Waldmeier developed his career at the Swiss Federal Observatory in Zurich. In 1939 he initiated the construction of a high-altitude astrophysical station above Arosa to enable routine coronagraphic observations of the solar corona. The facility operated as an external station of the ETH observatory for solar research through 1980.[4][5] He was appointed professor of astronomy at ETH Zurich in 1945 and served concurrently as director of the Swiss Federal Observatory until 1979. He also held a professorship at the University of Zurich, where he advanced from extraordinary to ordinary professor by the mid 1950s.[1][6]
As director he restarted the Quarterly Bulletin on Solar Activity in 1947 and expanded Zurich's international network for sunspot reports.[7] He built a solar tower in Zurich in 1951 and in 1957 established the Specola Solare Ticinese in Locarno as an external observing station to improve continuity of the sunspot record under complementary weather conditions south of the Alps.[7][8][9] Under his leadership the Zurich program continued the production of the relative sunspot number. In 1947 he introduced a weighted counting method that assigned greater weight to larger spots, a change later analyzed in the literature on sunspot number calibration.[10][11]
Waldmeier also organized the first postwar General Assembly of the International Astronomical Union in Zurich in 1948. He presided over solar physics activities within the IAU and led numerous eclipse expeditions dedicated to coronal photography.[6][12] His monograph "The Sunspot-Activity in the Years 1610-1960" summarized the Zurich series and helped standardize usage of the sunspot number in space weather and climate studies.[13]
Waldmeier retired in 1979. ETH Zurich dissolved the Swiss Federal Observatory in connection with his retirement, and the responsibility for the continuous sunspot number series moved in 1980 to the Royal Observatory of Belgium in Brussels, where the program continued as the International Sunspot Number with Specola Solare Locarno serving as pilot station.[2][14]
As director of the Zurich Observatory until 1980, Waldmeier insisted on counting sunspots by eye over automated methods, using a Fraunhofer refracting telescope installed by Zurich Observatory director Rudolf Wolf in 1849.[15]
He suffered a debilitating stroke in 1986 and died in 2000.[2]
