” While he gazed upward, into the deep arch of the firmament, and..” (47)
Firmament is the curve of the sky thought of as a solid object.
Firmament
fir·ma·ment
noun
1) The heavens or the sky, especially when regarded as a tangible thing.
2) A sphere or world viewed as a collection of people.
“one of the great stars in the American golfing firmament”
