Radiation Basics
.1
1
10
100
Wavelength (micrometers)
FIGURE 10.4. Emittance spectra for 6000 K and 288 K blackbody sources
approximating.emission from the sun and the earth.
Eq. (10.5) with respect to A, setting the result to zero, and solving for
temperature. The result is called Wien's law:
where h, is in micrometers. The wavelengths for peak emittance for the
6000 K and 288 K sources in Fig. 10.4 are 0.48 and 10 pm respectively.
10.7 Spectral Distribution of Solar and Thermal
Radiation
The actual extraterrestrial solar spectrum is shown in Fig. 10.5. Here it
is plotted using a linear wavelength scale. It has nearly the same shape
as a blackbody source at 6000 K, and the wavelength at peak emission
is between blue and green, as expected from the Wien's law calculation. As solar radiation passes through the atmosphere of the earth,
some wavelengths are almost completely absorbed. The ozone layer in
the stratosphere absorbs much of the ultraviolet radiation. Water
vapor is the main absorber in the infrared.
The strong absorption of short wavelength ultraviolet radiation by
ozone is of particular importance to living organisms. Referring to Fig.
10.1, it can be seen that radiation at these wavelengths can cause skin
cancer. It is actually capable of inducing mutation in any genetic material
and of germicidal action. This is the reason for the recent concern over
destruction of the ozone layer by release into the atmosphere of chlo-
.1
1
10
100
Wavelength (micrometers)
FIGURE 10.4. Emittance spectra for 6000 K and 288 K blackbody sources
approximating.emission from the sun and the earth.
Eq. (10.5) with respect to A, setting the result to zero, and solving for
temperature. The result is called Wien's law:
where h, is in micrometers. The wavelengths for peak emittance for the
6000 K and 288 K sources in Fig. 10.4 are 0.48 and 10 pm respectively.
10.7 Spectral Distribution of Solar and Thermal
Radiation
The actual extraterrestrial solar spectrum is shown in Fig. 10.5. Here it
is plotted using a linear wavelength scale. It has nearly the same shape
as a blackbody source at 6000 K, and the wavelength at peak emission
is between blue and green, as expected from the Wien's law calculation. As solar radiation passes through the atmosphere of the earth,
some wavelengths are almost completely absorbed. The ozone layer in
the stratosphere absorbs much of the ultraviolet radiation. Water
vapor is the main absorber in the infrared.
The strong absorption of short wavelength ultraviolet radiation by
ozone is of particular importance to living organisms. Referring to Fig.
10.1, it can be seen that radiation at these wavelengths can cause skin
cancer. It is actually capable of inducing mutation in any genetic material
and of germicidal action. This is the reason for the recent concern over
destruction of the ozone layer by release into the atmosphere of chlo-