Caption: Portrait of Auguste Comte (1798--1857).

The positivist philosopher Auguste Comte gave the matter composition of stars as an example of something humankind can NEVER know:

Any research that CANNOT be reduced to actual visual observation is excluded where the stars are concerned ... We can see the possibility of determining their forms, their distances, their magnitudes, and their movements, but it is INCONCEIVABLE that we should ever be able to study, by any means whatsoever, their chemical or mineralogical structure...''
---Auguste Comte (1798--1857), 1835, quotation from Kirk Korista at Professor Korista.

Famous last words.

Just 30 or so years after Comte's statement, the elemental composition of stars was being identified from starlight using spectroscopy (see Wikipedia: Star: Observation history; Wikipedia: Fraunhofer lines: Discovery).

It turns out that stars are mainly hydrogen and helium just as our Sun is.

Of course, spectroscopy is "visual observation" though NOT usually what we mean by visual astronomy (i.e., astronomy by human eye) since almost all useful spectroscopy is recorded by a device. Is Comte right that all we can understand about stars depends on "visual observation"? Yes and no. Theory, modeling, and terrestrial observations can tell us a lot, but without visual observation including spectroscopy, our understanding would be very limited and uncertain.

Credit/Permission: Louis-Jules Etex (1810-1889), 19th century (uploaded to Wikipedia by User:P.S. Burton, 2013) / Public domain.
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