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									                                                         The rise of radio astronomy in the Netherlands: a peculiar history
                                                                                                    Astrid Elbers
                                                                                Leiden Observatory, Leiden University, The Netherlands

Introduction                                                              The 21-cm hydrogen line                                                    Dwingeloo and Westerbork                                                  Conclusions
The postwar take-off of Dutch radio astronomy had a special character     At a clandestine meeting of the Nederlandse Astronomenclub (NAC)           In the years of the Kootwijk observations, Oort kept pursuing his plans   By 1970, radio astronomy was firmly established as a (sub)discipline
in several respects. In Australia, England and the USA, radio-            (Dutch Astronomers Club) on April 15th 1944 at Leiden Observatory,         for a much bigger and more sensitive telescope.The successful             in the Netherlands. The reasons for this are multiple and need to be
astronomical research was initiated in 1945 by radio engineers and        van de Hulst could confirm that a spectral line of hydrogen existed at     observations in Kootwijk quickly caused ZWO to approve the plans          further explored. Certainly, the role of the Leiden astronomer Jan
physicists who had acquired extensive experience with radio receivers     21 cm.                                                                     for a new radio telescope, with a 25-m dish. They provided financial      Hendrik Oort was crucial in this respect. Besides being a great
during World War Two. In the Netherlands, such experience was                  Only a few days after van de Hulst’s talk at the NAC, Oort asked      support for its design and construction. The telescope was built in       scientist, he excelled in efficient planning and lobby work.
lacking. Moreover, the war had brought Dutch science to a grinding        dr. C.J. Bakker of Philips factories to construct a receiver for a radio   Dwingeloo and inaugurated in April 1956. For a full year, it would be           The contacts Oort established with Bok were fruitful for the
halt. In spite of these unfavourable conditions, the Netherlands would    telescope with a mirror of 10 to 20 metres. The mirror could be built      the largest telescope in the world.                                       relations between the Netherlands and the US. And the fact that Oort
rapidly emerge as a centre for radio astronomy. My aim is to account      by the mechanical workshop of the Leiden Observatory. Bakker                                                                                         was a personal friend of Bannier, the president of ZWO, was also an
for this unlikely success. The initiative did not come from engineers     replied this certainly would be possible after the war. At this moment,                                                                              advantage. Above all, Bannier was a physicist with a great interest in
and physicists, but from leading individuals at classical astronomical    cooperation with the industry was a fact.                                                                                                            astronomy.
research, especially Jan Hendrik Oort at Leiden.                               Shortly after the war, Oort applied to the Department of Science                                                  Figure 5. The Dwingeloo             Oort managed to recruit important allies in industry and
                                                                          and Education for funding for his telescope. But since the                                                             telescope                     government. The question is why all these parties were willing to
                                                                                                                                                                                                 With this telecope – which
                            Lacking      money,     instruments,   and    cost was much too high, he didn’t get what he asked for.                                                                                             cooperate in this project and what they had to gain from it.
                                                                                                                                                                                                 could make much more
                            expertise, a large part of the success of                                                                                                                            detailed observations than          Last but not least, we need to consider the more structural
                            Dutch radio astronomy was due to his                                                                                                                                 the Kootwijk one – several    circumstances that made it possible that the initiatives of Oort turned
                                                                                                                                                                                                 projects were undertaken.     out to be successful.
                            recruiting of several allies both in
                            astronomical and physical communities as
                                                                          Kootwijk                                                                                                               Among them are the
                                                                                                                                                                                                 galactic and extragalactic
                            well as in industry and government circles.   The Dutch PTT (Post,                                                                                                   research of hydrogen (for
                                                                          Telephone            and                                                                                               example of the Andromeda
                                                                          Telegraph)      however,                                                                                               Nebula)
                            Figure 1. Professor Jan Hendrik Oort of       gave Oort access to a                                                      observations than the
                            Leiden Observatory                                                                                                           Kootwijk one – several
                                                                          German radar reflector
                                                                          at     its          tele-
                                                                                                                                                                                                                               Archives and Literature
                                                                                                                                                                                                                               Oort archive, Leiden University
                                                                          communication station
                                                                          in Kootwijk and Philips                                                                                                                              Casimir, H.B.G., Voorzieningen ten behoeve van de research binnen de faculteiten
                                                                          provided a receiver for                                                                                                                                  der wis- en natuurkunde der Nederlandse universiteiten, ’s-Gravenhage, 1959.
                                                                          21-cm wavelength in                                                        During the ‘Dwingeloo period’, the Netherlands had recovered from         Raimond, E., Historical notes: Four decades of Dutch radio astronomy, twenty-five
                                                                          1948.       Oort also                                                                                                                                    years of Westerbork telescope, in: Raimond, E. and Genee, R. eds., The
                                                                                                                                                     the war and a period of extensive economic growth began. The                  Westerbork Observatory; Continuing Adventures in Radio Astronomy,
                                                                          managed to obtain a                    Figure 3. The Kootwijk telescope    universities benefited from this. In the late 1950’s, there was for           (Astrophysics and Space Science Library, 207), Dordrecht, Boston and London,
                                                                          funding from the ZWO                                                       instance a considerable increase in the budget of the ZWO. However,           1996, pp.11-51.
                                                                          (Netherlands Organisation for the Advancement of Pure Research). It        despite the economic growth till 1975, it has sometimes been              Spoelstra, T.A.Th. ed., Een zilveren spiegel. 25 jaar Radiosterrenwacht Dwingeloo.
Communication in wartime                                                  was a lucky coincidence that the director of ZWO, J.H. Bannier, a          suggested that Dutch natural scientific research was not very                 17 april 1956 – 17 april 1981, Dwingeloo, 1981.
Just before World War Two, the American electronic engineer Grote         physicist and friend of Oort’s, had a great interest in astronomy.         innovative. It adopted and elaborated issues that had already started     Van Berkel, K., Kwaliteit en zuinigheid in het wetenschappelijk onderwijs, in:
                                                                                                                                                                                                                                   Schuyt, K. and Taverne, E. eds., 1950: Welvaart in zwart-wit (Nederlandse
Reber from Wheaton built a radio telescope in his garden with which                                                                                  elsewhere, but did not come up with truly new things.                         cultuur in Europese context. Deel 4) Den Haag, 2000, pp. 331 – 354.
he made the first maps of radio emission of the Galaxy. He published      For the radio astronomical project, a foundation was erected in 1949,          A big exception in that picture was Dutch astronomy. With radio       Van Woerden, H. and Strom, R.G., The Beginnings of Radio Astronomy in the
his findings in various journals, such as the Astrophysical Journal.      namely the Stichting Radiostraling van Zon en Melkweg (SRZM)               astronomy, the Netherlands did not simply follow what was going on            Netherlands, in: Journal of Astronomical History and Heritage, 9,1 (2006), pp.
      During the war, Europe’s access to international publications was   (National Foundation for Radio Astronomy or NFRA).                         elsewhere, but took the lead.                                                 3-20.
restricted. Thanks to Oort’s complaints about this to Bart Bok, a Dutch       The board of the SRZM consisted not only of several astronomers,
astronomer who immigrated to the US in 1929 to work at Harvard            but also of members of the PTT (which was interested in the radio
College Observatory in Cambridge, Bok made sure astronomical              emission of the sun, because this affects the ionosphere and influences
literature from the US reached Holland. These contacts between Oort       radio propagation on the Earth), Philips, and the KNMI (Royal
and Bok were crucial in establishing the relations between the            Netherlands Meteorological Institute).
Netherlands and the US during and after the war. At a meeting of the                                                                                                                                                           Acknowledgments
American Astronomical Society in September 1940, the Council                                                                                                                                                                   We thank Frans Van Lunteren, David Baneke and Martin Weiss for their useful
appointed a Committee for the Distribution of Astronomical Literature                                                  Figure 4. In 1954, the                                                                                  remarks. Further, we thank Colin Purrington of Swarthmore College for placing a
                                                                                                                       observations in Kootwijk                                                       Figure 6. The
(CDAL) with Bart Bok as president.                                                                                                                                                                    Westerbork
                                                                                                                                                                                                                               very useful postertemplate at our disposal.
                                                                                                                       led to the publication of
                                                                                                                       the first large-scale map                                                      telescope
                                  Through this channels, Oort got
                                                                                                                       of the distribution of
                                  familiar with the publications of
                                                                                                                       neutral hydrogen in the
                                  Reber and understood that it was                                                     Galaxy. In 1958, the data
                                  important to find radiation at one                                                   were     combined     with    In the same way as Oort had been pursuing his plans for Dwingeloo
                                  specific frequency. As a result, a                                                   similar ones of the           during the Kootwijk period, he again started planning as early as in
                                  spectral line that could be observed                                                 Southern part of the
                                                                                                                                                     1957 the building of a new telescope. Its creation was a long and
                                                                                                                       Galaxy      observed   by
                                  by a radio telescope had to be
                                  found. Oort asked astronomy
                                                                                                                       Australian astronomers.       complex process, which started as a Dutch/Belgian venture. After the      For further information
                                                                                                                       Together, they formed the     withdrawal of the Belgians, the Dutch had to go on on their own. The      Please contact Drs. Astrid Elbers:
                                  student Henk van de Hulst to                                                         Leiden-Sydney map of the      project resulted in the Westerbork Synthesis Radio Telescope in 1970,     Leiden Observatory, P.O. Box 9513, 2300 RA Leiden ,The Netherlands.
                                  investigate whether such a line                                                      Milky Way.                    an interferometer consisting of a linear array of 14 antennas. Today,     Phone: +31 (0)71 527 8412
                                  existed.                                                                                                           this telescope is still in use.                                           elbers@strw.leidenuniv.nl

 Figure 2. Bart Bok                                                                                                                                                                                                            You can find an on line version of the poster at:
                                                                                                                                                                                                                               http://www.strw.leidenuniv.nl/~elbers/

								
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