Calibration-Horn-1967

The Calibration Horn Antenna, nicknamed the “Little Big Horn,” at Green Bank in 1967. As its name implies, this 120-foot long horn antenna was used to measure the intensity of radio waves coming from the sky’s strongest non-solar radio source, Cassiopeia A. The Calibration Horn measured a total power output for Cas A at a frequency of 1.4 GHz (a wavelength of 20cm), and thus provided astronomers with a standard reference point on the sky against which they could measure other sources.

Credit: NRAO/AUI/NSF
Source: public.nrao.edu/gallery/little-big-horn