Observational Aspects of the Microwave Cosmic Background Spectrum
The discovery of the isotropic microwave background, in 1964, was followed by a decade of careful measurements of the background flux throughout the centimetric and millimetric ranges of wavelength. The results of these measurements are not inconsistent with a Planckian spectrum but the absolute precision of the measurements is not as high as is frequently assumed. More recently attention has turned to searches for variations in the flux density with direction in the sky, while preparations are made in laboratories around the world for a second wave of measurements of the spectrum which are to have a much higher absolute precision. I point out in this article the limitations in our present knowledge of the microwave background, identify the observational difficulties in improving that knowledge and report on some of the plans for future measurements. The excellent recent critical review of background measurements by R.J. Weiss (1980) and the papers presented at a 1979 Copenhagen Symposium (Kalchar et.al. 1979) should be consulted for further detail.
KeywordsLiquid Helium Thermal Emission Signal Beam Antenna Pattern Horn Antenna
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