…
relating to sky as in celestial bodies, celestial spectacle
Of the heavens, at the top
All the meanings that it has for me extend from the one meaning: Heavenly.
The two most likely derivative meanings, in no particular order will be:
Relating to stars.
Relating to angels. Or, it could be used as a noun to mean ‘an angel, or similar heavenly being’.
Also:
Something extremely good - like it’s from heaven.
Relating to God or gods (as God traditionally resides in the heavens, and that got extended to other gods, who don’t necessarily do so).
The closest synonym I can think of is “heavenly.” My understanding is that it just has something to do with the sky, and is typically used in a religious context, but does not technically or exclusively have that connection.
“heavenly.”
Having read other answers “Things related to the sky or stars” wouldn’t be my first thought. But it might have shown up eventually if I had given more than two minutes of thought to it.
In or of the stars or heavenly bodies. I have seen this on a Chinese menu before though, and it was used completely incorrectly. I think they even used “a galaxy of shrimp” and I’m not joking.
Uh… I just finished reading everybody else’s answers so far, thinking for sure someone would have already mentioned this… but…
“Celestial Empire”, referring to China in the days of empire. And thus, “celestial” referring to a Chinese person, especially in (or perhaps up to and including) the 19th century (and maybe early 20th century)?
[spoiler]Pertaining to the heavens, in an astronomical sense.
Pertaining to heaven, in a religious sense.
The epitome of goodness.
[/spoiler]
[spoiler]Have heard that meaning, yes - but only, as you say, in 19th century literature. And even then I don’t get the impression that is was super common. Didn’t they use “Chinaman” or even “Chinee” more?
I’ve just looked it up. Wikipedia claims the term was “widely used in the popular mass media,” but one of their cites (their link was dead, so I found the article myself) uses “Chinese” and “Chinaman” far more often than “Celestial.”
Anyway, is that the meaning the OP was going for??
[/spoiler]
Mine are all in the same vein:
Pertaining to the heavens. Heavenly.
Pertaining to the stars. Stellar.
Pertaining to the constellations. Constellationy. 
Pertaining to what used to be called “the heavens”; i.e., outer space, the realm of the stars, the universe at a scale larger than the planetary scale.
Heavenly.
Star-like.
Unearthly.
OK, I’ll play:
Being of the moon and the stars.
That’s all I can think of.
Heavenly
Please enlighten us (with spoiler tags)! I just spent ten minutes trying to find what you’re referring to – I assume it’s pornographic or something – and I found nothing.
My opinion without reading other posts or looking it up:
Multiple uses:
Starry
Pertaining to the sky or heavens (astronomical usage)
Pertaining to Heaven (in a religious sense)
Having to do with the heavens or the sky
So, what’s the reason?
Of the stars. It’s a reference to things in the night sky, or “the heavens” if you’re feeling poetic