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Leiden University Archives, Observatory, directorate E. Hertzsprung

Identifier: ubl156

Scope and Contents

The papers mostly concern Hertzsprung’s work at Leiden Observatory: management issues, contacts with students, and the maintenance of the scientific instruments of the Observatory. Two important files contain correspondence with other senior staff members: Jan Oort and Piet Oosterhoff. Furthermore here are some research notes.


  • c. 1919-1964
  • Bulk c. 1934-1942


Language of Materials

Mostly Dutch, also German, French and English

Conditions Governing Use

Since the archive is digitized, the original papers are not free for public access, unless with permission of the curator after a written request with motivation. Other regulations that apply during the use of these materials can be found on the website of Leiden University Library.

Biographical / Historical

Ejnar Hertzsprung worked as a photochemical engineer in Denmark, Russia and Germany, before turning to astronomy. Between 1909 and 1919 he worked in Göttingen and Potsdam, before coming to Leiden as professor of astronomy and vice director of the Observatory. In the 1920s he spent several years abroad, working at the Union Observatory in Johannesburg and at Harvard Observatory. In 1934 he succeeded Willem de Sitter as director of the observatory. After his retirement in 1945 (it was postponed because of the Second World War), he returned to Denmark.

Hertzsprung’s main scientific work regarded the establishment of the relation between colour (spectral class) and absolute luminosity of stars, later known as the Hertzprung-Russell diagram. This led to the discovery of giant stars. He also worked on the relation between the light curve and absolute luminosity of variable stars, famously using Cepheid variables to estimate distances to extragalactic objects, and on the relation between mass and luminosity of double stars. Most graduate astronomy students in Leiden were supervised by him.

Hertzsprung was awarded an honorary doctorate of Utrecht University in 1923, the Gold Medal of the Royal Astronomical Society in 1929, and the Bruce Medal in 1937.

He was succeeded as director of the Observatory by Jan Oort.


42 items (c. 0.4 metre)


Archief afkomstig van E. Hertzsprung, hoogleraar sterrenkunde aan de Universiteit Leiden (1919-1945) en directeur van de Leidse Sterrewacht (1934-1945). Dit archief bestaat uit correspondentie en stukken betreffende het beheer van de Leidse Sterrewacht.


Archive created by E. Hertzsprung, professor of astronomy at Leiden University (1919-1945) and director of Leiden Observatory (1934-1945). This archive consists of correspondence and papers regarding the management of the Leiden Observatory.


The inventory consists of the following categories:

Correspondence by correspondent (no. 1-6)
Correspondence by institution (no. 7-12)
Correspondence by subject (no. 13-17A)
Notes, observations and teaching (no. 18-23)
Observatory management (no. 24-30)
Instruments (no. 31-38)

To facilitate researchers, each file has been given a short title. In some cases these titles were original designations by the authors. The other titles are given by the author of this inventory. The main subject of each file is indicated in the inventory. This is not an exhaustive description, but a first indication, intended for researchers.

Correspondence has been ordered alphabetically by correspondent, following the Dutch system (disregarding prefixes such as van, van der etc).

Within the files, correspondence has been ordered chronologically. Other papers are preserved in the order in which they were found.

"Correspondence with ..." indicates that the file contains letters from both correspondents; "letters from …" indicates that only one side of the correspondence has been preserved in this archive.

Physical Location

Leiden University Library, Special Collections

Custodial History

This archive was created by E. Hertzsprung in the course of his work. The papers were preserved in Leiden Observatory until they were transferred to Leiden University Library in 2010.

The files no. 3 and 4 (correspondence with Oort and Oosterhoff) were donated to Leiden University Library by J.H. Oort and P.Th. Oosterhoff in 1967. They were registered as ms. BPL 2748 and BPL 2749. They have now been transferred to the Observatory Archives.

Immediate Source of Acquisition

The archive was transferred to Leiden University Library in 2010, by agreement between Leiden Observatory, the Leiden University Library and the Department of Documentary Information and Archive Administration of Leiden University.


In once case, only a selection of a file has been preserved. This concerns a box of notebooks containing luminosity estimates of variable stars on Harvard plates. Some of these notebooks have been preserved, by way of example.


No future additions are to be expected.

Existence and Location of Copies

The archive is digitized. The images are available in the inventory.

Related Materials

This archive is part of Leiden Observatory Archives, which contain the papers of the Observatory and its directors from c. 1830-1945.

The collection of Leiden University Library also includes the scientific papers of Jan Oort (director of the Observatory from 1945-1970).

Separated Materials

The main part of Hertzsprung’s personal and professional archive is preserved at the Institut for Videnskabsistorie of Aarhus University, Denmark.


  • Baneke, D., Teach and travel. Leiden Observatory and the renaissance of Dutch astronomy in the Interwar years, Journal for the History of Astronomy, 2010.
  • DeVorkin, D., Stellar Evolution and the Origin of the Hertzsprung-Russell Diagram, in: O. Gingerich (ed.), Astrophysics and Twentieth-Century Astronomy to 1950, Part A (Cambridge 1984) 90-108.
  • Herk, G. van, H. Kleibrink en W. Bijleveld, De Leidse sterrewacht. Vier eeuwen wacht bij dag en nacht (Zwolle 1983).
  • Herrmann, D.B., Ejnar Hertzsprung, Pionier der Sternforschung (Berlijn etc. 1994).
  • Katgert-Merkelijn, J.K., De opvolging van W. de Sitter in: Leids Jaarboekje (1997) 128-143.

Processing Information

The papers have been reordered and repacked. The original files were maintained as much as possible. Obviously misfiled papers have been refiled, and obviously related papers have been put together, while obviously unrelated papers have been separated.

Beschrijving van de Leiden Observatory Archives, directorate E. Hertzsprung
David Baneke, 2010
Language of description
Script of description
Code for undetermined script
Language of description note
Beschrijving is in het Engels.

Revision Statements

  • 10 September 2015: latest update

Repository Details

Part of the Leiden University Libraries Archives & Collections Repository

Leiden Witte Singel 27 2311 BG Netherlands
+31 71 527 2857