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Leiden astronomer Henk van de Hulst: humble man with great authority

World-famous among astronomers, humble, and averse to conventions. On 23 April, the Dutch biography about Henk van de Hulst was published. Biographer Dirk van Delft: ‘This remarkable man deserved a biography.’

Interview: Bryce Benda

Why a biography about Henk van de Hulst?

‘Henk van de Hulst is unknown to many people, but within astronomy he is a celebrity. He is also interesting because of his versatility: he was active in astronomy and space research, but he was also very influential in management positions. For instance, he was at the forefront of the European Space Agency (ESA) and without Van de Hulst's intervention, ESTEC would not be located in Noordwijk today.’

DIRK VAN DELFT (1951) was Extraordinary Professor of Material Heritage of the Natural Sciences in Leiden, Director of Rijksmuseum Boerhaave and Chief Science at NRC Handelsblad. In 2015, he won the NWO Eureka Prize for science communication with his biography/dissertation on Heike Kamerlingh Onnes. Four years later followed a hefty biography of the great Dutch physicist Hendrik Antoon Lorentz.  

I must confess that I had never heard of Henk van de Hulst. Why is he unknown to the general public? 

‘Van de Hulst was a rather reserved person. He knew what he was worth, but he did not blow his own horn. 
He also was active in various fields. The more famous astronomer Jan Hendrik Oort was more focused on one subject, namely radio astronomy. Van de Hulst operated more in the background, and occupied himself with several subjects.’ 

Which themes are the most important in his career?

‘You could divide his work into three main themes: light scattering, space research and radio astronomy. The book that Van de Hulst wrote about light scattering has been cited very often, much more often than Oort's work. This is because his research into light scattering is not only useful within astronomy, but also outside it. For example, it can be used to look under your skin with laser light, in cancer research. But also in research into paint or milk.

As far as space research is concerned, Van de Hulst's international stature meant he had excellent contacts at NASA. Thanks in part to his efforts and network, the first Dutch satellites, the ANS and the IRAS, were able to travel on American launchers.

And then there was radio astronomy. As a student in Utrecht in 1944, Van de Hulst predicted the existence of the 21 cm hydrogen line in radio astronomy, an emission line with which you can observe hydrogen atoms in space. His prediction eventually prompted the construction of the radio telescope at Dwingeloo, and using the 21 cm line Van de Hulst and Oort discovered that the Milky Way has a spiral structure.’

In April 1944, Henk van de Hulst predicted the existence of the 21 cm hydrogen line in radio astronomy at a colloquium in Leiden. Here is a re-enactment of his 1956 lecture for a documentary. © Leiden Observatory
At the 1962 COSPAR conference in Washington, Van de Hulst carried Dutch clogs for cosmonaut Titov and astronaut Glenn. ‘Carved from wood from the same tree, meant to be worn together.’

What makes Van de Hulst so special as a person?

‘He was brought up a strict Christian and you could really see the characteristics associated with Christianity in him. For example, he dedicated himself to the community without wanting anything in return. He spent a lot of time building up ESA and was chairman of the Dutch committee for space research. He is therefore also seen as the father of space research in the Netherlands. 

He also had a great sense of humour. At the Dies of Leiden University, professors may pin their medals to their robes, which many do. At one of the editions Van de Hulst suddenly turned up with all sorts of medals. When one of his colleagues inspected them more closely, they all turned out to be skating medals! 

So he was averse to conventions. While his colleagues walked around in suits, he walked around barefoot or on sneakers. At the same time, he was incredibly smart, friendly, and gave people space. He had great authority, was authentic, didn't mess with anyone and was incredibly respected for all that.’

After writing this biography, do you feel you know him? 

‘Before Van de Hulst died in 2000, I saw him walking around at the Leiden Observatory. But I never really spoke to him. Fortunately there are still many people alive who knew him well, in contrast to when I was writing the Lorentz biography. I have spoken to more than thirty people, including former PhD candidates of Henk, colleagues and family members. They came up with all sorts of nice anecdotes, so then suddenly a person comes much closer.’ 

Three days after the launch of the Hubble Space Telescope on tea visit at Erwin Cohen's house in Orlando (Florida), April 1990 (Wim van de Hulst collection).
Lorentz biography by Frits Berends en Dirk van Delft (2019)

Your biography about Lorentz came out at the end of 2019, how did you manage to write a new biography so quickly?

‘I started when the biography about Lorentz was finished. I'm also a bit of a workaholic, I spend 70 hours a week on a book like this. Besides, I don't need much sleep, I like to work really hard and it helps that I have the necessary writing experience. But don't worry, it took more than three thousand hours to write this book, haha.’ 

This was your third biography. What makes writing a biography so appealing?

‘Writing is my passion and my life, I prefer to write day and night. I love non-fiction: unravelling a subject, going into the archives, and then writing it down as beautifully as possible. The joy of writing a biography is that you are not only dealing with an interesting subject, but with flesh and blood as well. That is what I find most interesting. How do people treat each other? Is there hatred and envy? What moves these people? You find that everywhere, also in science. That extra layer makes me want to dive in with great pleasure.’

What will be your next biography?

‘I am currently working on an exciting short story: Abdul Khan's atomic espionage in the 1970s. He stole nuclear secrets from the ultracentrifuge in Almelo in the Netherlands, which he used to help his homeland Pakistan get an atom bomb. I am writing a portrait of technical photographer Frits Veerman, who died this year. He discovered the espionage and became a whistleblower. But instead of being a national hero, he became a pariah, chased by the security service. 

Next, I will deal with Antoni van Leeuwenhoek, a Dutch amateur scientist from the 17th century. He is known for his home-built microscopes and is the father of microbiology. In 2023 he will have been dead for 300 years, so a good opportunity for a biography.’   

Finally, do you have any advice for aspiring biographers?

‘The trick is to have both a nice person, in terms of life and views, and a fascinating subject. A biography works best when these two things come together.’ 

On June 17, 1946, Henk received his doctorate for the thesis Optics of spherical particles. During the promotion dinner he was flanked by his mother and Miep Coelingh, Minnaert's wife. At the head of the table was Dedde de Jong. On the left promoter Marcel Minnaert, Wil and Jan Hendrik Oort. © Jochmann Disco
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