Plaque next to Ewen-Purcell Horn Antenna now at <a href="https://en.wikipedia.org/wiki/National_Radio_Astronomy_Observatory" class="extiw" title="w:National Radio Astronomy Observatory">National Radio Astronomy Observatory</a> in <a href="https://en.wikipedia.org/wiki/Green_Bank,_West_Virginia" class="extiw" title="w:Green Bank, West Virginia">Green Bank, West Virginia</a>. Text of Plaque: <i> This Horn antenna was used by Harold L. Ewen and <a href="https://en.wikipedia.org/wiki/Edward_M._Purcell" class="extiw" title="w:Edward M. Purcell">Edward M. Purcell</a> at the Lyman Laboratory of Physics at Harvard University in 1951 for the first detection of radio radiation from nuclear atomic hydrogen gas in the milky way at a wavelength of 21 centimeters.</i>
<a href="//commons.wikimedia.org/wiki/User:Jarekt" title="User:Jarekt">Jarek Tuszyński</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>