On the Nature and Construction of the Sun and Fixed Stars

On the Nature and Construction of the Sun and Fixed Stars, by William Herschel, published in the Philosophical Transactions of the Royal Society in 1795, is the astronomer's own primary paper proposing that the Sun has a cool, possibly inhabited solid interior beneath its luminous outer layer, an idea Herschel extended to stars generally. Its strength is that it is Herschel's own observational reasoning in his own words, valuable here as a primary record of how a leading astronomer of his era, working from real telescopic observation of sunspots, reasoned about solar structure before spectroscopy or nuclear physics existed to correct him. Its limit is severe by modern standards, the actual claim, that the Sun harbors a habitable solid core, is false and was already a minority and soon abandoned position even in its own period, so it should be cited only as a historical document illustrating period astronomical reasoning and the once serious idea of solar habitability, never as an accurate description of the Sun.