Bidelman directed the Warner and Swasey Observatory from 1970 to 1975, and was a professor of astronomy from 1970 to 1986. In June 1970, Bidelman began as chairman and Director. Bidelman's office was at the old Taylor Road Observatory, given to the university by the Warner & Swasey Company in 1920. Due to light pollution from the city of Cleveland, by the 1950s viewing was difficult and the Burrell Schmidt telescope was relocated ~30 miles away to Geauga County.
In 1973, Bidelman and MacConnell provided data on a variety of B-emission (Be) and shell stars, peculiar stars, weak-metal stars and other bright stars of the southern hemisphere, covering ~81% of the southern sky. They said when completed, Houk's more comprehensive study would "provide spectral date of inestimable value to stellar astronomers" and should supersede their report, but they did it as an "early result" study. Using CTIO objective –prism plates they found nearly 800 previously unknown A-type peculiar stars. They also found 34 weak G-band giants stars in the southern hemisphere. Their study was called a "major contribution" in providing data to help identify the relatively rare Population II stars. It created an unbiased sample, and doubled the number of known peculiar A-type (Ap) stars. After nineteen years of study by various investigators, in 2014, Beers et al. studied 302 of the Bidelman-MacConnell possible weak-metal stars and concluded that a metal-weak thick disk (MWTD) is present in the Milky Way galaxy, and noted its importance in understanding the development of our galaxy.
In 1962 and 1966, Bidelman had reported that the wavelength of λ 3984 varied somewhat from star to star, and stated differences in the ratios of mercury isotopes could be the reason. Bidelman was the first to note this, and in 1974, Michaud, Reeves and Charland, considering the isotopic abundances to be real, and that Hg was in fact overabundant and not an artifact of blending, suggested the mercury overabundances were due to radiation pressure that caused the element to pile up until radiation and gravitational forces almost cancelled each other, then its isotopes would separate, sorting themselves. Michaud suggested that element segregation would proceed naturally due to gravitational settling and radiation pressure if the stellar atmosphere was steady.
In 1975, Bidelman and San-Gak Lee reported spectral classifications for 601 proper-motion stars that had been listed in both a Lowell Observatory survey under Henry L. Giclas, and the Luyten Two-Tenths Catalogue and supplement, and their report included data from Gerard Kuiper. Kuiper and Bidelman had been at Yerkes Observatory at the same time.
 For six years Kuiper had worked to classify ~3,200 high proper motion stars using ~9,000 spectra taken at Yerkes and McDonald, and with an added 300 spectra from Luyten, Kuiper had planned to publish the data with Luyten. Bidelman called it "very important spectroscopic work and a "large-scale assault" on the problem of unclassified proper motion stars.
When Kuiper ran out of stars of large proper motion and parallax in a region of sky, he observed the planets and their moons "nicely lined up" in that region. When Kuiper found evidence of an atmosphere on Saturn's moon, Titan, his research changed focus and much of his data on proper motion stars remained unpublished. Kuiper died in 1973.
Following his paper with Lee, Bidelman had "renewed interest" in proper motion stars and asked whether Kuipers unpublished proper motion material could be found. With help from the Kuiper Memorial Committee at the University of Arizona, Ewen A. Whitaker, Elizabeth Roemer, and Helmut Abt, Bidelman obtained copies of five of Kuipers notebooks which had stars noted by name and right ascension without declination, and many with multiple spectra and more than one classification. Bidelman established a card file for every star or binary pair, and sought to find the exact star Kuiper observed. His goal was not to create definitive spectral types or change Kuipers classifications, but to set out clearly "the enormous amount of useful spectral data relating to these objects gathered by an energetic and most talented astronomer to whom many, including the writer, owe much. This work represents a partial repayment of that debt". He estimated there could be ~1,000 stars with better spectral types than otherwise known. Bidelman worked on Kuipers data. and published it in 1985.
In 1975, Peter Pesch replaced Bidelman as Director of the Observatory and Chairman of the Astronomy department. While Bidelman had been the observatory director, three of Bidelman's graduate students, Craig Chester, Cynthia Irvine, and William Smethells, were part of a group from CWRU who wanted to begin their own observatory. The outlook for employment in research astronomy was bleak, so the group began a mail-order business and took part-time jobs to solve their "food on the table problem" while seeking to build an observatory in California, and Bidelman gave them their first cash donation. Other donations followed, and the Monterey Institute for Research in Astronomy opened in 1984.
In 1976, Bidelman headed an IAU working group on the proper designation for astronomical objects. At a 1978 symposium discussion following a paper Bidelman stated he wanted to make a slightly off-topic point about nomenclature, and asked whether the star under discussion, VI Cyg #5 is the same star as BD+40° 4220. Informed it is and another one of its names is V729 Cyg, Bidelman responded, "Well, Id like to say, as a member of an IAU Commission concerned with such things, that one should adopt a consistent labeling for a star". After being seconded by Underhill, he added: "We dont all have encyclopedic memories".
The Warner and Swasey Observatory in Cleveland, Ohio, suffered from light pollution, and was moved first to a better viewing site in Ohio, then later to Kitt Peak, Arizona, in 1979. By 1979, Houk had classified 69,000 southern stars. As she finished the southern classifications, Bidelman became responsible to oversee taking the northern plates at CWRU's new Kitt Peak observation site in Arizona. The Curtis Schmidt telescope that was used for the southern all-sky survey was a twin to the Burrell Schmidt used in the northern survey.
When the telescope at Kitt Peak became operational in 1981, Bidelman continued his "early-results" research involving "systematic, but nonetheless somewhat cursory inspection" to classify stars for the northern hemisphere that had been given HD numbers, and published the spectral data in 1983. Bidelman identified 175 peculiar or otherwise interesting stars, most thought to be new discoveries.
Bidelman was the first to identify the peculiar F str λ4077 dwarfs. As part of the "early results" program, in 1981, 1983 and 1985 Bidelman found 21 stars he identified as "F str λ 4077". Almost nothing was known about these stars other than Bidelman's spectral classification. Later researchers found evidence that about half are main-sequence counterparts of Barium stars.
Bidelman retired from teaching at Case Western in 1986. He became a Professor Emeritus, and in 1990 and 1991 continued to do research and remained active in the astronomy department. As a Professor Emeritus, Bidelman continued with the Henry Draper Reclassification project with Houk and the Michigan Spectral Survey and compiled identification of stars in the IRAS Low-Resolution Spectral Catalogue.
Bidelman became interested in the Star of Bethlehem and argued it was involved planetary conjunctions. In 1991, Bidelman used astronomical tables by Bryant Tuckerman and Jean Meeus to investigate Roger Sinnotts suggestion that two close conjunctions of Venus and Jupiter on the morning of August 12, 3 BC, and the evening of June 17, 2 BC, could explain the Star of Bethlehem. He found that for these two planets, an easily observable morning conjunction is "invariably followed" by an evening conjunction approximately ten months later whenever the morning conjunction has an elongation of at least 19°. Bidelman found 28 such pairs of Venus-Jupiter conjunctions in the ~100 years before the birth of Christ, although the 3 and 2 BC conjunctions appeared closer together. Bidelman noted that John Mosley has shown the August 3 BC morning conjunction was ~4.3 arcminutes, and the June 2 BC evening conjunction was an "extremely close" 0.5 arcminutes, and Bidelman considered some historical events to determine the date of Christs birth, and noted these conjunctions took place in Leo, a constellation associated with Judaism and the Tribe of Judah. Bidelman suggested the conjunctions in 3 and 2 BC are a plausible explanation for the Star of Bethlehem.
In a brief 1991 Newsweek on Air interview about the Star of Bethlehem, when asked when and why he became interested in the topic, Bidelman said he had always been an astronomer, and it is of astronomical interest. When asked whether he thought his theory demystified Christmas, Bidelman replied:
In 1992, almost 50 years after his thesis paper, Bidelman stated On revient toujours à ses premières amours ("One always returns to his first loves") when he returned to the topic of his dissertation in 1992 and he considered it "perhaps worth mentioning" that two stars seen then had completely changed their spectral appearance.
In 1993, Bidelman provided data on 177 known and possible asymptotic giant branch stars, saying he was confident many would "prove to be interesting and important. Unfortunately, I dont know which ones!" Bidelmans list of high Strömgren c1 index high galactic latitude stars included promising post-AGB candidates to lead to finds of similar objects to better understand the post-AGB sub-groups of stars.
Invited to speak at the 1996 IAU Symposium on carbon stars Bidelman declined on advice from his doctor, but sent introductory comments in which he said:
Pointing out that observers sometimes "note things that don't seem to make much sense, but which later are realized to have been very significant indeed", he traced a brief history of "this stellar oddball" and concluded:
In May 1998, the Case astronomy students and graduates held a 2-day "Kth" reunion to honor Bidelman and new retiree Peter Pesch.
Bidelman (1969) once said that the problem of the Ap stars (1969) is that "stars of unusual spectrum are doing unusual things". In 2002, Bidelman suggested the peculiar magnetic A stars may have once been close binaries that "merged and are now in the process of learning to live as single objects", and suggested in 2005 that Przybylski's Star may be one such object.
In Case Western University's 2008 astronomy department newsletter, Chair Heather Morrison wrote they were sorry to say goodbye to Professor Bidelman, who had turned 90 "and has decided to finish his distinguished career in Astronomy by retiring for a second time".