Note: Marijn van Putten (p.c.) suggests, contrary to the conclusion in Bjørn 2017, that the connection to Semitic is of continued interest. The phonetic matchup is certainly worth entertaining, and I rely heavily on Diakonoff to dismiss the connection on semantic grounds. I hope to return to this etymology again and invite the reader to share arguments for and against in the comment section below.
Gloss: ‘star’ (item 55 in Bjørn 2017)
Attestations: Hit. ḫaster-; Toch. A śreñ (pl.), Toch. B ścirye; Lat. stēlla; OIr. ser; Goth. staírno; Gr. ἀστῆρ; Arm. astl; Ved. stár-, Av. star-.
Notes: Latin requires an *-l- derivation that seems to be resonated in Celtic (de Vaan 2008: 585). The term is widespread and retains its meaning in all branches of attestation, making a reconstruction for the earliest strata of PIE unavoidable. Bomhard suggests that the noun is internally derived from the verb *h2eh1-s– ‘to burn, dry’ (1986).
Semitic: *ʕaθar(-at)– ‘Venus, deified star’
Apparently a religious symbol in the Proto-Semitic world, the formation is not included by Orel & Stolbova (1995), which necessarily has consequences for the evaluation of possible provenance. Since the word is attested in IE to warrant reconstruction of an old and concrete meaning ‘star’, it is significantly more attractive to posit PIE as the potential provider vis-a-vis from the specialized and culturally dependent meaning in Semitic as propounded by Dolgopolsky (1987: 15f., 1993: 244). Moreover, the connotations in Semitic conducive for the comparison are demonstrably secondary cultural attributes to the deity (Diakonov 1985: 122f.), so this comparison can safely be ascribed to chance.