Having laid out the star catalog, Ptolemy next faces a somewhat more abstract challenge: attempting to describe the nebulous structure of the Milky Way. He first describes the general shape and color:
Now the Milky Way is not strictly speaking a circle, but rather a belt of a sort of milky colour overall (whence it got its name); moreover this belt is neither uniform nor regular, but varies in width, colour, density and situation, and in one section is bifurcated. [All] that is very apparent even to the casual eye, but the details, which can only be determined by a more careful examination, we find to be as follows.
There’s not really much to discuss here, so instead, I’ll combine Ptolemy’s descriptions with some screenshots from Stellarium to help highlight what he’s talking about.
Continue reading “Almagest Book VIII: On the Location of the Milky Way”