The Electromagnetic Spectrum

Figure 1.1: The Electromagnetic Spectrum

The Figure 1.1 plots the electromagnetic spectrum in terms of the amount of transmission through the earth's atmosphere as a function of the wavelength. In the figure, shaded areas show the amount of opacity of the atmosphere at certain wavelengths, whereas, clear areas show the transparency of the atmosphere at other wavelengths. As can be seen, there are two prominent bands or windows, corresponding to the optical and radio wavelengths, through which one can make observations from the surface of the earth. The radio window covers a much larger wavelength band than the optical window in the electromagnetic spectrum. Depending on the atmospheric conditions the width of the radio window may vary, but is in general from $\sim$ 1 cm to $\sim$10 m.