Radiation Curves

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

Changes with Temperature

*

Visible

5000 K

6000 K

7000 K

*

*

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

Total Energy

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

ORION

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

Two-Dimensional Spectra

Continuous

Emission

Absorption

Visible Light Infrared Light

The Orion Nebula