Page 93 - Intro to Space Sciences Spacecraft Applications

80 Zntroduction to Space Sciences and Spacecraft Applications
wavelength

Figure 4-2. Electromagnetic wave. A simple sine-wave depicts some of the
characteristics of an electromagnetic wave.

tionship between frequency and wavelength is given in equation 4-1 in
which c represents the speed of light (3 x lo8 dsec in a vacuum).

C
f = - cycles per sec ond (Hz) (4-1)
h
Two other characteristics of electromagnetic radiation, which we will
look at more closely later, are the amplitude and the phase. Amplitude is
represented by the height of the peaks of the sine-wave, and phase
describes a particular location along the wave.
Figure 4-3 shows many of the regions of the electromagnetic spectrum
with which we will be dealing. Notice how small the range of visible
wavelengths is. Remember that as the frequency increases, the wave-
length decreases, as explained by equation 4-1.

Blackbody Radiation. A blackbody is a theoretical body which has the
properties of being a perfect radiator (and absorber) of energy. As we will
see in the next few sections, the characteristics of the energy radiated by
a blackbody is a function of the body’s temperature. Though it is a theo-
retical concept, many bodies resemble blackbodies, at least closely or over
a particular range of wavelengths, and can be approximated by blackbody
relationships.

Stefan-Boltvnann Law. In 1879 an Austrian physicist, Josef Stefan, with
help from his contemporary Ludwig Boltzmann, demonstrated that the
total energy radiated by a blackbody increased as a function of the fourth