April 18: Max Waldmeier

Max Waldmeier

April 18, 1912 - September 26, 2000

Max Waldmeier was one of the leading personalities in solar physics of the 20th century.

He graduated from ETH Zurich in 1935 at the age of 23 and got his PhD there two years later on a thesis about the laws that govern the sunspot activity. He was professor at ETH Zurich and at the University of Zurich during 34 years, 1945 - 1979. During these years he also served as Director of the Eidgenössische Sternwarte (Swiss Federal Observatory) in Zurich. In 1948 he organized in Zurich the first General Assembly of the International Astronomical Union that took place after World War II. He served as a member of the Editorial Board of Solar Physics from 1968 to 1977.

Waldmeier founded the Astrophysical Observatory Arosa in 1939, a mountain station where he could carry out his observations of the Sun's corona. This was one of the first coronagraphic stations since Lyot's invention of the coronagraph. In 1951 he built a solar tower telescope in Zurich and in 1957 the Specola Solare in Locarno, a solar station on the southern side of the Alps, where the weather is usually complementary to that in Zurich. He carried out more than 20 expeditions to study the corona at solar eclipses. 

The Swiss Federal Observatory under the direction of Waldmeier served as the World data Center for Sunspots and was responsible for the IAU publication Quarterly Bulletin on Solar Activity. More than 30 observatories around the world sent their sunspot observations to Zurich, where they were reduced together with the Swiss observations (in Zurich and Locarno) to form the Zurich Sunspot Number, carefully calibrated to a common scale. This continuous record of relative sunspot numbers was initiated in 1855 by the first Director of the Swiss Federal Observatory, Rudolf Wolf.

Waldmeier's systematic observations of various aspects of solar activity, from the photosphere to the corona, spanned several decades and have provided the foundation for much of our current knowledge about the Sun's activity cycle. Much of what we take for granted today can actually be traced back to pioneering work by Waldmeier.