The atmosphere of the earth protects us
from many harmful types of radiation but it is also most important that it is transparent
to ranges of wavelengths which are in sue by astronomers to study the Universe.
Two such regions are the visible region of the spectrum and the radio or microwave
area.
The optical window extends from around 3x10-6 m to about
10-7 m while the radio window is transparent to radiation with wavelengths
between 1 cm and 10 m.
The fact that the atmosphere is only transparent
to relatively small bands of wavelength limits the study of the Universe. Since all
wavelengths below the visible are effectively blocked X ray and gamma ray
astronomy have only been possible in the last forty years. The study of astronomical
X ray sources is done from detectors placed in satellites in orbit around the
Earth.
(The diagram above has been
simplified).