Eruptions on the sun can have significant effects on our vital infrastructure. For this reason, the KNMI monitors not only the regular weather but also space weather. The most famous case of extreme space weather is the Carrington event of September 1, 1859. At that time, a large geomagnetic storm caused sparks to come from telegraph machines. Rediscovered measurement data in the archives of the KNMI can help investigate what the impact would be if something like this were to happen now.

Geomagnetic measurements date back 170 years 

In addition to the weather, geomagnetism was also closely monitored

Last year we celebrated the 170th anniversary of the KNMI. A few years before the KNMI was founded in 1854, regular measurements were already being taken from Sonnenborgh in Utrecht; the first location of the KNMI. Few people know that in addition to the weather, geomagnetism was also closely monitored. Three times a day, three different magnetic instruments were read. In this way, all directions of the geomagnetic field were determined. The same measurements were made in Den Helder by a predecessor of the current Rijkswaterstaat. 

Two iron-free pavilions in De Bilt 

This type of measurement was certainly not easy. In the city center of Utrecht, measurements were disrupted by passing iron baby carriages. To prevent this, the walkway was first diverted and later a thorn hedge was also placed. When the KNMI moved to De Bilt in 1897, two special iron-free pavilions were built for the observations. However, with the arrival of the electric tram and later the train, there was no future for this type of measurement in De Bilt either. In the mid-1930s, geomagnetic observations were moved to Witteveen in Drenthe. Even there, the construction of the Emmen-Drachten road and the Gasunie pipes had to take the KNMIs measurements into account. 

End of magnetic measurements in the Netherlands 

Carefully tracking the geomagnetic field was not only scientifically interesting at the time but also important for society; think of accurate navigation, for example. Over time, however, the societal importance of having a Dutch measuring station diminished. The geomagnetic field could also be determined using satellites or by utilizing foreign measuring stations. Since the 1980s, geomagnetic measurements have not been conducted by the KNMI due to budget cuts. 

Space weather 

Space weather refers to eruptions on the sun that impact our technology 

Nowadays, the importance of precise geomagnetic measurements is beginning to increase again. As we become increasingly dependent on technologies such as satellites, international electricity or telecom networks, and radio communications, the topic of space weather is becoming more important. Space weather refers to eruptions on the sun that impact our technology.