The celestial sphere can be described as a

The celestial sphere is a fictional sphere to which all celestial objects can be projected.

Explanation:

At any time an observer can see only the half of celestial sphere because the other half lies under the horizon. The celestial sphere is the medium used for sphere astronomy. The celestial sphere does not have a defined magnitude. It can be infinite or at least really big.

tunami b/c it is near water