Tootfinder

75 years ago #OTD the #interstellar #hydrogen line at 21 cm was detected for the first time in Europe (https://sci-hub.vg/10.1038/168357a0), following the first-ever detection - in the U.S. - in March 1951 (https://sci-hub.vg/10.1038/168356a0): see https://www.astron.nl/may-11-75-years-of-the-hydrogen-line-in-the-netherlands-from-kootwijk-to-westerbork-and-ska/ for what followed.