Assertion: celestial sphere | /r/HasProperty | practical tool
Facets:
value: for spherical astronomy
type: PURPOSE
Source sentences:
text: The celestial sphere is a practical tool for spherical astronomy, allowing astronomers to specify the apparent positions of objects in the sky if their distances are unknown or irrelevant.
text: The celestial sphere is a practical tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant.