1. Schlesinger's Telescope: A History of the Yale 26-inch Refractor in The Commonwealth William van Altena and Dorrit Hoffleit Yale University (IAU Commission 8 - July 16, 2003)

2. Frank Schlesinger (1871-1943) Yerkes (1903-1905) –40-inch refractor and the first modern parallax program. Allegheny (1905-1920) –30-inch refractor - design, construction and parallax program. Yale (1920-1943) –26-inch refractor - design, construction and parallax program.

3. Schlesinger at Allegheny Develops astrometric methods for most of the 20th century. Designs and builds the first large refractor for astrometry. Establishes first large-scale parallax program. Schlesinger with optician James McDowell and the Allegheny 30-inch objective (1914).

4. Schlesinger moves to Yale Begins planning for a Southern Station even before moving in 1920. –Plans a southern extension of the Allegheny program. Site survey in New Zealand is promising, but did not match image quality of US west. Invited to explore sites in South Africa –Adopted Univ. Witwatersrand in Johannesburg.

5. Johannesburg is selected!

6. Site preparation for 26-inch Foundation work begins in Feb. 1925. The South Pier of the English-type mounting is constructed.

7. Telescope in Mason Lab. Constructed at Yale in New Haven Design by Schlesinger with Roland Sellew Cross-axis English-type Mounting Forced-air cooling of objective lenses

8. Schlesinger leaves for the South December 1924

9. Telescope is installed Schlesinger ensures that only on-meridian observations will be made! Yale Cottage and the “Dome”

10. The HRH Prince of Wales Dedicates Telescopes! 26-inch with F. Schlesinger (June 22, 1925) Jodrell Bank with B. Lovell & A. Lyne (April 28, 2003)

11. Harold Alden is the first director Director of the Southern Station from 1925-1945. Implemented the extension of Schlesinger’s Allegheny parallax program to the south. Returned to US to direct McCormick Observatory in 1945.

12. Open house in April 1936

13. Parallax errors

14. Yale-Columbia Southern Station Financial and logistical strains of operating the 26-inch begin to arise in 1943. –Talks start with Columbia University. Columbia joined Yale in 1946 in the first of three ten-year agreements. Columbia was interested primarily in photometry of stars and clusters. Dirk Brouwer assumes Yale directorship following Schlesinger’s death in 1943.

15. The move to Australia in 1952 In 1948 increasing light and smog pollution leads Brouwer to look at other sites for the YCSO. R. v. d. R. Wooley invites YCSO to Australia, Brouwer visits the Commonwealth Obs. in 1950. Affiliation with the ANU an important factor in the move.

16. Mt. Stromlo Observatory

17. Changing research interests Fully operational in 1958 after many delays. Disillusioned by small percentage of clear nights on Mt. Stromlo. Brouwer was more interested in proper motions and fundamental systems than parallaxes. After extensive site surveys Brouwer selected a site in Argentina for the new YCSO. Last plate taken with the 26-inch under the auspices of the YCSO was on May 28, 1963 - #69,950. 26-inch refractor donated to the Australian National University.

18. Schlesinger’s Legacy Cape and Yale provided all of the parallaxes in the Southern Hemisphere until the Hipparcos Catalog was published in 1997. Schlesinger started two of the four major parallax programs (Allegheny & Yale) and he trained the director of the third program (McCormick). About 2000 parallaxes and many stellar masses were determined with the 26-inch refractor. Schlesinger’s analysis methods were used until the 1960s, when computers became generally available.

19. Telescope use after 1963 P. A. Ianna and collaborators (Univ. of Virginia) extend the McCormick parallax program to the southern hemisphere (1977-1992). Second-epoch photographs taken of star clusters for membership determinations using proper motions. Amateur astronomer projects. In the final years the building was used as a night club and meeting hall after the dome became too fragile to turn. Plans were being made to replace the dome so that the telescope could be used by the amateur astronomers.

20. Mt. Stromlo Observatory is Destroyed by a Firestorm On January 18, 2003 a firestorm destroyed all telescopes on Mount Stromlo, the workshop, library and many of the residences. Nearly 500 homes in the Canberra were also destroyed. Previously, on February 5, 1952 a fire destroyed the workshop and the machine tools, but almost everything else in the complex was saved.

21. Dome exterior 2003

22. Dome interior 2003

23. Acknowledgements We are grateful to The Commonwealth for hosting the Schlesinger 26-inch refractor during its many productive years in South Africa and Australia under the evolving auspices of: – The University of Witwatersrand The Yale Southern Station The Yale-Columbia Southern Station – The Commonwealth Observatory, Mt. Stromlo Observatory and the Research School of Natural Sciences of the Australian National University. The Yale-Columbia Southern Station