Astrophysics_of_Life_2

Astrophysics_of_Life_2 - Astrophysics of Life :...

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Astrophysics of Life : Astrophysics of Life : Stars Stars
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2 Wave Characteristics: Wavelength - Distance between successive wave peaks Period – Time between passing wave peaks Frequency – Number of wave peaks passing per unit time (1/Period) Wave Speed – wavelength x frequency (follow a crest ) Light Speed is 3x10 8 m/s
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3 Visible light ranges in wavelength from ~400 to ~700 nanometers. 400nm 500nm 600nm 700nm Wavelength = C O L O R
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4 Electromagnetic Spectrum Electromagnetic Spectrum communication heat detected by our eyes sunburn most energetic penetrate tissue Microwav es, cooking
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5 Blackbodies with different temperatures look like this: Hotter blackbodies are brighter and “bluer .”
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6 Wien’s Law Wien’s Law “Hotter bodies radiate more strongly at shorter wavelengths (i.e. they’re bluer ).” λ max = 0.29 cm T (K) We can measure a star’s temperature from its spectrum!
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7 (Flux) λ max = 0.29 cm T (K) Wien math fun
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8 Stefan’s Law Stefan’s Law “Hotter blackbodies are brighter overall (at every wavelength).” where: F = total radiative flux σ = constant F = σ T 4
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9 Emission Line Spectra Each element produces its own unique pattern of lines
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10 Absorption Line Spectra Spectrum of the Sun Spectrum of the Sun:
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Luminosity and Apparent Brightness Star B is more luminous, but they have the same brightness as seen from Earth.
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Apparent Brightness and Inverse Square Law Light appears fainter with increasing distance. If we increase our distance from the light source by 2, the light energy is spread out over four times the area. (area of sphere = 4 π d 2 ) Luminosity 4 π d 2 Flux = To know a star’s luminosity we must measure its apparent brightness (flux) and know its distance. Then, Luminosity = Flux *4 π d 2
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The Magnitude Scale 2 nd century BC, Hipparchus ranked all visible stars – brightest = magnitude 1 faintest = magnitude 6. To our eyes, a change of one
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This note was uploaded on 07/26/2011 for the course AST 2037 taught by Professor Eikenberry during the Fall '08 term at University of Florida.

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Astrophysics_of_Life_2 - Astrophysics of Life :...

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