Jan Hendrik Oort
One of the greatest astronomers of the 20th century, Oort revolutionised astronomy
Jan Oort was a true trailblazer, approaching his astronomical research as both an astronomer and theorist with a broad range of interests. Throughout his established career Oort made remarkable contributions to the discipline and was responsible for numerous groundbreaking discoveries. As such the Oort Cloud, Oort constants and the asteroid 1691 Oort are all named after him.
In his 20s Oort had already determined that the Milky Way rotated like a giant pinwheel, with stars closer to the centre of the galaxy travelling much faster than those further out. Two constants derived by Oort – known as
Oort constants A and B – underpinned this realisation and are still used in calculations of galactic rotation to this day. Through studying the motion of stars, Oort also revealed that our Sun was not at the centre of the Milky Way, but was in fact some 26,000 light years out in the galactic suburbs. Moreover, during his observations of star movement throughout our galactic home, Oort used the term ‘dark matter’ to describe the unidentified mass causing stars to move faster than calculations had predicted.
Ever perceptive, Oort was one of the first scientists to realise the true significance of using radio waves to investigate the cosmos. He theorised that clouds of hydrogen gas were loitering out in the spiral arms of the Milky
Way, and it was in these gaseous plumes that stars were born. Oort predicted this before radio telescopes were able to confirm his theories. After World War II he was able to witness his ideas and theories become reality at the new Dutch radio observatories Dwingeloo and Westerbork.
One of his most notable contributions to astronomy is his theory that a vast reservoir of comets surrounds the Solar System. Though yet to be proven, his theory is widely accepted within the scientific community and has come to be known as the Oort Cloud. Oort had meticulously studied the orbits of long-period comets, noticing that many originated from a zone far beyond the orbit of Pluto. Encompassing the Solar System in a giant spherical shell, the
Oort Cloud is thought to contain billions – if not trillions – of pieces of icy space debris and is home to most of the long-period comets we observe in our Solar System. Oort quite literally rewrote the textbooks on galactic motion and our understanding of the universe.
Born in Franeker in the Netherlands, Oort attended the University of Groningen, where he enrolled at the age of 17 to study astronomy. After graduation he continued to work at the University of Groningen as an assistant for a year, then headed to the US to gain experience working at Yale Observatory for two years.
In 1924 Oort returned to the Netherlands, achieving his doctorate with a thesis titled ‘The Stars of High Velocity’ just two years later. Oort’s research continued throughout World War II, and when the war ended he became the director of the Leiden Observatory, holding this position from 1945 to 1970. During this time Oort was also the general secretary of the International Astronomical Union, serving from 1935 to 1948. Throughout his career Oort won many coveted awards, one of the more prestigious being the Vetlesen Prize from Columbia University, which he won in 1966.
Oort passed away in 1992 at the age of 92.
His revolutionary ideas and discoveries which shook the scientific world continue to shape our understanding of the universe to this day.
“Oort also revealed that our Sun was not at the centre of the Milky Way”