Radiation and Spectroscopy

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Ami Walters
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1 The Nature of Light and Atoms

2 Announcements Second homework is due a week from today Preceptor-led study group Mondays 10:30AM-12:00noon Room 330 Kuiper Space Sciences (this is the room just behind the slots where assignments are handed back and early homework is handed in) Thursday s reading assignment Sections 6-1, 6-2, 6-3, 6-7 (pp , pp )

3 Today s topics Speed of light Light s wave-like properties Concept of a Spectrum The electromagnetic spectrum Wien s law Stefan-Boltzmann law Light s particle-like properties

4 Why is studying Light important to Planetary Scientists? Spectroscopy! Shape of spectrum Temperature Lines in spectrum Composition Imaging at a variety of wavelengths

5 The speed of light Galileo s experiments (early 1600 s) Inconclusive Romer s observations (1675) Demonstrated that light moves at a finite speed Fizeau-Foucault method (1850) Rotating mirror Very close to the correct answer

different than those predicted and depended on the relative position

6 Romer s Observations Meticulous observations of the eclipses of Jupiter s moons He found that the observed eclipse times were different than those predicted and depended on the relative position of Jupiter and the Earth Attributed this to being due to the finite speed of light

$which it is moving The refractive index of$ a medium is the speed of light in a vacuum,

$For instance, water has a refractive index$

7 The Speed of Light depends on the medium in which it is moving The refractive index of a medium is the speed of light in a vacuum, divided by the speed of light in the medium For instance, water has a refractive index of about 1.3 (depending on the wavelength)

8 Traveling disturbance Energy moves a long way, but the carrier doesn t Characterized by: Wavelength: Distance between crests Amplitude:Height of crest Frequency: Number of crests per second Velocity: Speed and direction of the wave Waves Speed of a wave is the wavelength times the frequency v = λ ω (v = speed, λ = wavelength, ω = frequency )

$Changing Waves Interference Interference Waves add when they collide Can be constructive or destructive Diffraction Waves bend going$

9 Changing Waves Interference Interference Waves add when they collide Can be constructive or destructive Diffraction Waves bend going around corners Doppler Effect Waves compress or expanded due to moving source Useful to determine speed of wave emitters Diffraction

10 Young s double-slit experiment This famous experiment convincingly demonstrated the wave-like property of light

11 Newton s Experiment Showed convincingly that Light is a SPECTRUM

12 Electromagnetic Spectrum Light has many frequencies and wavelengths But all move at the same speed in a vacuum Blue light has a shorter wavelength than Red light

13 Why is it called the Electromagnetic Spectrum? Because Electric and Magnetic Fields are what is waving in light

14 Imaging Solar System Bodies at Different Wavelengths Uranus Sun Visible Near IR Xrays

15 False color images: Cassini/VIMS scientists created these images by mapping 3 separate IR wavelengths into Red,Green,Blue to get this image of Titan

16 Doppler Effect

17 The Doppler Effect is useful for astronomers because it tells whether an object is moving towards or away from the observer Useful for determining the rotations of planets whose surface features are hard to see Venus, Titan, Mercury Doppler Image of the Sun

18 Doppler Shift Equation Δ = change Δλ = λ λ 0 = wavelength change λ 0 = wavelength of stationary source v = speed of emitter c = speed of light

Light - electromagnetic radiation

Light - electromagnetic radiation Astronomy & Light Astronomy is a science In science we know by doing experiments When multiple experiments give the same results we develop theories and laws In astronomy many of the experiments are done