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Continuous Radiation
• How bright is the continuous spectrum at different colors?
• How does a perfect light source emit its light?
400nm 500nm 600nm 700nm
Early Experiments
Darken inside with carbon black
Measure radiation that emerges from hole
Blackbody Radiation
Blackbody Radiation
0.00.51.01.52.02.53.03.54.0
0 500 1000 1500
Wavelength (nm)
Re
lativ
e E
nerg
y
Vis
IRUV
Wien’s Displacement Law
• The wavelength of the peak of the blackbody curve is inversely proportional to the temperature.
T
1max
Cool stars are red - hot stars are blue
Wilhelm Wien
Stefan-Boltzmann Law
• Area under the blackbody curve measures the total energy output of the source and is proportional to T4.
4TE Josef Stefan
Ludwig Boltzmann
Blackbody Radiation• Everything in nature emits light• The type of light emitted depends
on the temperature of the sourceThe walls of this room
• IR
Stars• Visible and UV
The Corona of the Sun (2,000,000 K)• X-rays
Some Real Stars
0.0
0.5
1.0
1.5
2.0
2.5
0 500 1000
Wavelength (nm)
Re
lativ
e E
nerg
yRigel 11500 K
Sirius A 10000 K
The Sun 5800 K
More Real Stars
0.000.010.020.030.040.050.060.070.08
0 500 1000
Wavelength (nm)
Re
lativ
e E
nerg
y The Sun
5800 KCapell
a 5200
K
Betelgeuse 3600 K
Review
• Animation
Visible Light Infrared Light
The Orion Nebula