as an Instructor. Under Otto Struve Yerkes became the leading astrophysics center, when he directed it. In addition to Bidelman, by 1946 the Yerkes astronomy staff included Paul Ledoux, Arne Slettebak, Armin Deutsch, Marshall Wrubel, Arthur D. Code, Carlos Cesco, Víctor M. Blanco, W. W. Morgan, Otto Struve, Jesse L. Greenstein, Gerard P. Kuiper, George Van Biesbroeck, Louis G. Henyey Anne B. Underhill, Guido Münch, Nancy G. Roman, and the two future Nobel Prize winners, Subrahmanyan Chandrasekhar and Gerhard Herzberg. Other astronomers at Yerkes when Bidelman was there were Kaj Strand, W. Albert Hiltner, Aden B. Meinel, and visiting professors Bengt Strömgren from Denmark, and Jan Oort, Hendrik C. van de Hulst and Adriaan Blaauw from the Netherlands. George Herbig, also there, remembered it as an "exciting, stimulating place to work" and a "powerhouse in astronomy" while under Struve's direction. Bidelman spent long hours observing in remote west Texas at McDonald Observatory because he, like other Yerkes faculty, was also an astronomer at the University of Texas (UT). At the suggestion of Struve, the two universities had cooperated to create McDonald Observatory when the UT system had no astronomy department but W. J. McDonald gave them money in 1926 for an observatory, while in Wisconsin, the Yerkes astronomers needed a larger telescope but lacked the funds to obtain one. Otto Struve, who directed both Yerkes and McDonald, has been described as dedicated yet demanding. His managerial style included daily inspections of the faculty to see if they were working. Despite reports of tensions there was also "close knit camaraderie" and "boisterous parties" evidenced by Yerkes "spontaneous party songs" including "The Billy Bidelman Song". Sung to the tune of "The Battle Hymn of the Republic", it consisted of repeating three times the line: "Struve, Kuiper, Hiltner, Morgan, Chandrasekhar too," followed by: "And Billy Bidelman". In 1946, W. W. Morgan and William P. Bidelman published a paper on interstellar reddening using the MK system of spectral classifications and photoelectric photometry. Morgan later said this paper with Bidelman on interstellar reddening was "the principal paper along the way" to the UBV system, which he devised with Harold Johnson. In 1947, Bidelman became first to note the concentration of type M supergiant stars around χ Per, suggesting they were young Population I objects. This group, along with the Double Cluster, was later named the Perseus OB1 Association. Based on its radial velocity, Bidelman also