National Radio Astronomy Observatory Green Bank

Ewen-Purcell Horn Antenna NRAO Green Bank
Ewen-Purcell Horn Antenna NRAO Green Bank

Two views of the Ewen-Purcell Horn Antenna that was the first one to detect the 21-cm line radiation of neutral atomic Hydrogen. The horn antenna is 56 inches (142 cm) across by 43 inches (109 cm) high by a little over 127 inches (323 cm) long. The size of the horn was set by the geometric constraints of the fourth floor parapet at Lyman Lab at Harvard. The 21-cm line radiation was first detected on March 25, 1951. The horn antenna is mounted outside of the Jansky Lab at NRAO Green Bank. The plaque reads:

This horn antenna was used by Harold I. Ewen and Edward M. Purcell at the Lyman Laboratory of Physics at Harvard University in 1951 for the first detection of radio radiation from neutral atomic hydrogen in the Milky Way at a wavelength of 21 centimeters.

The next set of images are of the inside of the Anechoic Chamber.

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last updated: September 6, 2011

Author of original content: Nick Strobel