Celestial Sphere


Celestial Sphere is an imaginary sphere of infinite radius with the earth at its center and poles aligned with the earth’s poles and equator with earth’s equator. This sphere is used in spherical astronomy to describe the positions and motions of stars and other objects.

It was a common belief in ancient times that stars were attached to the celestial sphere and they revolved around the planet in only one day. It was also believed that earth is fixed. The celestial sphere allows us to maintain references to different celestial bodies located in the sky.


Quick Facts: –

  • This sphere can be thought as the underside of a dome.
  • The Eudoxan Planetary Model was the first one to explain how classical planets wandered.
  • The Celestial Surface is too large in proportion to the Earth’s size.
  • This sphere is divided halfway by the celestial equator and circles of declination are parallel to it.
  • We only see half of a sphere and we know that the other half exists down below us.
  • The stars appear to move together across the sky during the night. They rise in the east and set in the west as if they are affixed to the inside of the dome.
  • The earth bulges slightly at its equator because of the continuous rotation.
  • The point directly overhead on the celestial sphere is the zenith of the sphere.
  • The oldest remaining celestial globe dates back to the 2nd century sculpture. It is known as the Farnese Atlas.
  • Diurnal motion is the reason why stars rise in the east and set in the west and move through the north-south line.