Astronomy in Leiden during the occupation of World War II (1940-1945)
May 1940 the German army occupied the Netherlands. At first not too much changed. Holland was considered a related province. It was a nice summer and the economy recovered a bit after many years of severe depression. But in November 1940 there were signs of what was to come. The Jewish professors were fired. In November in Leiden professor Cleveringa (juridical department) publicly protested against the dismissal of his colleague Meijers. Next the students went on strike. The result was the closure of the university for the rest of the war years. Lectures stopped but research went on. Also the Academy of Sciences kept meeting, accepting the removal of their Jewish members.
Only during the last two years of the war, hardship for everybody became a fact of life. Because some students were persistently part of the resistance, the occupation power demanded students early 1943 to sign a declaration of loyalty to the regime. Who did not sign, was considered unemployed, and had to do forced labor in German industry. Only one quarter signed. Most of the rest went into hiding.
For the more well known professors there was another risk. Many of them were interred in a camp in St Michielsgestel, to be shot when the resistance had attacked somewhere. Minnaert, a professor in astronomy in Utrecht, was there from May 1942 until April 1944. For this reason Oort, who did not sign any loyalty document, withdrew in a cottage of his parents in law in the Eastern part of Holland. In Utrecht van de Hulst was working on his PhD. But almost till the end he was safe because on his id-card his occupation was mentioned as “assistent”. Not being a student he could appear in the open. Thus he could consult professor Léon Rosenfeld, chair theoretical physics in Utrecht, to find out which hydrogen electron jumps could produce observable microwave emission.
Even the Netherlands Astronomers Club kept convening three times a year. The last meeting was on April 15, 1944, where van de Hulst reported on the possible detectability of the 21 cm HI-line. After that it was to risky for men to travel and convene. In those days the tracking of people, and all there communications, was not a shade of what we allow to happen in these days, so hiding was possible.
Hertzsprung was not political interested and stayed on his job. Further he was a born Dane, had started his career in Postdam, and had quite some trouble fighting the pre-war Dutch authorities to stay here. The observatory was a hiding place (below the floor, the entrance at the back of the room with toilets behind the BZC), and was the printing and distribution point of the illegal journal “Trouw” (Sterrewachtlaan 2),"Trouw" 26 May 1945 had a radio (officially for time signals), and was a meeting point for illegality. He lived in the East-wing a must have been aware of what happened around him. In general the astronomical community in general tried to reconcile political differences. Thus no strong viewpoints were made public towards governments where observatoria were located in South Africa, Greece, Chili and Spain.
Observations went on as long as supplies allowed. But at the end of 1944 little was left, although the observatory was not stripped clean, like the Kamerlingh Onnes Laboratory early in the war.
As far as research went on it was mainly concerning things which only needed paper and pen. E.g. many monographs, reviews and textbooks appeared shortly after the war.First yearly report after the war
Hier een interview met H. Kleibrink. Gehouden door P.J. van der Burgh op 29 maart 1982. Getypt, 5 bladzijden.interviewkleibrink1982.pdf Herman Kleibrink (1910) geniet vooral bekendheid wegens zijn foto’s die hij tijdens de bezetting en de bevrijding heeft gemaakt. Ook heeft hij filmopnamen gemaakt van de bevrijding en van geïnterneerde politieke delinquenten. Kleibrink werkte tijdens de bezetting als technicus bij de Sterrenwacht. Daar ontstond een groepje mensen, dat het illegale blad Trouw ging verspreiden. Geleidelijk aan wordt steeds vaker gebruik gemaakt van zijn deskundigheid om radio’s te onderhouden en fotografie.