1. 2 phys 181-701 astronomy 3 may the warp be the white light of morning, may the weft be the red...
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Phys 181-701Phys 181-701AstronomyAstronomy
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May the warp be the white light of morning,May the weft be the red light of evening,May the fringes be the falling of the rain,May the border be the standing rainbow.Thus weave for us a garment of brightness.
Song of the Sky Loom (Native American Traditional)
Garment of Brightness
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IntroThe Interaction of Matter and
Electromagnetic Radiation(Light)
Understanding This is an Important Tool of Astronomy
Light Interacts with matter in several ways…
•Reflection•Refraction•Diffraction•Absorption•Emission•Gravitation!
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Review
•Light is a form of Electromagnetic Radiation
•Radiation may be described as waves
•Waves are described by their frequency, wavelength, amplitude and speed.
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Time period of mars
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Reflection
Reflection Nebulae
Reflection
Light simply scatters off the dust and gas…
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RefractionRefraction
Light bends when moving from one substance to another…
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Diffraction
Light bends around obstacles…
Diffraction
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Absorption&EmissionAbsorption and Emission
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Observations
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Thermal Radiation
Thermal (Blackbody) Radiation Spectra
273 Kelvin = 0 ºC
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1. Stefan-Boltzmann Law: Hotter objects emit more power per unit area.
2. Wien’s Law: Hotter objects emit light that has a higher average energy.
Two Law
s
Two Laws of Thermal Radiation:
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Practical ExampleChange in Brightness
Change in Color
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Calculation Example
Example:
Consider a perfect thermal emitter with a temperature of 15000 K. How much power does it emit per unit area? What is the wavelength of maximum intensity?
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Putting it Together
Putting it Together…
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Analysis
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Doppler Shift
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Shifted Spectra
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Doppler Effect Formula:
Doppler Formula
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Why does the sun shine?
•Chemical Burning – insufficient radiation
•Radiative Cooling – only thousands of years
•Gravitational Contraction – only 25 million years
Why does the sun shine?
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Stars convert energy into matter.
E=mc^2
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600 million tons of H -> 598 million tons of He
IN ONE SECOND
Proton-Proton Chain
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Basic Solar Structure
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The force of gravity inward and the radiation pressure outward balance each other out.
Gravitational Equilibrium
Radiation Pressure
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91.2% Hydrogen – 8.7% Helium
0.1% Heavier Elements
SpectroscopyVisible Spectrum
Spectroscopy
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Luminosity
Luminosity
The total power output of the sun: 3.8x1024 watts!!!
Think of your 60 watt light bulb.
1 second of the earth luminosity contains enough energy tomeet our needs for roughly 500,000 years!
Only about one two-billionth of that reaches Earth.
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Sun Spots
Sun Spots
Not at all dark
Roughly the size of the earth
Show the differences in rotation: 27 days equator – 31 days poles
Only about one two-billionth of that reaches Earth.
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Granularity
Granularity of the Solar Surface
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Convection
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A Solar Prominence
Prominence
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Solar Flare
Flare
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Understanding the sun:
simulations
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IMPORTANT
• Light Interacts with Matter• Spectrum ( Energy - Temp -
Color )• E and A Spectra• Radiation Laws• Doppler Shift• Gravitational Equilibrium
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Next Time……
STARS,STARS, A Mass ofA Mass of
Incandescent GasIncandescent Gas
END