The Electro-Magnetic Spectrum

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The Electro-Magnetic Spectrum
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Light Properties

• Have properties of waves
• Crests troughs
• Reflect refract (bend)
• and particles
• Can travel through space

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EM Waves

• The Speed of Light c
• 3 x 108 m/s (1.9 miles/second)
• Travels around the world about 8 times in one
  second
• c??
• ? frequency ? wavelength
• Frequency Hertz (Hz)1/ second
• Wavelength is a length m to nm

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EM Spectrum

• Spectrum means a range
• EM spectrum ranges from long wavelengths to short

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Wavelength and Frequency

• Wavelength is the distance between two peaks (or
  troughs)
• Frequency is how frequently the waves occur
• A longer wavelength means a lower frequency
• A shorter wavelength means a higher frequency

www.nasa.gov
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Energy
Frequency

• As frequency decreases, energy increases
• E h?
• h 6.626 x 10-34 Joules second
• Higher energy high frequency short
  wavelength!!

Energy
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Light as a Particle

• Light photons
• Photons are considered to be both particle and a
  wave
• What does that mean?
• A photon is a wave packet
• A photon is a light particle

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The Visible Spectrum
red 620-750 nm
orange 590-620 nm
yellow 570-590 nm
green 495-570 nm
blue 450-495 nm
indigo 420-450 nm
violet 380-420 nm
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Visible Light

• Not all animals see the same wavelengths as
  humans
• Some see shorter wavelengths (ultraviolet)
• Hummingbirds
• Bees
• Others see longer wavelengths (infrared)
• Bats
• Snakes

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Visible Light vs. UV

• Flower in visible light

Flower in UV light
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Visible Light vs. Infrared
Bats in visible light

• Bats in infrared light

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Full Visible Spectrum

• Red Orange Yellow Green Blue Violet
• (Indigo)

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What does this have to do with Astronomy??
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Two Girls in the IR

• Is this in true color?

http//en.wikipedia.org/wiki/Infrared
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How do we know what a star is made of??

• By looking at its EM spectrum
• The stars fingerprint

Hydrogen
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How light or electromagnetic radiation is used in
Astronomy

• Astronomers use spectroscopes
• separate starlight into its colors
• Identify stars composition, temperature,
  luminosity
• Different wavelengths provide different
  information
• Temperature Blackbody Radiation
• Composition Absorption Spectrum
• Luminosity/Brightness

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Emission Spectra
Full spectrum
Wavelengths
H
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Models of a Hydrogen Atom

• PhET's Model of a Hydrogen Atom

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