Jan Oort, Astronomer
5. Galactic rotation
In 1927, the Swedish astronomer B. Lindblad published a theory
of galactic structure that had the sun at a considerable distance
from the center, and in which the components of the galaxy rotated
around that center in such a way that on the whole the outlying
components moved somewhat more slowly than those further in. The
publication was heavily mathematical. Oort realized that the theory
had implications for the motions of the stars near the sun, and that
in fact material was available to prove that the theory was correct.
Oort derived the laws for the dependence of the rotation speed on
the distance from the center, introducing two constants, A and B,
that are now generally known as the Oort constants. He also showed
very roughly that the motions of the stars in the solar neighbourhood
show the effects of differential rotation. After publishing these
results, he spent considerable time and effort refining, extending,
and generalizing them, trying to build up a picture of the structure
of the galaxy as a whole.
21. J.H. Oort’s Doctoral Thesis, The stars
of high velocity. Groningen 1926. Oort’s own copy.
22. Diagram of observed vs. theoretical
values of velocities as a function of galactic longitude, with
J.H. Oort’s note: ‘Unsuitable for publication after all’.
Unpublished in this form: too few data points, therefore unconvincing.
Version with more data published in Bulletin of the Astronomical
Institutes of the Netherlands 1927 (4) pp. 79-89 and 94.
23. J.H. Oort’s correspondence with B. Lindblad,
who originated the suggestion of differential rotation around a distant
24. J.H. Oort supplementing his own work. Two
pages from his working copy of ‘Stellar Motions’ (Monthly Notices of
the Royal Astronomical Society 99 (1939), pp. 369-384).