Cornelis de Jager
Encyclopedia
Education
He spent his school years in the Dutch East IndiesDutch East Indies
The Dutch East Indies was a Dutch colony that became modern Indonesia following World War II. It was formed from the nationalised colonies of the Dutch East India Company, which came under the administration of the Netherlands government in 1800....
. From 1939 to 1945 he studied mathematics
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
, physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
and astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
at Utrecht University
Utrecht University
Utrecht University is a university in Utrecht, Netherlands. It is one of the oldest universities in the Netherlands and one of the largest in Europe. Established March 26, 1636, it had an enrollment of 29,082 students in 2008, and employed 8,614 faculty and staff, 570 of which are full professors....
. On 13 October 1952 he obtained his Ph. D. with a thesis called 'The Hydrogen Spectrum of the Sun'. His supervisor was Marcel Minnaert
Marcel Minnaert
Marcel Gilles Jozef Minnaert was a Belgian astronomer.He obtained a PhD in biology at Ghent University in 1914....
.
Solar and Stellar Research
Kees de Jager did work on stars and Solar physicsSolar physics
For the physics journal, see Solar Physics Solar physics is the study of our Sun. It is a branch of astrophysics that specializes in exploiting and explaining the detailed measurements that are possible only for our closest star...
, in relation to which he was a founding editor of the journal Solar Physics
Solar Physics (journal)
Solar Physics a journal for solar and solar-stellar research and the study of solar terrestrial physics. It was founded in 1967 by solar physicist Cornelis de Jager and publisher D. Reidel. The journal treats all aspects of solar physics, ranging from the internal structure of the Sun and its...
. In 1980 he was principal investigator
Principal investigator
A principal investigator is the lead scientist or engineer for a particular well-defined science project, such as a laboratory study or clinical trial....
of the Hard X-ray Imaging Spectrometer (HXIS) on board the Solar Maximum Mission
Solar Maximum Mission
The Solar Maximum Mission satellite was designed to investigate solar phenomenon, particularly solar flares. It was launched on February 14, 1980....
satellite.
From 1978 onward Kees de Jager did noted work on the most luminous stars, also known as hypergiant
Hypergiant
A hypergiant is a star with a tremendous mass and luminosity, showing signs of a very high rate of mass loss.-Characteristics:...
s.
From 1960 to 1986 de Jager was a professor at Utrecht University.
Sun-Climate relations
De Jager's current research focuses on predicting solar variationSolar variation
Solar variation is the change in the amount of radiation emitted by the Sun and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle . The changes also have aperiodic fluctuations...
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
Proxy (statistics)
In statistics, a proxy variable is something that is probably not in itself of any great interest, but from which a variable of interest can be obtained...
for both components and takes 19-year running averages to eliminate all effects that last only one or two solar cycle
Solar cycle
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...
s. Next he plots both components in a diagram, thus creating an experimental phase portrait
Phase portrait
A phase portrait is a geometric representation of the trajectories of a dynamical system in the phase plane. Each set of initial conditions is representated by a different curve, or point....
. 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 21th 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
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
.
Other Activities
He was the General Secretary of the IAUInternational Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
from 1967 to 1973 and former director of the observatory at Utrecht
Utrecht
Utrecht is a city in the Netherlands.The name may also refer to:* Utrecht , of which Utrecht is the capital* Utrecht , including the city of Utrecht* Bishopric of Utrecht* Roman Catholic Archdiocese of Utrecht...
. He is also a Committee for Skeptical Inquiry fellow.
Awards
- 1974 Karl Schwarzschild MedalKarl Schwarzschild MedalThe Karl Schwarzschild Medal, named after the astrophysicist Karl Schwarzschild, is an award presented by the Astronomische Gesellschaft to eminent astronomers and astrophysicists.-Recipients:...
- 1984 Prix Jules JanssenPrix Jules JanssenThe Prix Jules Janssen is the highest award of the French Astronomical Society. Created in 1897 and awarded annually, it is usually given in alternate years to a French astronomer, and to an astronomer of another nationality. It is distinct from the Janssen Medal , which is awarded by the French...
- 1988 George Ellery Hale PrizeGeorge Ellery Hale PrizeThe George Ellery Hale Prize, or Hale Prize, is awarded annually by the Solar Physics Division of the American Astronomical Society for outstanding contributions over an extended period of time to the field of solar astronomy. The prize is named in memory of George Ellery Hale.Past winners of the...
The asteroid 3798 de Jager
3798 de Jager
3798 de Jager is a main-belt asteroid discovered on October 16, 1977 by Cornelis Johannes van Houten, Ingrid van Houten-Groeneveld and Tom Gehrels at Palomar Observatory. It is named after the Dutch astronomer Cornelis de Jager.- External links :*...
is named for him.