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National Aeronautics and Space Administration

Goddard Space Flight Center

Astrophysics Science Division | Sciences and Exploration

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CMB Temperature vs Frequency

The intensity of a blackbody curve changes rapidly with frequency. Another way to look at the data is to convert the measured intensity at each point to the corresponding blackbody temperature. If the original intensities closely follow a blackbody curve, the corresponding temperatures will cluster around a single value, independent of frequency. The plot below shows a set of precise measurements of the temperature of the cosmic microwave background (colored points) compared to a perfect blackbody (horizontal black line). Colors indicate the measurement techniques. The data all agree with a blackbody at temperature 2.725 K, but the experimental uncertainties become large at wavelengths longer than a few centimeters.
CMB cmb_temperature vs frequency
ARCADE is a balloon-borne instrument designed to measure the CMB spectrum at centimeter wavelengths (a decade below FIRAS) to search for new signals that would be undetectably small at the shorter wavelenghts measured by FIRAS. The ARCADE frequency bands are shown in red.