Neil - I had no idea this could mean cloud! :) I have several family members named
Neil.
Gemini - I like it, but prefer it for a girl.
Callisto - Never thought about masculine usage, but love it.
Celestia - Personally, I prefer
Celeste or
Celestina.
Europa - She was raped by a bull in Greek mythology...that kills any appeal it might otherwise hold to me.
Names I like, but not enough that I would use them:
Luna,
Laine,
Lyra,
Phoebe,
Nova,
Arista,
Estella,
Cynthia,
Leo,
Aries,
Orion (plus
Sirius,
Andromeda,
Bellatrix because they're heavily associated with
Harry Potter).
More astronomy/weather names:
Maia,
Miranda,
Altair, Antares, Aldebaran,
Oberon,
Ariel,
Cassiopeia,
Vega,
Aludra, Capella,
Atlas,
Electra,
Mira, Polaris,
Rigel,
Phoenix, Lycoris,
Alcyone,
Soleil, Mercutio,
Aquila, Acamar, Eridanus, Metis,
Amalthea,
Vesta,
Dione,
Charon,
Eris,
Barak, Darjeeling,
Jaswinder,
Thora,
Soraya, Ashni, Levina,
Aeolus,
Anemone,
Zephyra...