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Incoming links: Observational cosmology
Cosmic microwave background Created 2026-09-28 Updated 2026-10-18
The cosmic microwave background is nearly isotropic thermal electromagnetic radiation. Its spectrum connects radio receiver measurements with the universe's thermal history: redshift preservation of a thermal photon spectrum cools a blackbody spectrum as space expands. The 1965 Princeton analysis described this relation.[ref]
Cosmic Black-Body Radiation by R. H. Dicke and others. pp.415–416: expansion cools radiation while preserving a thermal spectrum
A radiometer cannot label a received photon as cosmic, atmospheric or instrumental. Its measured power combines the incoming radiation with the receiver response. The useful question is which comparisons and controls can isolate a sky contribution. This makes the Penzias-Wilson microwave background experiment an example of both observational cosmology and measurement calibration.