Renowned Dutch astronomer Kees de Jager dies aged 100

Kees de Jager in 1953. Photo: Sonnenborgh archive

To celebrate De Jager's one-hundredth birthday, a bronze plaque bearing his image was mounted on the façade of the Sonnenborgh Observatory in Utrecht on the 29th of April.

Between 1964 and 1977, De Jager was director of the Utrecht Astronomical Institute, located in Sonnenborgh. His connection with the building, however, went much further. During the Second World War, he and a fellow student went into hiding in the vaults under Sonnenborgh. He also lived in the striking building on Utrecht's singel canal for 40 years.

Due to his frail health, De Jager was not able to attend the inauguration of the plaque, but he participated online. You can watch the hommage here.

De Jager passed away last Thursday in Den Burg, on the Texel island.

Kees de Jager obtained his doctorate cum laude in 1952 in Utrecht, supervised by the renowned Flemish astronomer Marcel Minnaert. In his research, de Jager looked at the hydrogen lines in the solar spectrum. Later, his interest shifted to researching solar flares, supergiants and hypergiants. In 1960, De Jager became professor of stellar astrophysics.

He was also a pioneer in Dutch space research. In 1961, de Jager founded the Laboratory for Space Research, the forerunner of today's SRON). He was its first director until 1983. It was partly thanks to de Jager that, in the mid-1970s, the first Dutch satellite (Astronomical Netherlands Satellite; ANS) was launched. De Jager retired in 1984.

De Jager was best known for popularising astronomy and giving countless lectures. The Dutch term ‘oerknal’, which refers to the big bang, was coined by him.

He was also known for his strong opposition to pseudoscience. In 1987, he became the first chairman of the Skepsis Foundation, which promotes critical and scientifically responsible thinking.

Hard pill to swallow
In 2003, he moved from the Utrecht Observatory to his native island, Texel. There, as a volunteer at the Royal Netherlands Institute for Sea Research, he investigated the influence of the sun on climate change. In addition, he continued to participate in running competitions until he was of old age. At the age of 75, he ran the New York marathon.

In 2011, the Faculty of Science decided to stop researching astronomy, which was a hard pill to swallow for De Jager. In a TV show about his life in 2016, he said: “I was numb for a while. I couldn't understand it and I still can't understand it (...) . That they have brought this to ruin.”