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This answer to Has great eyesight been necessary for astronomers? mentions Astronomer Jocelyn Bell Burnell's recounting of a likely first visual observation of a pulsar. This can be found for example in Nature's Air force had early warning of pulsars

The work preceded by several months the observations made by Bell Burnell, then at the University of Cambridge, UK, which led to the first paper on the subject. A Nobel prize for the discovery was subsequently awarded to her supervisor Antony Hewish, but, controversially, not to her. Schisler was not the only one to “pre-discover” a pulsar, though, according to Bell Burnell. “There are actually a lot of stories,” she says. In the 1950s, a woman visiting the observatory at the University of Chicago, Illinois, pointed out that there was a regularly pulsating source of visible light in the Crab Nebula. Elliot Moore, an astronomer at the university, dismissed the woman's claim, telling her that all stars seem to flicker. Another radio astronomer she knows of will, after a drink or two, confess to having dismissed observations of a pulsating source as the result of faulty equipment. “He's a bit embarrassed now,” says Bell Burnell.

This is also summarized in Wikipedia's Crab Pulsar:

Jocelyn Bell Burnell, who co-discovered the first pulsar PSR B1919+21 in 1967, relates that in the late 1950s a woman viewed the Crab Nebula source at the University of Chicago's telescope, then open to the public, and noted that it appeared to be flashing. The astronomer she spoke to, Elliot Moore, disregarded the effect as scintillation, despite the woman's protestation that as a qualified pilot she understood scintillation and this was something else. Bell Burnell notes that the 30 Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see.

Is there any information on who it might have been who noticed the visibly pulsing light at this observatory in Chicago, or which telescope it was and roughly the aperture size?

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Bernell recounts the stories herself in Reflections on the Discovery of Pulsars. She gives a bit more detail, in particular that the telescope was 82 in, but does not name the woman. She also mentions Sue Simkin who noticed pulsations of the Minkowski star in 1965, also before Schisler:

"The first dates from summer 1957 when Elliott Moore helped out at a public observing night at the 82 inch McDonald Observatory telescope (now known as the Otto Struve telescope). For the final observation of the night the telescope was set on the inner part of the Crab Nebula. One member of the public was a young woman probably in her late twenties; she was familiar with the night sky because her job was flying planes a nd in the dark cockpit there was little else to do except watch the stars. After her turn at the telescope she reported that one of the stars in the Crab nebula was blinking rapidly, and described which one. Elliott Moore looked but could not see the effect. He suggested it was scintillation, but later realised that with such a large aperture telescope it couldn’t be.

The second dates from December 1965. Sue Simkin was taking UV spectra with the Carnegie Image Spectrograph at the Kitt Peak 84 inch telescope. She was asked by Lo Woltjer to take a UV spectrum of Minkowski’s star (now known to be the pulsar). She said the spectrum was dull, but as she took it she observed flickering, or as if there were waves going out from it. Lo maintained there couldn’t be, but after the discovery of the pulsar agreed that must have been what she had seen. [The Crab pulsar, with a period of 30Hz, is sufficiently fast that many people cannot see it; however some people can see 30Hz and Sue Simkin knows she is one of them – as a child she lived in an area where the mains power supply was at 30Hz.]"

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    $\begingroup$ This is a triple Wow! answer. 1) two women's keen observations of pulsars were dismissed by two male astronomers (effectively 'you didn't see what you think you saw') (a third was ignored by the Nobel prize committee), 2) I knew professor Simkin (a zillion years ago), 3) there was some place with 30 Hz AC power! $\endgroup$
    – uhoh
    Jan 2, 2020 at 0:35
  • $\begingroup$ fyi I've just asked How low have mains frequencies gone? What areas once used 30 Hz, and why? $\endgroup$
    – uhoh
    Jan 2, 2020 at 0:46
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Sue Simkin was my sister (she recently passed away). I have a suggestion for another explanation (rather than Detroit electricity), based on family experiences, that might have been how she could recognize 30 Hz pulsing. When we were children, our family visited a great aunt every summer. The aunt lived in Scotland, Ontario (near Brantford). The lighting there was pulsing. It might have been that what Sue remembered was the pulsing of the light in our aunt's house. I'll try asking our brother (who is an electrical engineer) if he remembers details about the lighting there.

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    $\begingroup$ Thank you for your answer and for sharing your story, and I'm very sorry for your loss. I took a few of her classes in the late 1970's including an observational astronomy laboratory at the observatory south of campus, then TAed it for her, and it was a real pleasure to learn from her and also to "bask in her enthusiasm" for astronomy; fifty years later she still stands out as my favorite astronomy professor! $\endgroup$
    – uhoh
    Feb 24, 2021 at 4:01

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