![Jacobus Kapteyn00](https://upload.wikimedia.org/wikipedia/commons/9/92/Jacobus_Kapteyn00.jpg)
Prof Jacobus Cornelius Kapteyn
FRS FRSE
Fellowship of the Royal Society of Edinburgh (FRSE) is an award granted to individuals that the Royal Society of Edinburgh, Scotland's national academy of science and letters, judged to be "eminently distinguished in their subject". This soci ...
LLD (19 January 1851 – 18 June 1922) was a Dutch
astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...
. He carried out extensive studies of the
Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
and was the discoverer of evidence for
galactic rotation. Kapteyn was also among the first to suggest the existence of dark matter using stellar velocities as early as 1922.
Kapteyn's family and early life
Kapteyn was born in
Barneveld in the Netherlands to Gerrit J. and Elisabeth C. (née Koomans) Kapteyn, and was one of 15 children.
Many of the Kapteyns were gifted in mathematics and physics.
He passed his entrance exams for university at the age of 16 but Kapteyn's parents wouldn't allow him to go until the following year.
He went to the
University of Utrecht
Utrecht University (UU; nl, Universiteit Utrecht, formerly ''Rijksuniversiteit Utrecht'') is a public research university in Utrecht, Netherlands. Established , it is one of the oldest universities in the Netherlands. In 2018, it had an enrollme ...
to study
mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
and
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
in 1868. He did very well in his studies and when he graduated he was
magna cum laude
Latin honors are a system of Latin phrases used in some colleges and universities to indicate the level of distinction with which an academic degree has been earned. The system is primarily used in the United States. It is also used in some So ...
.
This laid the foundation for his later career.
Jacobus Kapteyn was a very doting father during the earlier years in his career and took an interactive role which during the 1880s was not done much by fathers.
When Kapteyn's children reached schooling age both his daughters, Jacoba Cornelia and Henrietta, and his son, Gerrit, went to a boys' school.
His daughters later made significant strides for women by going to university to read law and medicine.
His daughter Henrietta (1881–1956) married astronomer
Ejnar Hertzsprung
Ejnar Hertzsprung (; Copenhagen, 8 October 1873 – 21 October 1967, Roskilde) was a Danish chemist and astronomer.
Career
Hertzsprung was born in Frederiksberg, Denmark, the son of Severin and Henriette. He studied chemical engineering at Cop ...
and gave him a granddaughter named Rigel.
Career
In 1875, after having finished his
thesis
A thesis ( : theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: ...
, he worked for three years at the
Leiden Observatory
Leiden Observatory ( nl, Sterrewacht Leiden) is an astronomical institute of Leiden University, in the Netherlands. Established in 1633 to house the quadrant of Rudolph Snellius, it is the oldest operating university observatory in the world, with ...
.
In 1878 Kapteyn was inducted as the first
professor
Professor (commonly abbreviated as Prof.) is an Academy, academic rank at university, universities and other post-secondary education and research institutions in most countries. Literally, ''professor'' derives from Latin as a "person who pr ...
of astronomy and theoretical
mechanics
Mechanics (from Ancient Greek: μηχανική, ''mēkhanikḗ'', "of machines") is the area of mathematics and physics concerned with the relationships between force, matter, and motion among physical objects. Forces applied to objects r ...
at the
University of Groningen
The University of Groningen (abbreviated as UG; nl, Rijksuniversiteit Groningen, abbreviated as RUG) is a Public university#Continental Europe, public research university of more than 30,000 students in the city of Groningen (city), Groningen in ...
.
Also at Groningen, he founded the Astronomical Laboratory in 1896 and consequently became the director of the facility.
Kapteyn fulfilled both occupational roles as professor and director at Groningen until his retirement in 1921.
In 1888 he became a member of the
Royal Netherlands Academy of Arts and Sciences
The Royal Netherlands Academy of Arts and Sciences ( nl, Koninklijke Nederlandse Akademie van Wetenschappen, abbreviated: KNAW) is an organization dedicated to the advancement of science and literature in the Netherlands. The academy is housed ...
.
Between 1896 and 1900, lacking an observatory, he volunteered to measure
photographic plate
Photographic plates preceded photographic film as a capture medium in photography, and were still used in some communities up until the late 20th century. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinn ...
s taken by
David Gill, who was conducting a photographic survey of
southern hemisphere stars at the
Royal Observatory at the Cape of Good Hope. To measure these plates he used a special
parallactic instrument that Kapteyn himself had constructed. The results of this collaboration was the publication of ''
Cape Photographic Durchmusterung
In astronomy, Durchmusterung or Bonner Durchmusterung (BD) is an astrometric star catalogue of the whole sky, compiled by the Bonn Observatory in Germany from 1859 to 1903. The name comes from ('run-through examination'), a German word used for ...
'', a catalog listing positions and magnitudes for 454,875
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s in the
Southern Hemisphere.
In 1897, as part of the above work, he discovered
Kapteyn's Star
Kapteyn's Star is a class M1 red subdwarf about 12.83 light-years from Earth in the southern constellation Pictor; it is the closest halo star to the Solar System. With a magnitude of nearly 9 it is visible through binoculars or a teles ...
. It had the highest
proper motion
Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
of any star known until the discovery of
Barnard's Star
Barnard's Star is a red dwarf about six light-years from Earth in the constellation of Ophiuchus. It is the fourth-nearest-known individual star to the Sun after the three components of the Alpha Centauri system, and the closest star in the ...
in 1916.
In 1904, studying the
proper motion
Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
s of stars, Kapteyn reported that these were not random, as it was believed in that time; stars could be divided into two streams, moving in nearly opposite directions. It was later realized that Kapteyn's data had been the first evidence of the rotation of our Galaxy, which ultimately led to the finding of
galactic rotation by
Bertil Lindblad
Bertil Lindblad (Örebro, 26 November 1895 – Saltsjöbaden, outside Stockholm, 25 June 1965) was a Swedish astronomer.
After finishing his secondary education at Örebro högre allmänna läroverk, Lindblad matriculated at Uppsala Univer ...
and
Jan Oort
Jan Hendrik Oort ( or ; 28 April 1900 – 5 November 1992) was a Dutch astronomer who made significant contributions to the understanding of the Milky Way and who was a pioneer in the field of radio astronomy. His ''New York Times'' obituary ...
.
In 1906, Kapteyn launched a plan for a major study of the distribution of stars in the Galaxy, using counts of stars in different directions. The plan involved measuring the
apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
,
spectral type
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...
,
radial velocity
The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
, and
proper motion
Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
of stars in 206 zones. This enormous project was the first coordinated statistical analysis in astronomy and involved the cooperation of over forty different observatories.
Around 1913 Kapteyn developed a theory of how stars were made based on his observations of irregular nebulae and their velocities.
He theorized that stars in irregular nebulae eventually evolved into planetary nebulae.
Although this theory is not entirely correct it did have some redeeming qualities.
He was awarded the
James Craig Watson Medal 400px, James Craig Watson Medal
The James Craig Watson Medal was established by the bequest of James Craig Watson, an astronomer the University of Michigan between 1863 and 1879, and is awarded every 1-4 years by the U.S. National Academy of Scienc ...
in 1913. The year of 1920 Kapteyn took a part-time job at University of Leiden after leaving the university of Groningen.
This move made Kapteyn able to see his granddaughter Rigel and his daughter Henrietta.
In Kapteyn's later years of work he spent his time working on the combination of his life's work revising and editing the Kapteyn Universe.
Kapteyn later retired in 1921 at the age of seventy, but on the request of his former student and director of
Leiden Observatory
Leiden Observatory ( nl, Sterrewacht Leiden) is an astronomical institute of Leiden University, in the Netherlands. Established in 1633 to house the quadrant of Rudolph Snellius, it is the oldest operating university observatory in the world, with ...
Willem de Sitter, Kapteyn went back to Leiden to assist in upgrading the observatory to contemporary astronomical standards.
The astronomy institute of the
University of Groningen
The University of Groningen (abbreviated as UG; nl, Rijksuniversiteit Groningen, abbreviated as RUG) is a Public university#Continental Europe, public research university of more than 30,000 students in the city of Groningen (city), Groningen in ...
is named after Kapteyn. A street in the city of Groningen is also named after Kapteyn: the J.C. Kapteynlaan. And the
Isaac Newton Group of Telescopes
The Isaac Newton Group of Telescopes or ING consists of three optical telescopes: the William Herschel Telescope, the Isaac Newton Telescope, and the Jacobus Kapteyn Telescope, operated by a collaboration between the UK Science and Technology Fac ...
on
La Palma
La Palma (, ), also known as ''La isla bonita'' () and officially San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of making it the fifth largest of the eight main Canary Islands. The ...
in the
Canary Islands
The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...
named the
Jacobus Kapteyn Telescope
The Jacobus Kapteyn Telescope or JKT is a 1-metre optical telescope named for the Dutch astronomer Jacobus Kapteyn (1851-1922) of the Isaac Newton Group of Telescopes at the Roque de los Muchachos Observatory on La Palma in the Canary Islands, Sp ...
(JKT) after him.
The Kapteyn Universe
The structure and size of the galaxy was of great interest to many astronomers during Kapteyn's time. Around 1900, Hugo von Seeliger made an attempt at discerning the structure of the galaxy by making counts of stars between successive magnitudes.
Ultimately, von Seeliger was able to determine the rates at which the galaxy was diminishing in multiple different areas of the sky. In 1901, Kapteyn employed the proper motions technique and derived a statistical approach that allowed him to estimate the average distance to stars between successive magnitudes, effectively providing a scale for von Seeliger's discoveries.
Conclusive results from von Seeliger and Kapteyn estimated the galaxy to be an oblate star system approximately 10 kpc in width and 2 kpc in thickness, the Sun being relatively close (0.6 kpc) to the center.
Using the method of star counts, Kapteyn was able to confirm his results and dubbed his findings as his first model of the galaxy.
Despite having made great strides and providing a model for the galaxy, there was one major issue. Kapteyn's work was based on an unproven presumption, that is, there is no light absorption in space.
If there were light absorption in space, then stars would look more faint, thus, seeming further away than they actually are. Light absorption would also cause the galaxy to disperse more quickly than it actually does. If light absorption proved to be a considerable factor, then Kapteyn's work, or at least his conclusions, would more or less be obsolete. To circumvent this dilemma, Kapteyn spent years studying and measuring the amount of absorption. In 1917, Kapteyn's assumptions on interstellar absorption were debated.
The arguments were centered around an issue with the "zone of avoidance".
By 1918, he was convinced light absorption was of negligible amounts and confidently stood behind his first model for the structure of the galaxy.
Kapteyn had presented his findings in his life's work, ''First Attempt at a Theory of the Arrangement and Motion of the Sidereal System,'' which was published in 1922. Kapteyn's model and distance scale were challenged by
Anton Pannekoek
Antonie “Anton” Pannekoek (; 2 January 1873 – 28 April 1960) was a Dutch astronomer, philosopher, Marxist theorist, and socialist revolutionary. He was one of the main theorists of council communism (Dutch: ''radencommunisme'').
Biograph ...
and
Harlow Shapley
Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal.
Shapley used Cepheid variable stars to estim ...
, among others, but Kapteyn was not well enough to meet with his peers and discuss his work.
He died in June 1922, soon after its publishing.
It was only after Kapteyn's death that
Robert Trumpler
Robert Julius Trumpler (until 1915 Robert Trümpler, born October 2, 1886 in Zürich, Switzerland; died September 10, 1956 in Berkeley, California, Berkeley, United States) was a Switzerland, Swiss-United States, American astronomer.
Career
After ...
determined that the amount of
interstellar reddening
In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Interstellar extinction was first documented as such in 1930 by Robert Julius Trumple ...
was actually much greater than had been assumed. This discovery estimated the size of the galaxy to be about 2.5 times larger than initially was thought, with the Sun replaced to a distance of 9.2 kpc from the
Galactic Center
The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact rad ...
.
Honours
Awards
*
Gold Medal of the Royal Astronomical Society
The Gold Medal of the Royal Astronomical Society is the highest award given by the Royal Astronomical Society (RAS). The RAS Council have "complete freedom as to the grounds on which it is awarded" and it can be awarded for any reason. Past awar ...
(1902)
*
James Craig Watson Medal 400px, James Craig Watson Medal
The James Craig Watson Medal was established by the bequest of James Craig Watson, an astronomer the University of Michigan between 1863 and 1879, and is awarded every 1-4 years by the U.S. National Academy of Scienc ...
(1913)
*
Bruce Medal
The Catherine Wolfe Bruce Gold Medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. It is named after Catherine Wolfe Bruce, an American patroness of astronomy, and was firs ...
(1913)
Named after him
*
Kapteyn (crater)
Kapteyn is a lunar impact crater that is near the eastern limb of the Moon, to the west of the crater La Pérouse. West of Kapteyn is the slightly smaller Barkla, and farther to the west-northwest is the prominent Langrenus. Von Behring is t ...
on the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
*
Asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere.
...
818 Kapteynia
*
Kapteyn's Star
Kapteyn's Star is a class M1 red subdwarf about 12.83 light-years from Earth in the southern constellation Pictor; it is the closest halo star to the Solar System. With a magnitude of nearly 9 it is visible through binoculars or a teles ...
*
Kapteyn Astronomical Institute
The Kapteyn Astronomical Institute is the department of astronomy of the University of Groningen
The University of Groningen (abbreviated as UG; nl, Rijksuniversiteit Groningen, abbreviated as RUG) is a Public university#Continental Europe, pu ...
at the University of Groningen
*
Jacobus Kapteyn Telescope
The Jacobus Kapteyn Telescope or JKT is a 1-metre optical telescope named for the Dutch astronomer Jacobus Kapteyn (1851-1922) of the Isaac Newton Group of Telescopes at the Roque de los Muchachos Observatory on La Palma in the Canary Islands, Sp ...
(JKT) at La Palma, one of the
Canary islands
The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...
*
Kapteyn Package, Astronomical package for Python
References
External links
History of the Kapteyn Institute
{{DEFAULTSORT:Kapteyn, Jacobus
1851 births
1922 deaths
People from Barneveld
19th-century Dutch astronomers
Utrecht University alumni
University of Groningen faculty
Recipients of the Bruce Medal
Recipients of the Gold Medal of the Royal Astronomical Society
Foreign Members of the Royal Society
Foreign associates of the National Academy of Sciences
Corresponding members of the Saint Petersburg Academy of Sciences
Members of the Royal Netherlands Academy of Arts and Sciences
Honorary Fellows of the Royal Society of Edinburgh
Recipients of the Pour le Mérite (civil class)