercuryMercuryVenusVenusEarthEarthMarsMarsAsteroid Belt Asteroid Belt

(incl. Ceres)(incl. Ceres)JupiterJupiterSaturnSaturnUranusUranusNeptuneNeptune(Pluto)(Pluto)(Eris)(Eris)(Haumea)(Haumea)(Makemake)(Makemake)

StructureStructure Ecliptic: a plane in which the bodies of the Ecliptic: a plane in which the bodies of the

solar system revolve around the sunsolar system revolve around the sun created by mutual gravitational pull of the created by mutual gravitational pull of the

planets on each otherplanets on each other Exceptions: Mercury, Pluto, Eris, Haumea, Exceptions: Mercury, Pluto, Eris, Haumea,

MakemakeMakemake Planets move in elliptical orbitsPlanets move in elliptical orbits

Sun at one focusSun at one focus

Earth’s orientationEarth’s orientation Average distance to sun: 93 million Average distance to sun: 93 million

miles (150 million km) which is said to miles (150 million km) which is said to equal one equal one astronomical unitastronomical unit (AU). (AU).

Perihelion: January 3Perihelion: January 3 Aphelion: July 4Aphelion: July 4

Earth-Moon distance: 238,866 miles Earth-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 Earth’s equatorial (rotational) plane is

tilted 23.5tilted 23.5oo from the plane of the from the plane of the eclipticecliptic

Axial ParallelismAxial Parallelism

Solar radiationSolar radiation The Sun is a fusion reactor, and creates and The 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 The earth’s magnetic field (magnetosphere) captures

these particles and funnels them to the earths north these particles and funnels them to the earths north and south magnetic poles, causing the Aurora Borealisand south magnetic poles, causing the Aurora Borealis

Solar flares emit large amounts of these particles and Solar flares emit large amounts of these particles and cause sunspotscause sunspots

Heavier elements and moleculesHeavier elements and molecules

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 It takes light roughly 8.333 minutes to reach earth from

the sun, the solar system is roughly 11 hours in diameter.the sun, the solar system is roughly 11 hours in diameter. Types of EMR vary according to:Types of EMR vary according to:

wavelength (wavelength ()) frequency (frequency (ff)) c = c = f f High frequency radiation carries more energyHigh frequency radiation carries more energy

The classification of light according to wavelength The classification of light according to wavelength and frequency yields the Electromagnetic and frequency yields the Electromagnetic SpectrumSpectrum

Visible Light is in the mid-range of frequency and Visible Light is in the mid-range of frequency and wavelengthwavelength

Composition of SunlightComposition of Sunlight 8% Ultraviolet and 8% Ultraviolet and

shortershorter 47% Visible47% Visible 45% Infrared and Longer45% Infrared and Longer

The Sun emits both The Sun emits both short- and long-wave short- and long-wave radiation due to its high radiation due to its high temperaturetemperature 11,00011,000ooF (6000F (6000ooC)C)

The cooler Earth emits The cooler Earth emits mainly long-wave mainly long-wave radiationradiation

InsolationInsolation Intercepted Solar RadiationIntercepted Solar Radiation

IntensityIntensity DistributionDistribution

Solar ConstantSolar Constant The Intensity of sunlight when it reaches the The Intensity of sunlight when it reaches the

Thermopause (upper boundary of the Thermopause (upper boundary of the atmosphere)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

SeasonalitySeasonality An annual cycle of variation of insolation An annual cycle of variation of insolation

due to a variety of factors:due to a variety of factors: The rotational tilt of the Earth relative to the The rotational tilt of the Earth relative to the

EclipticEcliptic Axial parallelismAxial parallelism The The revolutionrevolution of the Earth around the sun of the Earth around the sun The The rotationrotation of the Earth around its axis of 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 23.5ooN and N and

23.523.5ooSS Changing length of day and nightChanging length of day and night

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 (23.5ooN) 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 North pole gets 24 hours of sun, South gets 24 hours of

nightnight 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, Northern Spring, Southern Fall (March); Northern Fall,

Southern Spring (September)Southern 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 (23.5ooS) 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 North Pole gets 24 hours of night, South gets 24 hours of

sunsun