the firmament
Definitions
The vault or arch of the sky; the heavens.
The sphere or world in which something exists or operates.
Examples
The stars twinkled brightly across the vast expanse of the firmament.
As the sun began to set, the colors of the twilight painted the firmament in shades of orange and purple.
Synonyms
the heavens the sky the celestial sphere the vault of heaven the blue yonder
Antonyms
the underworld the abyss the earth the ground the nether regions