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| Background Radiation |
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| In astronomy, the low temperature microwave radiation that arrives at the earth's surface from all directions of outer space is called background radiation. It is so named because it forms a background to all the radio sources that have been detected by radio telescopes. Cosmic background radiation was predicted to exist as part of the Big Bang theory of the origin of the universe. According to this theory such radiation is the lingering remains of the extremely hot conditions that prevailed in the first moment of the Big Bang. |
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| A number of sources other than the cosmic radiation from the space contribute to the background radiation. |
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| These may be: |
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 Radiation from the sun |
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 Rocks in the earth which contain traces of radioactive substances |
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 Naturally occurring radioisotopes. |
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 Artificial radioisotopes. |
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 Products made from nuclear explosions, e.g., strontium - 90 which has a half-life of 28 years. |
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