sky
穹 centers on the sky as a vast, overarching dome or vault. It conveys the sense of the heavens as a high, curved expanse.
穹 combines 穴 (hole, cavity) with 弓 (bow), likely suggesting the arched shape of the sky as a bow-like vault. The exact historical development is uncertain, but the components visually reinforce the idea of a curved expanse.
The top 穴 looks like a cave opening, and the bottom 弓 is a bow. Imagine looking up from a deep cave and seeing the sky arched like a giant bow overhead.
For キュウ, picture a cue ball (as in billiards) arcing through the sky like a bow: cue -> キュウ, and the ball traces the vault of heaven.