The celestial sphere can be considered a real sphere at an infinite distance from the Earth. The Earth’s axis, extended to infinity, touches this sphere at the north and south celestial poles, around which the heavens seem to turn. | Encyclopaedia Britannica

Celestial Sphere in Astronomy | Definition & Related Terms

Earth's Celestial Sphere | Stars, Planets, & Heavenly Bodies | Britannica

Celestial Navigation – Local Hour Angle