Bibliotheken Tentoonstellingen Jan Oort

Jan Oort, Astronomer

A short biography of Jan Hendrik Oort

1. Biography
2. Leiden Observatory
3. Leiden University
4. The Netherlands
5. Galactic rotation
6. Comets
7. Crab Nebula
8. International contacts
9. Mens sana...

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.

Oortklein_21.jpg (2139 bytes)21. J.H. Oort’s Doctoral Thesis, The stars of high velocity. Groningen 1926. Oort’s own copy.

Oortklein_22.jpg (4119 bytes)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 Unpublished in this form: too few data points, therefore unconvincing.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.

Oortklein_23.jpg (3203 bytes)23. J.H. Oort’s correspondence with B. Lindblad, who originated the suggestion of differential rotation around a distant centre.

Oortklein_24.jpg (4807 bytes)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).

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