L asked:

I've only seen "Pythagoras" as the originator of the Hesperus/ Phosphorus distinction. Someone on a
mailing list said it was attributed to Parmenides. Is there anything to back this up?

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As Pythagoras wrote nothing, it is hard to say how much of the doctrine we know as Pythagorean" is
due to the founder of the society and how much is later development. According to the book Die
Fragmente der Vorsokratiker" by Hermann Alexander Diels, which can be said to be one of the most
reliable presentations of presocratic philosophy, Pythagoras (or at least one of his disciples) was the
first Greek to recognize that the morning star (Phosphorus) and the evening star (Hesperus) were in
fact one star. After his time it was called Aphrodite, and nowadays we know it as the planet Venus.
He was also the first to note that the orbit of the moon is not in the plane of the earth's equator but is
inclined at an angle to that plane. Though there is reason to believe that Parmenides was highly
influenced by the Pythagorean cosmology, I couldn't find any indication, that Parmenides discovered
the identity of Hesperus and Phosphorus.

Simone Klein