The words ᾰ̓́στρον (ástron) and ᾰ̓στήρ (astḗr) both apparently refer to a celestial body (typically stars and planets).
Other than ᾰ̓́στρον being a 'second declension' noun and ᾰ̓στήρ being a 'third declension' noun, and ᾰ̓στήρ having additional meanings (an illustrious person, a starfish, a songbird) I can't find any significant difference between the two.
According to Wiktionary ᾰ̓́στρον is derived from ᾰ̓στήρ, but there's nothing to indicate any usage difference between the two when used in the sense of 'star' or 'planet'.
Hence I would like to know:
- Is there any particular usage difference between the two, or are they interchangable (for the 'star'/'planet' sense)?
- If there is a difference in meaning or usage (for the 'star'/'planet' sense), what is that difference?
- Is there some reason why ᾰ̓́στρον came into existance?
- Does it fill a role or provide a meaning that ᾰ̓στήρ does not?
- Does it disambiguate between other meanings of ᾰ̓στήρ?
- Is it simply an attempt to Hellenise a word of proto-Indo-European origin, or to make it more suited to a particular dialect of Ancient Greek (e.g. Attic, Ionic, Aeolic, Doric)?
(Please note that I know little about Latin or Greek grammar, so if there is some grammatical difference, e.g. if the 'second' and 'third' declension difference has some significance that I am unaware of, it would be helpful if that were explained, or if a reference to an explanation were provided.)