The Electro-The Electro-Magnetic SpectrumMagnetic Spectrum

Light PropertiesLight PropertiesHave properties of waves…Have properties of waves…

•Crests & troughsCrests & troughs•Reflect & refract (bend)Reflect & refract (bend)

… …and particlesand particles•Can travel through spaceCan travel through space

EM WavesEM Waves The Speed of Light = cThe Speed of Light = c

= 3 x 10= 3 x 1088 m/s (1.9 miles/second) m/s (1.9 miles/second) Travels around the world about 8 times in Travels around the world about 8 times in

one secondone second

c=c= == frequency & frequency & = wavelength = wavelength

Frequency = Hertz (Hz)=1/ secondFrequency = Hertz (Hz)=1/ second Wavelength is a length – m to nmWavelength is a length – m to nm

EM SpectrumEM Spectrum Spectrum means Spectrum means ““a rangea range”” EM spectrum ranges from long EM spectrum ranges from long

wavelengths to shortwavelengths to short

Wavelength and FrequencyWavelength and Frequency

Wavelength is the distance Wavelength is the distance between two peaks (or between two peaks (or troughs)troughs)

Frequency is how frequently Frequency is how frequently the waves occurthe waves occur

A longer wavelength means a A longer wavelength means a lower frequencylower frequency

A shorter wavelength means a A shorter wavelength means a higher frequencyhigher frequency

www.nasa.gov

EnergyEnergy

As frequency As frequency decreases, energy decreases, energy increasesincreases

E = hE = h • h = 6.626 x 10h = 6.626 x 10-34-34

Joules *secondJoules *second Higher energy = Higher energy =

high frequency = high frequency = short wavelength!!short wavelength!!

Frequency

Energy

Light as a ParticleLight as a Particle Light = photonsLight = photons Photons are considered to be Photons are considered to be

both particle and a waveboth particle and a wave What does that mean?What does that mean?

• A photon is a A photon is a ““wave packetwave packet””• A photon is a A photon is a ““light particlelight particle””

The Visible SpectrumThe Visible Spectrum

violet 380-420 nm

indigo 420-450 nm

blue 450-495 nm

green 495-570 nm

yellow 570-590 nm

orange 590-620 nm

red 620-750 nm

Visible LightVisible Light Not all animals see the same Not all animals see the same

wavelengths as humanswavelengths as humans Some see shorter wavelengths Some see shorter wavelengths

(ultraviolet)(ultraviolet)• HummingbirdsHummingbirds• BeesBees

Others see longer wavelengths Others see longer wavelengths (infrared)(infrared)• BatsBats• SnakesSnakes

Visible Light vs. UVVisible Light vs. UVFlower in visible Flower in visible

lightlightFlower in UV Flower in UV

lightlight

Visible Light vs. InfraredVisible Light vs. Infrared

Bats in Bats in infrared lightinfrared light

Bats in Bats in visible lightvisible light

Full Visible SpectrumFull Visible Spectrum

Red Orange Yellow Green Blue VioletRed Orange Yellow Green Blue Violet

(Indigo)(Indigo)

What does this have What does this have to do with to do with

Astronomy??Astronomy??

Two Girls in the IRTwo Girls in the IRIs this in Is this in ““true color?true color?””

http://en.wikipedia.org/wiki/Infrared

How do we know what a How do we know what a star is made of??star is made of??

By looking at its EM spectrumBy looking at its EM spectrum The starThe star’’s s ““fingerprintfingerprint””

Hydrogen

How light or electromagnetic radiation is used in Astronomy

• Astronomers use spectroscopes• separate starlight into its colors • Identify star’s composition, temperature,

luminosity• Different wavelengths provide

different information• Temperature – Blackbody Radiation• Composition – Absorption Spectrum• Luminosity/Brightness

EmissionEmission SSppeeccttrraaFull

spectrum

Wavelengths:

H

Models of a Hydrogen Models of a Hydrogen AtomAtom

PhET's Model of a Hydrogen AtomPhET's Model of a Hydrogen Atom