My point about the writing (and the later rewriting) of scientific history, and about the correct - or incorrect - assignment of the credit for a discovery to a particular person, is relevant when we try to assess the truth or partial-truth of the biography of W.W.Morgan by William Sheehan. When it comes to discussing who discovered and first mapped the spiral arms near the Sun, Sheehan's view is that the credit is all to "Morgan!...Morgan!...Morgan!"
Given the powerful and colourful prose of Sheehan, and the fact that science writers like to plant in the reader's mind the
very powerful myth of the "lone genius who sees so much further than others", most readers of this biography of Morgan will probably conclude: "It must have been thus!"
But I hasten to point out that while W.W. Morgan was undoubtedly one of the very most important astronomers of his generation, the short note in the Astronomical Journal that announced the discovery of our Galaxy's local Spiral Structure is by W.W. Morgan
and Stewart Sharpless
and Donald Osterbrock:
http://adsabs.harvard.edu/abs/1952AJ.....57....3M
Given that the scientific contributions of Stewart Sharpless have largely been forgotten, with the exception of his Very Important catalog of bright nebulae, I think it would be important to accurately assess whether or not he had only a small part in the discovery;
really, it is not fair of Sheehan to
assign credit to only one of the three authors of the paper.
I think it is significant that Bart Bok, who was also
active in the early 1950s in the elucidation of the structure of our own Galaxy, refers (in the fifth edition of "The Milky Way") to the fundamental diagram of the nearby spiral arms as
The Morgan-Osterbrock-Sharpless diagram
[[ Don't forget that in those days, senior astronomers found it easy to hog the credit that belonged in part to their junior co-researchers.
Hubble himself was one of the greatest offenders in this regard, especially in his very shabby treatment of Humason! (and also of Georges Lemaitre) ]]