Jacobus Kapteyn

Jacobus Kapteyn

Jacobus Cornelius Kapteyn was born on January 19, 1851 in Barneveld, Gelderland, a small province of the Netherlands.  After creating an impressive reputation for his studies of the Milky Way and discovering evidence for galactic rotation, he died on June 18, 1922, at age 71.  

Kapteyn was a Dutch astronomer who attended the University of Utrecht in 1868 where he studies physics and mathematics.  In 1875, he finished his thesis and proceeded to work at the Leiden Observatory.  He then became a professor at the University of Groningen.  Because he did not have an observatory, he volunteered measuring photographic plates, which were taken by David Gill.  Gill was conducting a survey at the Royal Observatory at the Cape of Good Hope.  The final product contained a list of 454,875 stars in the Southern Hemisphere and their positions and magnitudes.  In 1897, during his volunteer work, Kapteyn discovered a star with the highest proper motion at the time.  It was named “Kapteyn’s Star”.  

In 1904, Jacobus Kapteyn discovered the first extreme evidence of the rotation of our galaxy.  While studying the proper motions of stars, he determined that the motion of stars being random was a misconception.  In fact, stars could be divided in two separate streams moving in opposite directions.  This evidence eventually led to the discovery of galactic rotation, by Bertil Lindbald and Jan Oort.

Two years later, the Dutch astronomer launched a plan in which the radial velocity, proper motion, apparent magnitude, and spectral type would be measured in 206 zones, in order to measure the distribution of stars in the Galaxy.  This plan involved the cooperation of 40 observatories, and was the first coordinated statistical analysis in astronomy.

In 1913, Kapteyn was awarded the prestigious James Craig Watson Medal, a medal awarded by the U.S. National Academy of Sciences for contributions to astronomy.  He then retired in 1921 and returned to work at the Leiden Observatory.  Here, at the age of seventy, he helped upgrade the observatory to contemporary astronomical standards. 

Jacobus Kapteyn’s life-work was published in 1922, shortly before his death.  It consisted of a theory now called “Kapteyn’s Universe”.  In this theory, the universe is described as “lens-shaped” and the density decreased away from the center of it.  Today, this model is deemed accurate in high galactic altitudes, but fails in the galactic plane because of our modern knowledge of interstellar absorption. 

Several things have been named after him in honor of his great contributions to astronomy.  There is a crater on the moon, the “Kapteyn Crater”, which was named after him, and a telescope located on La Palma in the Canary Islands, the “Jacobus Kapteyn Telescope”.

Reviewing Kapteyn’s great legacy in astronomy, it is no wonder why he is so highly regarded in the astronomical world.  His contributions helped us get to where we are today and he deserves all the recognition he has/is receiving.  One cannot help but wonder what more incredible discoveries he would make if he were still living today!

Work Cited

Dictionary of Scientific Biography, C. Gillispie, editor.  Charles Scribner’s Son. 1981

"Jacobus C. Kapteyn." NNDB: Tracking the Entire World. Web. 25 Feb. 2011. <http://www.nndb.com/people/657/000170147/>.

"Jacobus Kapteyn." Citizendium. Web. 25 Feb. 2011. <http://en.citizendium.org/wiki/Jacobus_Kapteyn>.