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astr101_08_EMSpectrum.pdf - Astronomy 101 What is Light?...

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Astronomy 101What is Light? (EM Spectrum)APOD: 11/14/11
If you pass white light through a prism, itseparates into its component colors.ROYGB IVspectrumlong wavelengthsshort wavelengths
But visible light is only onetype of electromagneticradiation (light) emitted bystarsAstronomers are trulyinterested in the entirespectrum of Light!
Consider a Class as Seen in DifferentWavelengths of Light
Orion as Seen in Different Wavelengths of Light
But what IS light?Historical perspective, 17thcentury:Isaac Newton argued light was composed of smallparticles.Christian Huygens suggested light was a wave.19thand 20thcentury:Maxwell, Young, Einstein, and others were able toshow light behaves likeBOTHa particle and a wave!6
Thomas Youngs interference experiment
Waves of What?Maxwell showed mathematically in the 1860sthat light is a combination of electric andmagnetic fields.“EM Waves”8
Properties of a WaveA periodic wave repeats the same pattern over andover.For periodic waves:v =lfv is the wave’s speedf is the wave’s frequencylis the wave’s wavelength
In 1905 Einstein calculated the energy of a particleof light(photon)and proposed the photoelectriceffect.Ephoton= hc/l=hfe-photonh = a constantc = speed of lightl= wavelength of lightf = frequency of light
But, where does light actually comefrom?Light comes from theacceleration ofcharged particles(such as electrons andprotons)
electronAccelerating charges producelight – electromagnetic radiation!But, where does light actuallycome from?
Like the flavors of Icecream – they each provideus with differentinformation.
The Electromagnetic (EM) SpectrumEM waves of any frequency can exist.14Gamma rayshave the shortestwavelength.

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Term
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bennert
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