There appear to be no less than five Latin words for "star" (in no particular order):
Now, in English "stella" has become the root word of "stellar", clearly meaning a physical object, namely a big ball of fusing hydrogen and helium, or a point of light which is one of these as viewed from light years away. And in common mottoes, "astra" frequently appears as Latin for "the stars" both as a broad collective group of the same celestial phenomena and a metaphorical appellation for the heavens or simply grand aspirations ("Ad astra per aspera," etc.)
Adstrum I have never seen (might be an Internat error?).
"Sidus" is the source for "sidereal" meaning "of the stars", again the collective objects which are points of light viewed from Earth.
And "lumen" is of course a word for "light," by which I assume (possibly incorrectly) that the meaning "star" in this case is purely contextual and not inherent, just as if I said in English, "all the lights in the night sky" and the hearer understanding that I mean the stars.
However, I do not know the typical context that any of these words might be used in a Latin phrase, and if the choice of a given word carries with it implied meanings or connotations in Latin. Specifically, how might (assuming I have the grammar correct) "Ad stellae per aspera" differ in connation or meaning from "Ad astra per aspera," if at all? Or is the choice "astra" merely one of aesthetic alliteration, with the two words being otherwise completely interchangeable (in good Latin)?
This all bears significance, as I am crafting a series of Latin mottoes for which the actual connotations of the different words will have significance This is part of my current novel WIP, in which a character fluent in Latin recognizes the differences in connotation, and derives hidden meanings in the phrases from this. Alas, I am not that characteró indeed, I had no intention of using such connotations until I began to puzzle over why our own language and mottoes borrowed both the word "stella" as well as the word "astra" from Latin (and yes, I know that "astron" and "astro-" as prefixes come from Greek). It then struck me that perhaps the words in Latin don't mean quite the same thing, and discovering the other potential choices raised the issue even more (as well as making me think, "maybe I could use that…" Which is how every devious little plotter… uh, good fiction writer… responds to such subtleties).
It's been far too many years from my poorly attended to studies in high school Latin for me to know. So I'm throwing it out to the collective TMP crowd for consideration.
Questions to guide you:
What would be the correct word for a star symbol (as a pentagram or a starburst drawn on a surface)?
What would be the correct word for a single, actual star (the big ball of flaming gas)?
What would be the correct word for a group of specific stars (not just "stars" in general), as say the stars in a constellation or on a list of named stars?
Any help will be greatly appreciated!