Cornelis de Jager

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Cornelis de Jager
Kees de Jager in 1967
Born (1921-04-29) 29 April 1921 (age 98)
Residence Den Burg
Alma mater Utrecht University
Spouse(s) Doetie Rienks
Scientific career
Fields astrophysics, climate change
Institutions Utrecht University
Doctoral advisor Marcel Minnaert

Cornelis "Kees" de Jager (born 29 April 1921) is a Dutch astronomer who specializes in predicting solar variation to assess the Sun's impact on future climate. He was the General Secretary of the IAU from 1967 to 1973 and former director of the observatory at Utrecht. He is a fellow with the Committee for Skeptical Inquiry.


Born in Den Burg, de Jager spent his school years in the Dutch East Indies. From 1939 to 1945 he studied mathematics, physics and astronomy at Utrecht University. On 13 October 1952 he obtained his PhD with a thesis called "The Hydrogen Spectrum of the Sun". His supervisor was Marcel Minnaert.

Solar and stellar research

De Jager did work on stars and solar physics, in relation to which he was a founding editor of the journal Solar Physics.[1] In 1980 he was principal investigator of the Hard X-ray Imaging Spectrometer (HXIS) on board the Solar Maximum Mission satellite. His work on solar flares was often done in collaboration with Zdeněk Švestka.

From 1978 onward de Jager did noted work on the most luminous stars, known as hypergiants.[2] From 1960 to 1986 de Jager was a professor at Utrecht University. In 1969 he became member of the Royal Netherlands Academy of Arts and Sciences.[3]

Sun-climate relations

De Jager's current research focuses on predicting solar variation to assess the Sun's impact on future climate. Usually solar activity is defined in terms of the Sun's toroidal magnetic field, the field component parallel to the solar equator. Sunspots are one expression of this component. De Jager introduces the poloidal field of the Sun, which connects its two poles, as a factor of possibly similar importance. He uses proxies for both components and takes 19-year running averages to eliminate all effects that last only one or two solar cycles. Next he plots both components in a diagram, thus creating an experimental phase portrait. The track of the two components went from low to high activity around 1925. Around 2009 the same point has been passed in the opposite direction. Thus solar activity in the 21st century is expected to be lower than it was for most of the 20th century. A reduction in solar activity means less energy input to the Earth, thus counteracting global warming. A book, Grand Phases On The Sun: The case for a mechanism responsible for extended solar minima and maxima, was written to outline some of de Jager's research in this regard, along with contributory papers from Bas van Geel and Sylvia Duhau in 2013.[4]


Expanding on a 1990 paper presentation at the International Skeptics Conference, de Jager published an article for Skeptical Inquirer where he parodies numerology. In Adventures in Science and Cyclosophy, de Jager claims that many times pseudoscientific reasoning ignores coincidences dealing with the relationship between objects when there are unlimited data points. He states that measurements surrounding the Great Pyramids have been used to show a relationship with astronomy. To do so, he explains, anyone can use the law of large numbers[5] to relate to anything one would want, to try and prove there is some connection. As an illustration, he uses the example of his bicycle and the cosmos.[6][7] Enthusiasts in this formula have created a website that allows visitors to submit data to replicate de Jager's experiment.[8]

I measured the diameters of my bike's: -pedals, symbolizing the forward-going dynamics; -front wheel, which directs my ways into the unknown future; -lamp, enlightening my paths; -bell, though which I communicate with encounters. Thus I laid the building stones for a new holistic four-dimensional religion apt to the coming of the New Age of Aquarius: cyclosophy. The measurements were expressed in Holy Bike inches, being 17mm. This is so since 1 is the first prime number and 17 the seventh, and because seven is the holy number. Calling P, W, L and B the four measured quantities, it turns out that P ^ 2 √ L x W = 1823 which is the ratio between the masses of the proton and the electron.... Coincidences occur regularly in numerical experiments, as in daily life ... are not rare ... Most people greatly underestimate the enormous amount of possible combinations between numbers. Adventures in Science and Cyclosophy[9]

According to Kendrick Frazier who attended the 1998 Second World Skeptics Congress in Heidelberg, Germany de Jager's "dead-pan" description of how he took measurements throughout his house showing the "absurdities of those who attach great mystical significance to measurements of the Great Pyramid" had the audience "in stitches" Apparently "His home is in an astronomical observatory, a location, he said, 'that may be very close to the cosmos and well receptive to its incredible powers.'”[10]

Other activities

He was the General Secretary of the IAU from 1967 to 1973 and former director of the observatory at Utrecht.[11] In 1981, de Jager became a founding member of the World Cultural Council.[12] He was the first chairman of Stichting Skepsis from 1987 to 1998,[13] the first chairman of the European Council of Skeptical Organisations from 1994 to 2001,[14] and is also a Committee for Skeptical Inquiry fellow.[15][16] de Jager joined his CSI peers by signing the "Deniers are not Skeptics" petition that asks the media to stop referring to climate change deniers as skeptics.[17]

He spoke on astrology at the World Skeptics Congress in 1996.[18]


The asteroid 3798 de Jager is named for him.[22]



  1. ^ A closing editorial of "Solar Physics" at the Harvard website
  2. ^ "Two Decades of Hypergiant Research" (PDF). festschrift. Retrieved 13 May 2016.
  3. ^ "Kees de Jager". Royal Netherlands Academy of Arts and Sciences. Retrieved 28 July 2015.
  4. ^ Yaskell, S.H., Grand Phases On The Sun: The case for a mechanism responsible for extended solar minima and maxima (Trafford: 2013)
  5. ^ Lee, Adam. "Popular Delusions IX: Numerology". Daylight Atheism. Patheos. Retrieved 28 June 2016.
  6. ^ de Jager, Cornelis. "The Holy Bicycle". Geistige Nanrung Dein Forum. Retrieved 28 June 2016.
  7. ^ Paulos, John Allen. "Irreligion: A Mathematician Explains Why the Arguments for God Just Don't Add Up". Google Books. Google. Retrieved 28 June 2016.
  8. ^ Hars, Florian. "Radosophie". Misz. Retrieved 28 June 2016.
  9. ^ de Jager, Cornelis (1992). "Adventures in Science and Cyclosophy". Skeptical Inquirer. 16 (2): 167–172.
  10. ^ Kendrick, Frazier. "Science and Reason, Foibles and Fallacies, and Doomsdays". CSI. Center for Inquiry. Retrieved 6 June 2016.
  11. ^ Dictionary of minor planet names, Volume 1 page 321 by Lutz D. Schmadel, International Astronomical Union
  12. ^ "About Us". World Cultural Council. Retrieved November 8, 2016.
  13. ^ "Randverschijnselen in de wetenschap – Liber amicorum voor Kees de Jager". Stichting Skepsis website. Stichting Skepsis. Retrieved 28 October 2014.
  14. ^ Mahner, Martin (February 2002). "10th European Skeptics Congress: Rise and Development of Paranormal Beliefs in Eastern Europe". Skeptical Inquirer. CSICOP. 26 (1). Retrieved 28 October 2014.
  15. ^ CSI fellows list
  16. ^ Paranormal claims: a critical analysis by Bryan Farha and Michael Shermer, pg 70
  17. ^ "Deniers are not Skeptics". CSI. Center for Inquiry. Retrieved 6 June 2016.
  18. ^ Flynn, Tom. "World Skeptics Congress Draws Over 1200 Participants". CSI. Center for Inquiry. Retrieved 6 June 2016.
  19. ^ "Recipients of the Karl Schwarzschild Medal". The AG. Astronomische Gesellschaft German Astronomical Society. Retrieved 13 May 2016.
  20. ^ "Previous winners of the George Ellery Hale Prize". Solar Physics Division. American Astronomical Society. Archived from the original on 13 August 2013. Retrieved 13 May 2016.
  21. ^ Kurtz, Paul (1990). "Skepticism in Europe: Brussels Conference Tackles Diverse Issues". Skeptical Inquirer. 15 (2): 221.
  22. ^ Lutz, Schmadel. "Dictionary of Minor Planet Names, Volume 1". Google Books. Springer. Retrieved 28 June 2016.

External links

  • Cornelis de Jager homepage
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